freeipa/ipalib/parameters.py
Nathaniel McCallum 4499b25be9 Remove NULLS from constants.py
In the parameters system, we have been checking for a positive list of values
which get converted to None. The problem is that this method can in some
cases throw warnings when type coercion doesn't work (particularly, string
to unicode). Instead, any values that evaluate to False that are neither
numeric nor boolean should be converted to None.

Reviewed-By: Jan Pazdziora <jpazdziora@redhat.com>
2014-02-25 16:05:19 +01:00

1865 lines
63 KiB
Python

# Authors:
# Jason Gerard DeRose <jderose@redhat.com>
#
# Copyright (C) 2008 Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
Parameter system for command plugins.
A `Param` instance can be used to describe an argument or option that a command
takes, or an attribute that a command returns. The `Param` base class is not
used directly, but there are many subclasses for specific Python data types
(like `Str` or `Int`) and specific properties (like `Password`).
To create a `Param` instance, you must always provide the parameter *name*,
which should be the LDAP attribute name if the parameter describes the attribute
of an LDAP entry. For example, we could create an `Str` instance describing the user's last-name attribute like this:
>>> from ipalib import Str
>>> sn = Str('sn')
>>> sn.name
'sn'
When creating a `Param`, there are also a number of optional kwargs which
which can provide additional meta-data and functionality. For example, every
parameter has a *cli_name*, the name used on the command-line-interface. By
default the *cli_name* is the same as the *name*:
>>> sn.cli_name
'sn'
But often the LDAP attribute name isn't user friendly for the command-line, so
you can override this with the *cli_name* kwarg:
>>> sn = Str('sn', cli_name='last')
>>> sn.name
'sn'
>>> sn.cli_name
'last'
Note that the RPC interfaces (and the internal processing pipeline) always use
the parameter *name*, regardless of what the *cli_name* might be.
A `Param` also has two translatable kwargs: *label* and *doc*. These must both
be `Gettext` instances. They both default to a place-holder `FixMe` instance,
a subclass of `Gettext` used to mark a missing translatable string:
>>> sn.label
FixMe('sn')
>>> sn.doc
FixMe('sn')
The *label* is a short phrase describing the parameter. It's used on the CLI
when interactively prompting for values, and as a label for form inputs in the
web-UI. The *label* should start with an initial capital. For example:
>>> from ipalib import _
>>> sn = Str('sn',
... cli_name='last',
... label=_('Last name'),
... )
>>> sn.label
Gettext('Last name', domain='ipa', localedir=None)
The *doc* is a longer description of the parameter. It's used on the CLI when
displaying the help information for a command, and as extra instruction for a
form input on the web-UI. By default the *doc* is the same as the *label*:
>>> sn.doc
Gettext('Last name', domain='ipa', localedir=None)
But you can override this with the *doc* kwarg. Like the *label*, the *doc*
should also start with an initial capital and should not end with any
punctuation. For example:
>>> sn = Str('sn',
... cli_name='last',
... label=_('Last name'),
... doc=_("The user's last name"),
... )
>>> sn.doc
Gettext("The user's last name", domain='ipa', localedir=None)
Demonstration aside, you should always provide at least the *label* so the
various UIs are translatable. Only provide the *doc* if the parameter needs
a more detailed description for clarity.
"""
import re
import decimal
import base64
from xmlrpclib import MAXINT, MININT
from types import NoneType
from text import _ as ugettext
from plugable import ReadOnly, lock, check_name
from errors import ConversionError, RequirementError, ValidationError
from errors import PasswordMismatch, Base64DecodeError
from constants import TYPE_ERROR, CALLABLE_ERROR
from text import Gettext, FixMe
from util import json_serialize
from ipapython.dn import DN
def _is_null(value):
return not value and value != 0 # NOTE: False == 0
class DefaultFrom(ReadOnly):
"""
Derive a default value from other supplied values.
For example, say you wanted to create a default for the user's login from
the user's first and last names. It could be implemented like this:
>>> login = DefaultFrom(lambda first, last: first[0] + last)
>>> login(first='John', last='Doe')
'JDoe'
If you do not explicitly provide keys when you create a `DefaultFrom`
instance, the keys are implicitly derived from your callback by
inspecting ``callback.func_code.co_varnames``. The keys are available
through the ``DefaultFrom.keys`` instance attribute, like this:
>>> login.keys
('first', 'last')
The callback is available through the ``DefaultFrom.callback`` instance
attribute, like this:
>>> login.callback # doctest:+ELLIPSIS
<function <lambda> at 0x...>
>>> login.callback.func_code.co_varnames # The keys
('first', 'last')
The keys can be explicitly provided as optional positional arguments after
the callback. For example, this is equivalent to the ``login`` instance
above:
>>> login2 = DefaultFrom(lambda a, b: a[0] + b, 'first', 'last')
>>> login2.keys
('first', 'last')
>>> login2.callback.func_code.co_varnames # Not the keys
('a', 'b')
>>> login2(first='John', last='Doe')
'JDoe'
If any keys are missing when calling your `DefaultFrom` instance, your
callback is not called and ``None`` is returned. For example:
>>> login(first='John', lastname='Doe') is None
True
>>> login() is None
True
Any additional keys are simply ignored, like this:
>>> login(last='Doe', first='John', middle='Whatever')
'JDoe'
As above, because `DefaultFrom.__call__` takes only pure keyword
arguments, they can be supplied in any order.
Of course, the callback need not be a ``lambda`` expression. This third
example is equivalent to both the ``login`` and ``login2`` instances
above:
>>> def get_login(first, last):
... return first[0] + last
...
>>> login3 = DefaultFrom(get_login)
>>> login3.keys
('first', 'last')
>>> login3.callback.func_code.co_varnames
('first', 'last')
>>> login3(first='John', last='Doe')
'JDoe'
"""
def __init__(self, callback, *keys):
"""
:param callback: The callable to call when all keys are present.
:param keys: Optional keys used for source values.
"""
if not callable(callback):
raise TypeError(
CALLABLE_ERROR % ('callback', callback, type(callback))
)
self.callback = callback
if len(keys) == 0:
fc = callback.func_code
if fc.co_flags & 0x0c:
raise ValueError("callback: variable-length argument list not allowed")
self.keys = fc.co_varnames[:fc.co_argcount]
else:
self.keys = keys
for key in self.keys:
if type(key) is not str:
raise TypeError(
TYPE_ERROR % ('keys', str, key, type(key))
)
lock(self)
def __repr__(self):
args = (self.callback.__name__,) + tuple(repr(k) for k in self.keys)
return '%s(%s)' % (
self.__class__.__name__,
', '.join(args)
)
def __call__(self, **kw):
"""
Call the callback if all keys are present.
If all keys are present, the callback is called and its return value is
returned. If any keys are missing, ``None`` is returned.
:param kw: The keyword arguments.
"""
vals = tuple(kw.get(k, None) for k in self.keys)
if None in vals:
return
try:
return self.callback(*vals)
except StandardError:
pass
def parse_param_spec(spec):
"""
Parse shorthand ``spec`` into to ``(name, kw)``.
The ``spec`` string determines the parameter name, whether the parameter is
required, and whether the parameter is multivalue according the following
syntax:
====== ===== ======== ==========
Spec Name Required Multivalue
====== ===== ======== ==========
'var' 'var' True False
'var?' 'var' False False
'var*' 'var' False True
'var+' 'var' True True
====== ===== ======== ==========
For example,
>>> parse_param_spec('login')
('login', {'required': True, 'multivalue': False})
>>> parse_param_spec('gecos?')
('gecos', {'required': False, 'multivalue': False})
>>> parse_param_spec('telephone_numbers*')
('telephone_numbers', {'required': False, 'multivalue': True})
>>> parse_param_spec('group+')
('group', {'required': True, 'multivalue': True})
:param spec: A spec string.
"""
if type(spec) is not str:
raise TypeError(
TYPE_ERROR % ('spec', str, spec, type(spec))
)
_map = {
'?': dict(required=False, multivalue=False),
'*': dict(required=False, multivalue=True),
'+': dict(required=True, multivalue=True),
}
end = spec[-1]
if end in _map:
return (spec[:-1], _map[end])
return (spec, dict(required=True, multivalue=False))
__messages = set()
def _(message):
__messages.add(message)
return message
class Param(ReadOnly):
"""
Base class for all parameters.
Param attributes:
=================
The behavior of Param class and subclasses can be controlled using the
following set of attributes:
- cli_name: option name in CLI
- cli_short_name: one character version of cli_name
- label: very short description of the parameter. This value is used in
when the Command output is printed to CLI or in a Command help
- doc: parameter long description used in help
- required: the parameter is marked as required for given Command
- multivalue: indicates if the attribute is multivalued
- primary_key: Command's parameter primary key is used for unique
identification of an LDAP object and for sorting
- normalizer: a custom function for Param value normalization
- default_from: a custom function for generating default values of
parameter instance
- autofill: by default, only `required` parameters get a default value
from the default_from function. When autofill is enabled, optional
attributes get the default value filled too
- query: this attribute is controlled by framework. When the `query`
is enabled, framework assumes that the value is only queried and not
inserted in the LDAP. Validation is then relaxed - custom
parameter validators are skipped and only basic class validators are
executed to check the parameter value
- attribute: this attribute is controlled by framework and enabled for
all LDAP objects parameters (unless parameter has "virtual_attribute"
flag). All parameters with enabled `attribute` are being encoded and
placed to an entry passed to LDAP Create/Update calls
- include: a list of contexts where this parameter should be included.
`Param.use_in_context()` provides further information.
- exclude: a list of contexts where this parameter should be excluded.
`Param.use_in_context()` provides further information.
- flags: there are several flags that can be used to further tune the
parameter behavior:
* no_display (Output parameters only): do not display the parameter
* no_create: do not include the parameter for crud.Create based
commands
* no_update: do not include the parameter for crud.Update based
commands
* no_search: do not include the parameter for crud.Search based
commands
* no_option: this attribute is not displayed in the CLI, usually
because there's a better way of setting it (for example, a
separate command)
* virtual_attribute: the parameter is not stored physically in the
LDAP and thus attribute `attribute` is not enabled
* suppress_empty (Output parameters only): do not display parameter
value when empty
* ask_create: CLI asks for parameter value even when the parameter
is not `required`. Applied for all crud.Create based commands
* ask_update: CLI asks for parameter value even when the parameter
is not `required`. Applied for all crud.Update based commands
* req_update: The parameter is `required` in all crud.Update based
commands
* nonempty: This is an internal flag; a required attribute should
be used instead of it.
The value of this parameter must not be empty, but it may
not be given at all. All crud.Update commands automatically
convert required parameters to `nonempty` ones, so the value
can be unspecified (unchanged) but cannot be deleted.
* optional_create: do not require the parameter for crud.Create
based commands
* allow_mod_for_managed_permission: permission-mod allows changing
the parameter for managed permissions
- hint: this attribute is currently not used
- alwaysask: when enabled, CLI asks for parameter value even when the
parameter is not `required`
- sortorder: used to sort a list of parameters for Command. See
`Command.finalize()` for further information
- csv: this multivalue attribute used to be given in CSV format in CLI
"""
# This is a dummy type so that most of the functionality of Param can be
# unit tested directly without always creating a subclass; however, a real
# (direct) subclass must *always* override this class attribute.
# If multiple types are permitted, set `type` to the canonical type and
# `allowed_types` to a tuple of all allowed types.
type = NoneType # Ouch, this wont be very useful in the real world!
# Subclasses should override this with something more specific:
type_error = _('incorrect type')
# _convert_scalar operates only on scalar values
scalar_error = _('Only one value is allowed')
password = False
kwargs = (
('cli_name', str, None),
('cli_short_name', str, None),
('label', (basestring, Gettext), None),
('doc', (basestring, Gettext), None),
('required', bool, True),
('multivalue', bool, False),
('primary_key', bool, False),
('normalizer', callable, None),
('default_from', DefaultFrom, None),
('autofill', bool, False),
('query', bool, False),
('attribute', bool, False),
('include', frozenset, None),
('exclude', frozenset, None),
('flags', frozenset, frozenset()),
('hint', (str, Gettext), None),
('alwaysask', bool, False),
('sortorder', int, 2), # see finalize()
('csv', bool, False),
('option_group', unicode, None),
# The 'default' kwarg gets appended in Param.__init__():
# ('default', self.type, None),
)
@property
def allowed_types(self):
"""The allowed datatypes for this Param"""
return (self.type,)
def __init__(self, name, *rules, **kw):
# We keep these values to use in __repr__():
self.param_spec = name
self.__kw = dict(kw)
# Merge in kw from parse_param_spec():
(name, kw_from_spec) = parse_param_spec(name)
if not 'required' in kw:
kw['required'] = kw_from_spec['required']
if not 'multivalue' in kw:
kw['multivalue'] = kw_from_spec['multivalue']
self.name = check_name(name)
self.nice = '%s(%r)' % (self.__class__.__name__, self.param_spec)
# Add 'default' to self.kwargs and makes sure no unknown kw were given:
assert all(type(t) is type for t in self.allowed_types)
if kw.get('multivalue', True):
self.kwargs += (('default', tuple, None),)
else:
self.kwargs += (('default', self.type, None),)
if not set(t[0] for t in self.kwargs).issuperset(self.__kw):
extra = set(kw) - set(t[0] for t in self.kwargs)
raise TypeError(
'%s: takes no such kwargs: %s' % (self.nice,
', '.join(repr(k) for k in sorted(extra))
)
)
# Merge in default for 'cli_name', label, doc if not given:
if kw.get('cli_name') is None:
kw['cli_name'] = self.name
if kw.get('label') is None:
kw['label'] = FixMe(self.name)
if kw.get('doc') is None:
kw['doc'] = kw['label']
# Wrap 'default_from' in a DefaultFrom if not already:
df = kw.get('default_from', None)
if callable(df) and not isinstance(df, DefaultFrom):
kw['default_from'] = DefaultFrom(df)
# We keep this copy with merged values also to use when cloning:
self.__clonekw = kw
# Perform type validation on kw, add in class rules:
class_rules = []
for (key, kind, default) in self.kwargs:
value = kw.get(key, default)
if value is not None:
if kind is frozenset:
if type(value) in (list, tuple, set):
value = frozenset(value)
elif type(value) is str:
value = frozenset([value])
if (
type(kind) is type and not isinstance(value, kind)
or
type(kind) is tuple and not isinstance(value, kind)
):
raise TypeError(
TYPE_ERROR % (key, kind, value, type(value))
)
elif kind is callable and not callable(value):
raise TypeError(
CALLABLE_ERROR % (key, value, type(value))
)
if hasattr(self, key):
raise ValueError('kwarg %r conflicts with attribute on %s' % (
key, self.__class__.__name__)
)
setattr(self, key, value)
rule_name = '_rule_%s' % key
if value is not None and hasattr(self, rule_name):
class_rules.append(getattr(self, rule_name))
check_name(self.cli_name)
# Check that only 'include' or 'exclude' was provided:
if None not in (self.include, self.exclude):
raise ValueError(
'%s: cannot have both %s=%r and %s=%r' % (
self.nice,
'include', self.include,
'exclude', self.exclude,
)
)
# Check that if csv is set, multivalue is set too
if self.csv and not self.multivalue:
raise ValueError('%s: cannot have csv without multivalue' % self.nice)
# Check that all the rules are callable
self.class_rules = tuple(class_rules)
self.rules = rules
if self.query:
# by definition a query enforces no class or parameter rules
self.all_rules = ()
else:
self.all_rules = self.class_rules + self.rules
for rule in self.all_rules:
if not callable(rule):
raise TypeError(
'%s: rules must be callable; got %r' % (self.nice, rule)
)
# Check that cli_short_name is only 1 character long:
if not (self.cli_short_name is None or len(self.cli_short_name) == 1):
raise ValueError(
'%s: cli_short_name can only be a single character: %s' % (
self.nice, self.cli_short_name)
)
# And we're done.
lock(self)
def __repr__(self):
"""
Return an expresion that could construct this `Param` instance.
"""
return '%s(%s)' % (
self.__class__.__name__,
', '.join(self.__repr_iter())
)
def __repr_iter(self):
yield repr(self.param_spec)
for rule in self.rules:
yield rule.__name__
for key in sorted(self.__kw):
value = self.__kw[key]
if callable(value) and hasattr(value, '__name__'):
value = value.__name__
else:
value = repr(value)
yield '%s=%s' % (key, value)
def __call__(self, value, **kw):
"""
One stop shopping.
"""
if _is_null(value):
value = self.get_default(**kw)
else:
value = self.convert(self.normalize(value))
if hasattr(self, 'env'):
self.validate(value, self.env.context, supplied=self.name in kw) #pylint: disable=E1101
else:
self.validate(value, supplied=self.name in kw)
return value
def get_param_name(self):
"""
Return the right name of an attribute depending on usage.
Normally errors should use cli_name, our "friendly" name. When
using the API directly or *attr return the real name.
"""
name = self.cli_name
if not name:
name = self.name
return name
def kw(self):
"""
Iterate through ``(key,value)`` for all kwargs passed to constructor.
"""
for key in sorted(self.__kw):
value = self.__kw[key]
if callable(value) and hasattr(value, '__name__'):
value = value.__name__
yield (key, value)
def use_in_context(self, env):
"""
Return ``True`` if this parameter should be used in ``env.context``.
If a parameter is created with niether the ``include`` nor the
``exclude`` kwarg, this method will always return ``True``. For
example:
>>> from ipalib.config import Env
>>> param = Param('my_param')
>>> param.use_in_context(Env(context='foo'))
True
>>> param.use_in_context(Env(context='bar'))
True
If a parameter is created with an ``include`` kwarg, this method will
only return ``True`` if ``env.context`` is in ``include``. For example:
>>> param = Param('my_param', include=['foo', 'whatever'])
>>> param.include
frozenset(['foo', 'whatever'])
>>> param.use_in_context(Env(context='foo'))
True
>>> param.use_in_context(Env(context='bar'))
False
If a paremeter is created with an ``exclude`` kwarg, this method will
only return ``True`` if ``env.context`` is not in ``exclude``. For
example:
>>> param = Param('my_param', exclude=['foo', 'whatever'])
>>> param.exclude
frozenset(['foo', 'whatever'])
>>> param.use_in_context(Env(context='foo'))
False
>>> param.use_in_context(Env(context='bar'))
True
Note that the ``include`` and ``exclude`` kwargs are mutually exclusive
and that at most one can be suppelied to `Param.__init__()`. For
example:
>>> param = Param('nope', include=['foo'], exclude=['bar'])
Traceback (most recent call last):
...
ValueError: Param('nope'): cannot have both include=frozenset(['foo']) and exclude=frozenset(['bar'])
So that subclasses can add additional logic based on other environment
variables, the entire `config.Env` instance is passed in rather than
just the value of ``env.context``.
"""
if self.include is not None:
return (env.context in self.include)
if self.exclude is not None:
return (env.context not in self.exclude)
return True
def safe_value(self, value):
"""
Return a value safe for logging.
This is used so that sensitive values like passwords don't get logged.
For example:
>>> p = Password('my_password')
>>> p.safe_value(u'This is my password')
u'********'
>>> p.safe_value(None) is None
True
>>> s = Str('my_str')
>>> s.safe_value(u'Some arbitrary value')
u'Some arbitrary value'
"""
if self.password and value is not None:
return u'********'
return value
def clone(self, **overrides):
"""
Return a new `Param` instance similar to this one.
"""
return self.clone_rename(self.name, **overrides)
def clone_rename(self, name, **overrides):
"""
Return a new `Param` instance similar to this one, but named differently
"""
return self.clone_retype(name, self.__class__, **overrides)
def clone_retype(self, name, klass, **overrides):
"""
Return a new `Param` instance similar to this one, but of a different type
"""
kw = dict(self.__clonekw)
kw.update(overrides)
return klass(name, *self.rules, **kw)
def normalize(self, value):
"""
Normalize ``value`` using normalizer callback.
For example:
>>> param = Param('telephone',
... normalizer=lambda value: value.replace('.', '-')
... )
>>> param.normalize(u'800.123.4567')
u'800-123-4567'
If this `Param` instance was created with a normalizer callback and
``value`` is a unicode instance, the normalizer callback is called and
*its* return value is returned.
On the other hand, if this `Param` instance was *not* created with a
normalizer callback, if ``value`` is *not* a unicode instance, or if an
exception is caught when calling the normalizer callback, ``value`` is
returned unchanged.
:param value: A proposed value for this parameter.
"""
if self.multivalue:
if type(value) not in (tuple, list):
value = (value,)
if self.multivalue:
return tuple(
self._normalize_scalar(v) for v in value
)
else:
return self._normalize_scalar(value)
def _normalize_scalar(self, value):
"""
Normalize a scalar value.
This method is called once for each value in a multivalue.
"""
if self.normalizer is None:
return value
try:
return self.normalizer(value)
except StandardError:
return value
def convert(self, value):
"""
Convert ``value`` to the Python type required by this parameter.
For example:
>>> scalar = Str('my_scalar')
>>> scalar.type
<type 'unicode'>
>>> scalar.convert(43.2)
u'43.2'
(Note that `Str` is a subclass of `Param`.)
All non-numeric, non-boolean values which evaluate to False will be
converted to None. For example:
>>> scalar.convert(u'') is None # An empty string
True
>>> scalar.convert([]) is None # An empty list
True
Likewise, they will be filtered out of a multivalue parameter.
For example:
>>> multi = Str('my_multi', multivalue=True)
>>> multi.convert([1.5, '', 17, None, u'Hello'])
(u'1.5', u'17', u'Hello')
>>> multi.convert([None, u'']) is None # Filters to an empty list
True
Lastly, multivalue parameters will always return a ``tuple`` (assuming
they don't return ``None`` as in the last example above). For example:
>>> multi.convert(42) # Called with a scalar value
(u'42',)
>>> multi.convert([0, 1]) # Called with a list value
(u'0', u'1')
Note that how values are converted (and from what types they will be
converted) completely depends upon how a subclass implements its
`Param._convert_scalar()` method. For example, see
`Str._convert_scalar()`.
:param value: A proposed value for this parameter.
"""
if _is_null(value):
return
if self.multivalue:
if type(value) not in (tuple, list):
value = (value,)
values = tuple(
self._convert_scalar(v, i) for (i, v) in filter(
lambda iv: not _is_null(iv[1]), enumerate(value)
)
)
if len(values) == 0:
return
return values
return self._convert_scalar(value)
def _convert_scalar(self, value, index=None):
"""
Convert a single scalar value.
"""
if type(value) in self.allowed_types:
return value
raise ConversionError(name=self.name, index=index,
error=ugettext(self.type_error),
)
def validate(self, value, context=None, supplied=None):
"""
Check validity of ``value``.
:param value: A proposed value for this parameter.
:param context: The context we are running in.
:param supplied: True if this parameter was supplied explicitly.
"""
if value is None:
if self.required or (supplied and 'nonempty' in self.flags):
if context == 'cli':
raise RequirementError(name=self.cli_name)
else:
raise RequirementError(name=self.name)
return
if self.multivalue:
if type(value) is not tuple:
raise TypeError(
TYPE_ERROR % ('value', tuple, value, type(value))
)
if len(value) < 1:
raise ValueError('value: empty tuple must be converted to None')
for (i, v) in enumerate(value):
self._validate_scalar(v, i)
else:
self._validate_scalar(value)
def _validate_scalar(self, value, index=None):
if type(value) not in self.allowed_types:
raise TypeError(
TYPE_ERROR % (self.name, self.type, value, type(value))
)
if index is not None and type(index) is not int:
raise TypeError(
TYPE_ERROR % ('index', int, index, type(index))
)
for rule in self.all_rules:
error = rule(ugettext, value)
if error is not None:
raise ValidationError(
name=self.get_param_name(),
value=value,
index=index,
error=error,
rule=rule,
)
def get_default(self, **kw):
"""
Return the static default or construct and return a dynamic default.
(In these examples, we will use the `Str` and `Bytes` classes, which
both subclass from `Param`.)
The *default* static default is ``None``. For example:
>>> s = Str('my_str')
>>> s.default is None
True
>>> s.get_default() is None
True
However, you can provide your own static default via the ``default``
keyword argument when you create your `Param` instance. For example:
>>> s = Str('my_str', default=u'My Static Default')
>>> s.default
u'My Static Default'
>>> s.get_default()
u'My Static Default'
If you need to generate a dynamic default from other supplied parameter
values, provide a callback via the ``default_from`` keyword argument.
This callback will be automatically wrapped in a `DefaultFrom` instance
if it isn't one already (see the `DefaultFrom` class for all the gory
details). For example:
>>> login = Str('login', default=u'my-static-login-default',
... default_from=lambda first, last: (first[0] + last).lower(),
... )
>>> isinstance(login.default_from, DefaultFrom)
True
>>> login.default_from.keys
('first', 'last')
Then when all the keys needed by the `DefaultFrom` instance are present,
the dynamic default is constructed and returned. For example:
>>> kw = dict(last=u'Doe', first=u'John')
>>> login.get_default(**kw)
u'jdoe'
Or if any keys are missing, your *static* default is returned.
For example:
>>> kw = dict(first=u'John', department=u'Engineering')
>>> login.get_default(**kw)
u'my-static-login-default'
"""
if self.default_from is not None:
default = self.default_from(**kw)
if default is not None:
try:
return self.convert(self.normalize(default))
except StandardError:
pass
return self.default
json_exclude_attrs = (
'alwaysask', 'autofill', 'cli_name', 'cli_short_name', 'csv',
'sortorder', 'falsehoods', 'truths', 'version',
)
def __json__(self):
json_dict = {}
for (a, k, d) in self.kwargs:
if a in self.json_exclude_attrs:
continue
if k in (callable, DefaultFrom):
continue
elif isinstance(getattr(self, a), frozenset):
json_dict[a] = [k for k in getattr(self, a, [])]
else:
val = getattr(self, a, '')
if val is None or val is False:
# ignore False and not set because lack of their presence is
# the information itself
continue;
json_dict[a] = json_serialize(val)
json_dict['class'] = self.__class__.__name__
json_dict['name'] = self.name
json_dict['type'] = self.type.__name__
return json_dict
class Bool(Param):
"""
A parameter for boolean values (stored in the ``bool`` type).
"""
type = bool
type_error = _('must be True or False')
# FIXME: This my quick hack to get some UI stuff working, change these defaults
# --jderose 2009-08-28
kwargs = Param.kwargs + (
('truths', frozenset, frozenset([1, u'1', True, u'true', u'TRUE'])),
('falsehoods', frozenset, frozenset([0, u'0', False, u'false', u'FALSE'])),
)
def _convert_scalar(self, value, index=None):
"""
Convert a single scalar value.
"""
if type(value) in self.allowed_types:
return value
if isinstance(value, basestring):
value = value.lower()
if value in self.truths:
return True
if value in self.falsehoods:
return False
if type(value) in (tuple, list):
raise ConversionError(name=self.name, index=index,
error=ugettext(self.scalar_error))
raise ConversionError(name=self.name, index=index,
error=ugettext(self.type_error),
)
class Flag(Bool):
"""
A boolean parameter that always gets filled in with a default value.
This `Bool` subclass forces ``autofill=True`` in `Flag.__init__()`. If no
default is provided, it also fills in a default value of ``False``.
Lastly, unlike the `Bool` class, the default must be either ``True`` or
``False`` and cannot be ``None``.
For example:
>>> flag = Flag('my_flag')
>>> (flag.autofill, flag.default)
(True, False)
To have a default value of ``True``, create your `Flag` intance with
``default=True``. For example:
>>> flag = Flag('my_flag', default=True)
>>> (flag.autofill, flag.default)
(True, True)
Also note that creating a `Flag` instance with ``autofill=False`` will have
no effect. For example:
>>> flag = Flag('my_flag', autofill=False)
>>> flag.autofill
True
"""
def __init__(self, name, *rules, **kw):
kw['autofill'] = True
if 'default' not in kw:
kw['default'] = False
if type(kw['default']) is not bool:
default = kw['default']
raise TypeError(
TYPE_ERROR % ('default', bool, default, type(default))
)
super(Flag, self).__init__(name, *rules, **kw)
class Number(Param):
"""
Base class for the `Int` and `Decimal` parameters.
"""
def _convert_scalar(self, value, index=None):
"""
Convert a single scalar value.
"""
if type(value) in self.allowed_types:
return value
if type(value) in (unicode, int, long, float):
try:
return self.type(value)
except ValueError:
pass
if type(value) in (tuple, list):
raise ConversionError(name=self.name, index=index,
error=ugettext(self.scalar_error))
raise ConversionError(name=self.name, index=index,
error=ugettext(self.type_error),
)
class Int(Number):
"""
A parameter for integer values (stored in the ``int`` type).
"""
type = int
allowed_types = int, long
type_error = _('must be an integer')
kwargs = Param.kwargs + (
('minvalue', (int, long), int(MININT)),
('maxvalue', (int, long), int(MAXINT)),
)
@staticmethod
def convert_int(value):
if type(value) in Int.allowed_types:
return value
if type(value) is float:
return int(value)
if type(value) is unicode:
if u'.' in value:
return int(float(value))
return int(value, 0)
raise ValueError(value)
def __init__(self, name, *rules, **kw):
super(Int, self).__init__(name, *rules, **kw)
if (self.minvalue > self.maxvalue) and (self.minvalue is not None and self.maxvalue is not None):
raise ValueError(
'%s: minvalue > maxvalue (minvalue=%r, maxvalue=%r)' % (
self.nice, self.minvalue, self.maxvalue)
)
def _convert_scalar(self, value, index=None):
"""
Convert a single scalar value.
"""
try:
return Int.convert_int(value)
except ValueError:
raise ConversionError(name=self.get_param_name(),
index=index,
error=ugettext(self.type_error))
def _rule_minvalue(self, _, value):
"""
Check min constraint.
"""
assert type(value) in (int, long)
if value < self.minvalue:
return _('must be at least %(minvalue)d') % dict(
minvalue=self.minvalue,
)
def _rule_maxvalue(self, _, value):
"""
Check max constraint.
"""
assert type(value) in (int, long)
if value > self.maxvalue:
return _('can be at most %(maxvalue)d') % dict(
maxvalue=self.maxvalue,
)
class Decimal(Number):
"""
A parameter for floating-point values (stored in the ``Decimal`` type).
Python Decimal type helps overcome problems tied to plain "float" type,
e.g. problem with representation or value comparison. In order to safely
transfer the value over RPC libraries, it is being converted to string
which is then converted back to Decimal number.
"""
type = decimal.Decimal
type_error = _('must be a decimal number')
kwargs = Param.kwargs + (
('minvalue', decimal.Decimal, None),
('maxvalue', decimal.Decimal, None),
# round Decimal to given precision
('precision', int, None),
# when False, number is normalized to non-exponential form
('exponential', bool, False),
# set of allowed decimal number classes
('numberclass', tuple, ('-Normal', '+Zero', '+Normal')),
)
def __init__(self, name, *rules, **kw):
for kwparam in ('minvalue', 'maxvalue', 'default'):
value = kw.get(kwparam)
if value is None:
continue
if isinstance(value, (basestring, float)):
try:
value = decimal.Decimal(value)
except Exception, e:
raise ValueError(
'%s: cannot parse kwarg %s: %s' % (
name, kwparam, str(e)))
kw[kwparam] = value
super(Decimal, self).__init__(name, *rules, **kw)
if (self.minvalue > self.maxvalue) \
and (self.minvalue is not None and \
self.maxvalue is not None):
raise ValueError(
'%s: minvalue > maxvalue (minvalue=%s, maxvalue=%s)' % (
self.nice, self.minvalue, self.maxvalue)
)
if self.precision is not None and self.precision < 0:
raise ValueError('%s: precision must be at least 0' % self.nice)
def _rule_minvalue(self, _, value):
"""
Check min constraint.
"""
assert type(value) is decimal.Decimal
if value < self.minvalue:
return _('must be at least %(minvalue)s') % dict(
minvalue=self.minvalue,
)
def _rule_maxvalue(self, _, value):
"""
Check max constraint.
"""
assert type(value) is decimal.Decimal
if value > self.maxvalue:
return _('can be at most %(maxvalue)s') % dict(
maxvalue=self.maxvalue,
)
def _enforce_numberclass(self, value):
numberclass = value.number_class()
if numberclass not in self.numberclass:
raise ValidationError(name=self.get_param_name(),
error=_("number class '%(cls)s' is not included in a list "
"of allowed number classes: %(allowed)s") \
% dict(cls=numberclass,
allowed=u', '.join(self.numberclass))
)
def _enforce_precision(self, value):
assert type(value) is decimal.Decimal
if self.precision is not None:
quantize_exp = decimal.Decimal(10) ** -self.precision
try:
value = value.quantize(quantize_exp)
except decimal.DecimalException, e:
raise ConversionError(name=self.get_param_name(),
error=unicode(e))
return value
def _remove_exponent(self, value):
assert type(value) is decimal.Decimal
if not self.exponential:
try:
# adopted from http://docs.python.org/library/decimal.html
value = value.quantize(decimal.Decimal(1)) \
if value == value.to_integral() \
else value.normalize()
except decimal.DecimalException, e:
raise ConversionError(name=self.get_param_name(),
error=unicode(e))
return value
def _test_and_normalize(self, value):
"""
This method is run in conversion and normalization methods to test
that the Decimal number conforms to Parameter boundaries and then
normalizes the value.
"""
self._enforce_numberclass(value)
value = self._remove_exponent(value)
value = self._enforce_precision(value)
return value
def _convert_scalar(self, value, index=None):
if isinstance(value, (basestring, float)):
try:
value = decimal.Decimal(value)
except decimal.DecimalException, e:
raise ConversionError(name=self.get_param_name(), index=index,
error=unicode(e))
if isinstance(value, decimal.Decimal):
return self._test_and_normalize(value)
return super(Decimal, self)._convert_scalar(value, index)
def _normalize_scalar(self, value):
if isinstance(value, decimal.Decimal):
return self._test_and_normalize(value)
return super(Decimal, self)._normalize_scalar(value)
class Data(Param):
"""
Base class for the `Bytes` and `Str` parameters.
Previously `Str` was as subclass of `Bytes`. Now the common functionality
has been split into this base class so that ``isinstance(foo, Bytes)`` wont
be ``True`` when ``foo`` is actually an `Str` instance (which is confusing).
"""
kwargs = Param.kwargs + (
('minlength', int, None),
('maxlength', int, None),
('length', int, None),
('pattern', (basestring,), None),
('pattern_errmsg', (basestring,), None),
)
re = None
re_errmsg = None
def __init__(self, name, *rules, **kw):
super(Data, self).__init__(name, *rules, **kw)
if not (
self.length is None or
(self.minlength is None and self.maxlength is None)
):
raise ValueError(
'%s: cannot mix length with minlength or maxlength' % self.nice
)
if self.minlength is not None and self.minlength < 1:
raise ValueError(
'%s: minlength must be >= 1; got %r' % (self.nice, self.minlength)
)
if self.maxlength is not None and self.maxlength < 1:
raise ValueError(
'%s: maxlength must be >= 1; got %r' % (self.nice, self.maxlength)
)
if None not in (self.minlength, self.maxlength):
if self.minlength > self.maxlength:
raise ValueError(
'%s: minlength > maxlength (minlength=%r, maxlength=%r)' % (
self.nice, self.minlength, self.maxlength)
)
elif self.minlength == self.maxlength:
raise ValueError(
'%s: minlength == maxlength; use length=%d instead' % (
self.nice, self.minlength)
)
def _rule_pattern(self, _, value):
"""
Check pattern (regex) contraint.
"""
assert type(value) in self.allowed_types
if self.re.match(value) is None:
if self.re_errmsg:
return self.re_errmsg % dict(pattern=self.pattern,)
else:
return _('must match pattern "%(pattern)s"') % dict(
pattern=self.pattern,
)
class Bytes(Data):
"""
A parameter for binary data (stored in the ``str`` type).
This class is named *Bytes* instead of *Str* so it's aligned with the
Python v3 ``(str, unicode) => (bytes, str)`` clean-up. See:
http://docs.python.org/3.0/whatsnew/3.0.html
Also see the `Str` parameter.
"""
type = str
type_error = _('must be binary data')
def __init__(self, name, *rules, **kw):
if kw.get('pattern', None) is None:
self.re = None
else:
self.re = re.compile(kw['pattern'])
self.re_errmsg = kw.get('pattern_errmsg', None)
super(Bytes, self).__init__(name, *rules, **kw)
def _rule_minlength(self, _, value):
"""
Check minlength constraint.
"""
assert type(value) is str
if len(value) < self.minlength:
return _('must be at least %(minlength)d bytes') % dict(
minlength=self.minlength,
)
def _rule_maxlength(self, _, value):
"""
Check maxlength constraint.
"""
assert type(value) is str
if len(value) > self.maxlength:
return _('can be at most %(maxlength)d bytes') % dict(
maxlength=self.maxlength,
)
def _rule_length(self, _, value):
"""
Check length constraint.
"""
assert type(value) is str
if len(value) != self.length:
return _('must be exactly %(length)d bytes') % dict(
length=self.length,
)
def _convert_scalar(self, value, index=None):
if isinstance(value, unicode):
try:
value = base64.b64decode(value)
except TypeError, e:
raise Base64DecodeError(reason=str(e))
return super(Bytes, self)._convert_scalar(value, index)
class Str(Data):
"""
A parameter for Unicode text (stored in the ``unicode`` type).
This class is named *Str* instead of *Unicode* so it's aligned with the
Python v3 ``(str, unicode) => (bytes, str)`` clean-up. See:
http://docs.python.org/3.0/whatsnew/3.0.html
Also see the `Bytes` parameter.
"""
kwargs = Data.kwargs + (
('noextrawhitespace', bool, True),
)
type = unicode
type_error = _('must be Unicode text')
def __init__(self, name, *rules, **kw):
if kw.get('pattern', None) is None:
self.re = None
else:
self.re = re.compile(kw['pattern'], re.UNICODE)
self.re_errmsg = kw.get('pattern_errmsg', None)
super(Str, self).__init__(name, *rules, **kw)
def _convert_scalar(self, value, index=None):
"""
Convert a single scalar value.
"""
if type(value) in self.allowed_types:
return value
if type(value) in (int, long, float, decimal.Decimal):
return self.type(value)
if type(value) in (tuple, list):
raise ConversionError(name=self.name, index=index,
error=ugettext(self.scalar_error))
raise ConversionError(name=self.name, index=index,
error=ugettext(self.type_error),
)
def _rule_noextrawhitespace(self, _, value):
"""
Do not allow leading/trailing spaces.
"""
assert type(value) is unicode
if self.noextrawhitespace is False:
return
if len(value) != len(value.strip()):
return _('Leading and trailing spaces are not allowed')
def _rule_minlength(self, _, value):
"""
Check minlength constraint.
"""
assert type(value) is unicode
if len(value) < self.minlength:
return _('must be at least %(minlength)d characters') % dict(
minlength=self.minlength,
)
def _rule_maxlength(self, _, value):
"""
Check maxlength constraint.
"""
assert type(value) is unicode
if len(value) > self.maxlength:
return _('can be at most %(maxlength)d characters') % dict(
maxlength=self.maxlength,
)
def _rule_length(self, _, value):
"""
Check length constraint.
"""
assert type(value) is unicode
if len(value) != self.length:
return _('must be exactly %(length)d characters') % dict(
length=self.length,
)
class IA5Str(Str):
"""
An IA5String per RFC 4517
"""
def __init__(self, name, *rules, **kw):
super(IA5Str, self).__init__(name, *rules, **kw)
def _convert_scalar(self, value, index=None):
if isinstance(value, basestring):
for i in xrange(len(value)):
if ord(value[i]) > 127:
raise ConversionError(name=self.get_param_name(),
index=index,
error=_('The character %(char)r is not allowed.') %
dict(char=value[i],)
)
return super(IA5Str, self)._convert_scalar(value, index)
class Password(Str):
"""
A parameter for passwords (stored in the ``unicode`` type).
"""
password = True
kwargs = Str.kwargs + (
('confirm', bool, True),
)
def _convert_scalar(self, value, index=None):
if isinstance(value, (tuple, list)) and len(value) == 2:
(p1, p2) = value
if p1 != p2:
raise PasswordMismatch(name=self.name, index=index)
value = p1
return super(Password, self)._convert_scalar(value, index)
class Enum(Param):
"""
Base class for parameters with enumerable values.
"""
kwargs = Param.kwargs + (
('values', tuple, tuple()),
)
def __init__(self, name, *rules, **kw):
super(Enum, self).__init__(name, *rules, **kw)
for (i, v) in enumerate(self.values):
if type(v) not in self.allowed_types:
n = '%s values[%d]' % (self.nice, i)
raise TypeError(
TYPE_ERROR % (n, self.type, v, type(v))
)
if len(self.values) < 1:
raise ValueError(
'%s: list of values must not be empty' % self.nice)
def _rule_values(self, _, value, **kw):
if value not in self.values:
if len(self.values) == 1:
return _("must be '%(value)s'") % dict(value=self.values[0])
else:
values = u', '.join("'%s'" % value for value in self.values)
return _('must be one of %(values)s') % dict(values=values)
class BytesEnum(Enum):
"""
Enumerable for binary data (stored in the ``str`` type).
"""
type = unicode
class StrEnum(Enum):
"""
Enumerable for Unicode text (stored in the ``unicode`` type).
For example:
>>> enum = StrEnum('my_enum', values=(u'One', u'Two', u'Three'))
>>> enum.validate(u'Two', 'cli') is None
True
>>> enum.validate(u'Four', 'cli')
Traceback (most recent call last):
...
ValidationError: invalid 'my_enum': must be one of 'One', 'Two', 'Three'
"""
type = unicode
class IntEnum(Enum):
"""
Enumerable for integer data (stored in the ``int`` type).
"""
type = int
allowed_types = int, long
type_error = Int.type_error
def _convert_scalar(self, value, index=None):
"""
Convert a single scalar value.
"""
try:
return Int.convert_int(value)
except ValueError:
raise ConversionError(name=self.get_param_name(),
index=index,
error=ugettext(self.type_error))
class Any(Param):
"""
A parameter capable of holding values of any type. For internal use only.
"""
type = object
def _convert_scalar(self, value, index=None):
return value
def _validate_scalar(self, value, index=None):
for rule in self.all_rules:
error = rule(ugettext, value)
if error is not None:
raise ValidationError(
name=self.name,
value=value,
index=index,
error=error,
rule=rule,
)
class File(Str):
"""
File parameter type.
Accepts file names and loads their content into the parameter value.
"""
kwargs = Data.kwargs + (
# valid for CLI, other backends (e.g. webUI) can ignore this
('stdin_if_missing', bool, False),
('noextrawhitespace', bool, False),
)
class AccessTime(Str):
"""
Access time parameter type.
Accepts values conforming to generalizedTime as defined in RFC 4517
section 3.3.13 without time zone information.
"""
def _check_HHMM(self, t):
if len(t) != 4:
raise ValueError('HHMM must be exactly 4 characters long')
if not t.isnumeric():
raise ValueError('HHMM non-numeric')
hh = int(t[0:2])
if hh < 0 or hh > 23:
raise ValueError('HH out of range')
mm = int(t[2:4])
if mm < 0 or mm > 59:
raise ValueError('MM out of range')
def _check_dotw(self, t):
if t.isnumeric():
value = int(t)
if value < 1 or value > 7:
raise ValueError('day of the week out of range')
elif t not in ('Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'):
raise ValueError('invalid day of the week')
def _check_dotm(self, t, month_num=1, year=4):
if not t.isnumeric():
raise ValueError('day of the month non-numeric')
value = int(t)
if month_num in (1, 3, 5, 7, 8, 10, 12):
if value < 1 or value > 31:
raise ValueError('day of the month out of range')
elif month_num in (4, 6, 9, 11):
if value < 1 or value > 30:
raise ValueError('day of the month out of range')
elif month_num == 2:
if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0):
if value < 1 or value > 29:
raise ValueError('day of the month out of range')
else:
if value < 1 or value > 28:
raise ValueError('day of the month out of range')
def _check_wotm(self, t):
if not t.isnumeric():
raise ValueError('week of the month non-numeric')
value = int(t)
if value < 1 or value > 6:
raise ValueError('week of the month out of range')
def _check_woty(self, t):
if not t.isnumeric():
raise ValueError('week of the year non-numeric')
value = int(t)
if value < 1 or value > 52:
raise ValueError('week of the year out of range')
def _check_doty(self, t):
if not t.isnumeric():
raise ValueError('day of the year non-numeric')
value = int(t)
if value < 1 or value > 365:
raise ValueError('day of the year out of range')
def _check_month_num(self, t):
if not t.isnumeric():
raise ValueError('month number non-numeric')
value = int(t)
if value < 1 or value > 12:
raise ValueError('month number out of range')
def _check_interval(self, t, check_func):
intervals = t.split(',')
for i in intervals:
if not i:
raise ValueError('invalid time range')
values = i.split('-')
if len(values) > 2:
raise ValueError('invalid time range')
for v in values:
check_func(v)
if len(values) == 2:
if int(values[0]) > int(values[1]):
raise ValueError('invalid time range')
def _check_W_spec(self, ts, index):
if ts[index] != 'day':
raise ValueError('invalid week specifier')
index += 1
self._check_interval(ts[index], self._check_dotw)
return index
def _check_M_spec(self, ts, index):
if ts[index] == 'week':
self._check_interval(ts[index + 1], self._check_wotm)
index = self._check_W_spec(ts, index + 2)
elif ts[index] == 'day':
index += 1
self._check_interval(ts[index], self._check_dotm)
else:
raise ValueError('invalid month specifier')
return index
def _check_Y_spec(self, ts, index):
if ts[index] == 'month':
index += 1
self._check_interval(ts[index], self._check_month_num)
month_num = int(ts[index])
index = self._check_M_spec(ts, index + 1)
elif ts[index] == 'week':
self._check_interval(ts[index + 1], self._check_woty)
index = self._check_W_spec(ts, index + 2)
elif ts[index] == 'day':
index += 1
self._check_interval(ts[index], self._check_doty)
else:
raise ValueError('invalid year specifier')
return index
def _check_generalized(self, t):
assert type(t) is unicode
if len(t) not in (10, 12, 14):
raise ValueError('incomplete generalized time')
if not t.isnumeric():
raise ValueError('time non-numeric')
# don't check year value, with time travel and all :)
self._check_month_num(t[4:6])
year_num = int(t[0:4])
month_num = int(t[4:6])
self._check_dotm(t[6:8], month_num, year_num)
if len(t) >= 12:
self._check_HHMM(t[8:12])
else:
self._check_HHMM('%s00' % t[8:10])
if len(t) == 14:
s = int(t[12:14])
if s < 0 or s > 60:
raise ValueError('seconds out of range')
def _check(self, time):
ts = time.split()
if ts[0] == 'absolute':
if len(ts) != 4:
raise ValueError('invalid format, must be \'absolute generalizedTime ~ generalizedTime\'')
self._check_generalized(ts[1])
if ts[2] != '~':
raise ValueError('invalid time range separator')
self._check_generalized(ts[3])
if int(ts[1]) >= int(ts[3]):
raise ValueError('invalid time range')
elif ts[0] == 'periodic':
index = None
if ts[1] == 'yearly':
index = self._check_Y_spec(ts, 2)
elif ts[1] == 'monthly':
index = self._check_M_spec(ts, 2)
elif ts[1] == 'weekly':
index = self._check_W_spec(ts, 2)
elif ts[1] == 'daily':
index = 1
if index is None:
raise ValueError('period must be yearly, monthy or daily, got \'%s\'' % ts[1])
self._check_interval(ts[index + 1], self._check_HHMM)
else:
raise ValueError('time neither absolute or periodic')
def _rule_required(self, _, value):
try:
self._check(value)
except ValueError, e:
raise ValidationError(name=self.get_param_name(), error=e.args[0])
except IndexError:
raise ValidationError(
name=self.get_param_name(), error=ugettext('incomplete time value')
)
return None
class DNParam(Param):
type = DN
def _convert_scalar(self, value, index=None):
"""
Convert a single scalar value.
"""
if type(value) in self.allowed_types:
return value
try:
dn = DN(value)
except Exception, e:
raise ConversionError(name=self.get_param_name(), index=index,
error=ugettext(e))
return dn
class DeprecatedParam(Any):
kwargs = Param.kwargs + (
('deprecate', bool, True),
)
def __init__(self, name, *rules, **kw):
if 'flags' in kw:
kw['flags'] = list(kw['flags']) + ['no_option']
else:
kw['flags'] = ['no_option']
super(DeprecatedParam, self).__init__(name, *rules, **kw)
def _rule_deprecate(self, _, value):
return _('this option is deprecated')
def create_param(spec):
"""
Create an `Str` instance from the shorthand ``spec``.
This function allows you to create `Str` parameters (the most common) from
a convenient shorthand that defines the parameter name, whether it is
required, and whether it is multivalue. (For the definition of the
shorthand syntax, see the `parse_param_spec()` function.)
If ``spec`` is an ``str`` instance, it will be used to create a new `Str`
parameter, which will be returned. For example:
>>> s = create_param('hometown?')
>>> s
Str('hometown?')
>>> (s.name, s.required, s.multivalue)
('hometown', False, False)
On the other hand, if ``spec`` is already a `Param` instance, it is
returned unchanged. For example:
>>> b = Bytes('cert')
>>> create_param(b) is b
True
As a plugin author, you will not call this function directly (which would
be no more convenient than simply creating the `Str` instance). Instead,
`frontend.Command` will call it for you when it evaluates the
``takes_args`` and ``takes_options`` attributes, and `frontend.Object`
will call it for you when it evaluates the ``takes_params`` attribute.
:param spec: A spec string or a `Param` instance.
"""
if isinstance(spec, Param):
return spec
if type(spec) is not str:
raise TypeError(
TYPE_ERROR % ('spec', (str, Param), spec, type(spec))
)
return Str(spec)