diff --git a/sphinx/ext/doctest.py b/sphinx/ext/doctest.py
index cd35e789a..d0614718b 100644
--- a/sphinx/ext/doctest.py
+++ b/sphinx/ext/doctest.py
@@ -15,7 +15,6 @@ import re
 import sys
 import time
 import codecs
-import platform
 from os import path
 import doctest
 
@@ -144,7 +143,8 @@ class TestDirective(Directive):
         if self.name == 'doctest' and 'pyversion' in self.options:
             try:
                 spec = self.options['pyversion']
-                if not is_allowed_version(spec, platform.python_version()):
+                python_version = '.'.join(str(v) for v in sys.version_info[:3])
+                if not is_allowed_version(spec, python_version):
                     flag = doctest.OPTIONFLAGS_BY_NAME['SKIP']
                     node['options'][flag] = True  # Skip the test
             except InvalidSpecifier:
diff --git a/sphinx/util/inspect.py b/sphinx/util/inspect.py
index 5ed39906e..fd13d6fd6 100644
--- a/sphinx/util/inspect.py
+++ b/sphinx/util/inspect.py
@@ -453,7 +453,8 @@ class Signature(object):
 
         if annotation.__module__ == 'builtins':
             return annotation.__qualname__  # type: ignore
-        elif isinstance(annotation, typing.GenericMeta):
+        elif (hasattr(typing, 'GenericMeta') and  # for py36 or below
+              isinstance(annotation, typing.GenericMeta)):
             # In Python 3.5.2+, all arguments are stored in __args__,
             # whereas __parameters__ only contains generic parameters.
             #
@@ -480,7 +481,8 @@ class Signature(object):
             if params is not None:
                 param_str = ', '.join(self.format_annotation(p) for p in params)
                 return '%s[%s]' % (qualified_name, param_str)
-        elif (isinstance(annotation, typing.CallableMeta) and  # type: ignore
+        elif (hasattr(typing, 'CallableMeta') and  # for py36 or below
+              isinstance(annotation, typing.CallableMeta) and  # type: ignore
               getattr(annotation, '__args__', None) is not None and
               hasattr(annotation, '__result__')):
             # Skipped in the case of plain typing.Callable
@@ -495,7 +497,8 @@ class Signature(object):
             return '%s[%s, %s]' % (qualified_name,
                                    args_str,
                                    self.format_annotation(annotation.__result__))
-        elif (isinstance(annotation, typing.TupleMeta) and  # type: ignore
+        elif (hasattr(typing, 'TupleMeta') and  # for py36 or below
+              isinstance(annotation, typing.TupleMeta) and  # type: ignore
               hasattr(annotation, '__tuple_params__') and
               hasattr(annotation, '__tuple_use_ellipsis__')):
             params = annotation.__tuple_params__
diff --git a/tests/test_ext_math.py b/tests/test_ext_math.py
index 9bbd6217d..1cdf4d637 100644
--- a/tests/test_ext_math.py
+++ b/tests/test_ext_math.py
@@ -11,6 +11,7 @@
 
 import os
 import re
+import errno
 import subprocess
 
 import pytest
@@ -20,7 +21,7 @@ def has_binary(binary):
     try:
         subprocess.check_output([binary])
     except OSError as e:
-        if e.errno == os.errno.ENOENT:
+        if e.errno == errno.ENOENT:
             # handle file not found error.
             return False
         else:
diff --git a/tests/test_util_inspect.py b/tests/test_util_inspect.py
index b5d50ed71..136536ec6 100644
--- a/tests/test_util_inspect.py
+++ b/tests/test_util_inspect.py
@@ -215,7 +215,12 @@ def test_Signature_annotations():
 
     # TypeVars and generic types with TypeVars
     sig = inspect.Signature(f2).format_args()
-    assert sig == '(x: List[T], y: List[T_co], z: T) -> List[T_contra]'
+    if sys.version_info < (3, 7):
+        sig == ('(x: typing.List[T], y: typing.List[T_co], z: T) -> '
+                'typing.List[T_contra]')
+    else:
+        sig == ('(x: typing.List[~T], y: typing.List[+T_co], z: T) -> '
+                'typing.List[-T_contra]')
 
     # Union types
     sig = inspect.Signature(f3).format_args()