Python 2.6 support is officially deprecated.

pkg/mac/README.txt

@@ -4,7 +4,7 @@ Building pgAdmin4.dmg on Mac OS X
 Required Packages (Either build the sources or get them from macports or similar):
 
 1. Python installation
-  - Python 2.6 or above from https://www.python.org/
+  - Python 2.7 or 3.4+ or above from https://www.python.org/
 
 2. QT installation
   - Qt 4 or 5 from http://www.qt.io/

pkg/pip/setup_pip.py

@@ -110,7 +110,7 @@ setup(
         ]
     },
 
-    # Specify data files to be included. For Python 2.6 include them in MANIFEST.in
+    # Specify data files to be included.
     ##package_data="",
 
     # To package data files outside package directory.

pkg/win32/README.txt

@@ -4,7 +4,7 @@
 To generate a pgAdmin 4 installer for Windows bit, the following packages must be installed:
 
 1. Python installation
-  - Python 2.6 or above from https://www.python.org/
+  - Python 2.7 or 3.4+ or above from https://www.python.org/
 
 2. QT installation
   - Qt 4.6 through 5.5 from http://www.qt.io/