Why pip commands results in traceback and error SyntaxError: invalid syntax

Issue

• Running pip or any other commands result in the following Traceback

[root@example ~]# pip --version
Traceback (most recent call last):
  File "/usr/bin/pip", line 7, in <module>
    from pip._internal import main
  File "/usr/lib/python2.6/site-packages/pip/_internal/__init__.py", line 42, in <module>
    from pip._internal import cmdoptions
  File "/usr/lib/python2.6/site-packages/pip/_internal/cmdoptions.py", line 16, in <module>
    from pip._internal.index import (
  File "/usr/lib/python2.6/site-packages/pip/_internal/index.py", line 526
    {str(c.version) for c in all_candidates},
                      ^
SyntaxError: invalid syntax