After updating pip, I get SyntaxError: invalid syntax when trying to install speedtest-cli

Question

I'm trying to use pip to install speedtest-cli package on centOS 6. but after that I updated the pip, I'm getting this Syntax error and I could not use pip anymore.

    Traceback (most recent call last):
  File "/usr/bin/pip", line 7, in <module>
    from pip._internal.cli.main import main
  File "/usr/lib/python2.6/site-packages/pip/_internal/cli/main.py", line 10, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/usr/lib/python2.6/site-packages/pip/_internal/cli/autocompletion.py", line 9, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/usr/lib/python2.6/site-packages/pip/_internal/cli/main_parser.py", line 7, in <module>
    from pip._internal.cli import cmdoptions
  File "/usr/lib/python2.6/site-packages/pip/_internal/cli/cmdoptions.py", line 104
    binary_only = FormatControl(set(), {':all:'})
                                               ^
SyntaxError: invalid syntax

I also tried to remove pip using pip uninstall pip but it didn't work either. Please help if you know a solution. Thanks in advance