pip install errors out: SyntaxError: invalid syntax

Question

pip install does not work when trying to install virtualenv, requests or pex on CentOS6. I am on python2.6 and pip 9.0.1. Can anyone tell me why is this happening?

(pex_build)[root@pex pex_build]# pip install virtualenv

Output:

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

Command:

(pex_build) [root@pex pex_build]# pip install requests pex

Output:

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

Also curl gives the similar error, when trying to get get-pip.py

Command:

(pex_build) [root@pex pex_build]# curl https://bootstrap.pypa.io/get-pip.py | python



% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 1602k  100 1602k    0     0  7373k      0 --:--:-- --:--:-- --:--:-- 14.6M

Traceback (most recent call last):
  File "<stdin>", line 20636, in <module>
  File "<stdin>", line 197, in main
  File "<stdin>", line 82, in bootstrap
  File "/tmp/tmp5zrn_f/pip.zip/pip/_internal/__init__.py", line 42, in <module>
  File "/tmp/tmp5zrn_f/pip.zip/pip/_internal/cmdoptions.py", line 16, in <module>
  File "/tmp/tmp5zrn_f/pip.zip/pip/_internal/index.py", line 526
    {str(c.version) for c in all_candidates},
                      ^
SyntaxError: invalid syntax

Answer 1

pip works with CPython versions 2.7, 3.3, 3.4, 3.5, 3.6 and also pypy.

This means pip works on the latest patch version of each of these minor versions. Previous patch versions are supported on a best effort approach.

Just use below command one you upgrade to compatible Python version.

pip install requests

check pip-documentation for more details.

Including @eandersson's comments

Or you you can upgrade pip to 9.0.3

pip install pip==9.0.3

Answer 2

The problem is your version of pip is broken with Python 2.6. If you upgrade to 9.0.3 it should work again.

pip install pip==9.0.3

If you are unable to upgrade pip using pip, you could re-install the package as well using your local package manager, and then upgrade to pip 9.0.3.

Keep in mind that if you are using virtual environments it is recommended that you upgrade virtualenv as well so that your virtual environments will have pip 9.0.3 as well.

pip install virtualenv==15.2.0

Be careful though to not upgrade to a version of pip higher than 9.0.3 or virtualenv higher than 15.2.0 as Python 2.6 support was removed with those versions, as mentioned by Prateek.