pip broke. how to fix DistributionNotFound error?

Question

I find this problem in my MacBook, the reason is because as @Stephan said, I use easy_install to install pip, and the mixture of both py package manage tools led to the pkg_resources.DistributionNotFound problem. The resolve is:

easy_install --upgrade pip

Remember: just use one of the above tools to manage your Py packages.

I replaced 0.8.1 in 0.8.2 in /usr/local/bin/pip and everything worked again.

__requires__ = 'pip==0.8.2'
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.exit(
        load_entry_point('pip==0.8.2', 'console_scripts', 'pip')()
    )

I installed pip through easy_install which probably caused me this headache. I think this is how you should do it nowadays..

$ sudo apt-get install python-pip python-dev build-essential 
$ sudo pip install --upgrade pip 
$ sudo pip install --upgrade virtualenv

I had this issue when I was using homebrew. Here is the solution from Issue #26900

python -m pip install --upgrade --force pip

Try re-installing with the get-pip script:

wget https://bootstrap.pypa.io/get-pip.py
sudo python3 get-pip.py

This is sourced from the pip Github page, and worked for me.

If you're on CentOS make sure you have the YUM package "python-setuptools" installed

yum install python-setuptools

Fixed it for me.

The root of the problem are often outdated scripts in the bin (Linux) or Scripts (Windows) subdirectory. I'll explain this using problem I encountered myself as an example.

I had virtualenv version 1.10 installed in my user site-packages (the fact it's in user site-packages not sytem site-packages is irrelevant here)

pdobrogost@host:~$ which virtualenv
/home/users/pdobrogost/.local/bin/virtualenv
pdobrogost@host:~$ virtualenv --version
1.10

After I upgraded it to version 1.11 I got the following error:

pdobrogost@host:~$ virtualenv --version  
Traceback (most recent call last):   
  File "/home/users/pdobrogost/.local/bin/virtualenv", line 5, in <module>
    from pkg_resources import load_entry_point   
File "build/bdist.linux-x86_64/egg/pkg_resources.py", line 2701, in <module>
    return self.__dep_map   
File "build/bdist.linux-x86_64/egg/pkg_resources.py", line 572, in resolve
    if insert: 
pkg_resources.DistributionNotFound: virtualenv==1.10

File /home/users/pdobrogost/.local/bin/virtualenv mentioned in the error message looked like this:

#!/opt/python/2.7.5/bin/python2.7
# EASY-INSTALL-ENTRY-SCRIPT: 'virtualenv==1.10','console_scripts','virtualenv'
__requires__ = 'virtualenv==1.10'
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.exit(
        load_entry_point('virtualenv==1.10', 'console_scripts', 'virtualenv')()
    ) 

There, we see that virtualenv script was not updated and still requires previously installed version 1.10 of virtualenv.
Now, reinstalling virtualenv like this

pdobrogost@host:~$ pip install --user --upgrade virtualenv
Downloading/unpacking virtualenv from https://pypi.python.org/packages/py27/v/virtualenv/virtualenv-1.11.1-py27-none-any.whl#md5=265770b61de41d34d2e9fdfddcdf034c
  Using download cache from /home/users/pdobrogost/.pip_download_cache/https%3A%2F%2Fpypi.python.org%2Fpackages%2Fpy27%2Fv%2Fvirtualenv%2Fvirtualenv-1.11.1-py27-none-any.whl
Installing collected packages: virtualenv
Successfully installed virtualenv
Cleaning up...

does not help (neither pip install --user --upgrade --force-reinstall virtualenv) because script /home/users/pdobrogost/.local/bin/virtualenv is left unchanged.

The only way I could fix this was by manually removing virtualenv* scripts from /home/users/pdobrogost/.local/bin/ folder and installing virtualenv again. After this, newly generated scripts refer to the proper version of the package:

pdobrogost@host:~$ virtualenv --version
1.11

I was able to resolve this like so:

$ brew update
$ brew doctor
$ brew uninstall python
$ brew install python --build-from-source    # took ~5 mins
$ python --version                           # => Python 2.7.9
$ pip install --upgrade pip

I'm running w/ the following stuff (as of Jan 2, 2015):

OS X Yosemite
Version 10.10.1

$ brew -v
Homebrew 0.9.5

$ python --version
Python 2.7.9

$ ipython --version
2.2.0

$ pip --version
pip 6.0.3 from /usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-6.0.3-py2.7.egg (python 2.7)

$ which pip
/usr/local/bin/pip