A comparison of outputs reveals differences:
user@user-VirtualBox:~$ pip list feedparser (5.1.3) pip (1.4.1) setuptools (1.1.5) wsgiref (0.1.2) user@user-VirtualBox:~$ pip freeze feedparser==5.1.3 wsgiref==0.1.2 Pip's documentation states
freeze Output installed packages in requirements format. list List installed packages. but what is "requirements format," and why does pip list generate a more comprehensive list than pip freeze?
When you are using a virtualenv, you can specify a requirements.txt file to install all the dependencies.
A typical usage:
$ pip install -r requirements.txt The packages need to be in a specific format for pip to understand, which is
feedparser==5.1.3 wsgiref==0.1.2 django==1.4.2 ... That is the "requirements format".
Here, django==1.4.2 implies install django version 1.4.2 (even though the latest is 1.6.x). If you do not specify ==1.4.2, the latest version available would be installed.
You can read more in "Virtualenv and pip Basics", and the official "Requirements File Format" documentation.
To answer the second part of this question, the two packages shown in pip list but not pip freeze are setuptools (which is easy_install) and pip itself.
It looks like pip freeze just doesn't list packages that pip itself depends on. You may use the --all flag to show also those packages.
From the documentation:
--allDo not skip these packages in the output: pip, setuptools, distribute, wheel
Look at the pip documentation, which describes the functionality of both as:
pip list
List installed packages, including editables.
pip freeze
Output installed packages in requirements format.
So there are two differences:
Output format, freeze gives us the standard requirement format that may be used later with pip install -r to install requirements from.
Output content, pip list include editables which pip freeze does not.
The main difference is that the output of pip freeze can be dumped into a requirements.txt file and used later to re-construct the "frozen" environment.
In other words you can run: pip freeze > frozen-requirements.txt on one machine and then later on a different machine or on a clean environment you can do: pip install -r frozen-requirements.txt and you'll get the an identical environment with the exact same dependencies installed as you had in the original environment where you generated the frozen-requirements.txt.