Pip freeze vs. pip list

Question

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.

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.

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:

--all

Do 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:

1. Output format, freeze gives us the standard requirement format that may be used later with pip install -r to install requirements from.

2. Output content, pip list include editables which pip freeze does not.

pip list shows ALL installed packages.

pip freeze shows packages YOU installed via pip (or pipenv if using that tool) command in a requirements format.

Remark below that setuptools, pip, wheel are installed when pipenv shell creates my virtual envelope. These packages were NOT installed by me using pip:

test1 % pipenv shell
Creating a virtualenv for this project…
Pipfile: /Users/terrence/Development/Python/Projects/test1/Pipfile
Using /usr/local/Cellar/pipenv/2018.11.26_3/libexec/bin/python3.8 (3.8.1) to create virtualenv…
⠹ Creating virtual environment...
<SNIP>
Installing setuptools, pip, wheel...
done.
✔ Successfully created virtual environment! 
<SNIP>

Now review & compare the output of the respective commands where I've only installed cool-lib and sampleproject (of which peppercorn is a dependency):

test1 % pip freeze       <== Packages I'VE installed w/ pip

-e git+https://github.com/gdamjan/hello-world-python-package.git@10<snip>71#egg=cool_lib
peppercorn==0.6
sampleproject==1.3.1


test1 % pip list         <== All packages, incl. ones I've NOT installed w/ pip

Package       Version Location                                                                    
------------- ------- --------------------------------------------------------------------------
cool-lib      0.1  /Users/terrence/.local/share/virtualenvs/test1-y2Zgz1D2/src/cool-lib           <== Installed w/ `pip` command
peppercorn    0.6       <== Dependency of "sampleproject"
pip           20.0.2  
sampleproject 1.3.1     <== Installed w/ `pip` command
setuptools    45.1.0  
wheel         0.34.2