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How to add git source in requirements.txt

I would like to install a certain package from a private git repository. This is possible using pip install git+<REPO_LINK>. However, I would like to pip install -r requirements.txt all of my packages at the same time without having to specify which one comes from Pypi and private repo.
I have tried adding a configuration in ~/.config/pip/pip.conf
[global]
find-links =
git+<REPO_LINK>
but this happened when running pip install -r requirements.txt:
ERROR: Could not find a version that satisfies the requirement my-package==0.1
Thanks in advance.

I have found a solution for it at this doc.
pip install git+<REPO_LINK>#egg=<PACKAGE_NAME>
When I run pip freeze, the package I have just installed is printed like this:
git+<REPO_LINK>#egg=<PACKAGE_NAME>
Add it to your requirements.txt so pip install -r requirements.txt install this specific package so as public ones from Pypi.
:)

Why use pip install requirements.txt instead of pip install ./?

I'm not very experienced with dependency management in Python but it seems that all of the dependencies in requirements.txt could alternatively be placed in the setup.py file under the install_requires field as follows:
setup(
...
install_requires=['numpy=1.2.3', 'pandas=1.2.3']
...
)
Since pip install ./ using a setup.py file also provides lots of additional functionality compared to pip install -r requirements.txt, what is the use for the latter? Would a project ever have a valid reason to use both?

pip install . installs your custom package with all its dependencies. pip install -r requirements.txt installs only the dependencies.

You could also add -e . to your requirements.txt and install your package with pip install -r requirements.txt

How to install package via pip requirements.txt from VCS into current directory?

For example, we have project Foo with dependency Bar (that in private Git repo) and we want install Bar into Foo directory via pip from requirements.txt.
We can manually install Bar with console command:
pip install --target=. git+ssh://git.repo/some_pkg.git#egg=SomePackage
But how to install Bar into current directory from requirements.txt?

The best way to do this would be to clone the repository, or just donwload the requirements.txt file, and then run pip install -r requirements.txt to install all the modules dependencies.

You can use the "editable" syntax in requirements.txt to install a package from a VCS (eg git)
From the docs:
pip install -e git+https://git.repo/some_pkg.git#egg=SomeProject

What does " -r " do in pip install -r requirements.txt

I looked up how to install multiple packages from a requirements document using pip. The answers were mostly:
pip install -r requirements.txt
What does the -r do though? I can't find an answer for this and it isn't listed when I run pip help.

Instead of pip --help, look into pip install --help:
-r, --requirement Install from the given requirements
file. This option can be used multiple
times.
Also see these documentation paragraphs:
pip install
Requirements Files.

-r will search for requirement file.
pip install --help
will help you !!

May, 2022 Update:
If you run this command below without "-r":
pip install requirements.txt
You will get this error below:
ERROR: Could not find a version that satisfies the requirement requirements.txt (from versions: none)
HINT: You are attempting to install a package literally named "requirements.txt" (which cannot exist). Consider using the '-r' flag to install the packages listed in requirements.txt
ERROR: No matching distribution found for requirements.txt
Because "pip" tries to install the package "requirements.txt" instead of installing the packages listed in "requirements.txt". Of cource, the package "requirements.txt" doesn't exist in PyPI while for example, the packages "django" and "pillow" exist in PyPI:
pip install django
pip install pillow
So, to install the packages listed in "requirements.txt", you must need "-r";
pip install -r requirements.txt
You can check what "-r" means by running the command below:
pip install --help
-r, --requirement Install from the given requirements file. This option can be used multiple times.

In your case pip install -r requirements.txt will install the libraries listed in your requirements.txt file.

pip install requirements.txt
Above statement looks for a python package named requirements.txt. No such package exists. Your intention is that pip install opens the txt and reads the packages from there. The -r allows pip install to open requirements.txt and install the packages inside of it instead.

PIP: Installing only the dependencies

I have a script that creates a virtualenv, installs distribute and pip in it and then optionally clones a git repo.
Now I have the project I will be working on, installed. But its dependencies are not installed. How can I make pip install all the dependencies as if I have issued a pip install MyApp?
EDIT: Appareantly my question is a duplicate of this one.
Not exactly sure but pip install -e . seems to do what I want without too many extra stuff lying around. I'd prefer if my code wasn't linked from site-packages though.

If your dependencies are defined in the setup.py file, you can first dump them to an external file using:
python setup.py egg_info
This will list all your dependencies in YOUR_PROJECT.egg-info/requires.txt file. Then you can install them using pip:
pip install -r *.egg-info/requires.txt
to delete what you just created:
rm -rf *.egg-info/
to save some time copy pasting:
python setup.py egg_info
pip install -r *.egg-info/requires.txt
rm -rf *.egg-info/

In my package root issuing pip install -e . installs dependencies.

To install your project's dependencies (i.e. install_requires + extra_requires) you have to extract your dependencies using setuptools egg-info and then install the filtered list of the combined dependencies:
python setup.py egg_info
pip install `grep -v '^\[' *.egg-info/requires.txt`

You should use the pip requirements file.
Essentially, place all your requirements, one in each line in a file and pass that to pip using the command
pip install -r requirements.txt
What more, if you have a standard environment, pip can actually dump such a file from existing installs using the command:
pip freeze
You can put the file thus generated directly into the pip requirements, and call the previous command from your deployment script.
Pretty cool, isnt it? :)

You can use pip-tools to create a requirements.txt that only contains the dependencies of your package:
$ pip-compile -o requirements.txt setup.py
Note that the command above only works if you do not already have a requirements.txt file. If you happen to have one already, just delete it.
Using the generated requirements.txt you can then run pip to install the dependencies:
$ pip install -r requirements.txt
Bonus 1:
The requirements.txt will include comments that indicate where the regarding dependency originates from.
Bonus 2:
If you have have an extras_require section for optional dependencies in your setup.py that looks e.g. like this:
...
extras_require={
"development": [
"wheel",
"debugpy",
"pytest",
],
},
...
You can create the requirements.txt including the optional dependencies by using:
$ pip-compile -o requirements.txt --extra development setup.py