I started working with Python. I've added requirements.txt and setup.py to my project. But, I am still confused about the purpose of both files. I have read that setup.py is designed for redistributable things and that requirements.txt is designed for non-redistributable things. But I am not certain this is accurate.
How are those two files truly intended to be used?
requirements.txt:
This helps you to set up your development environment.
Programs like pip can be used to install all packages listed in the file in one fell swoop. After that you can start developing your python script. Especially useful if you plan to have others contribute to the development or use virtual environments.
This is how you use it:
pip install -r requirements.txt
It can be produced easily by pip itself:
pip freeze > requirements.txt
pip automatically tries to only add packages that are not installed by default, so the produced file is pretty minimal.
setup.py:
This helps you to create packages that you can redistribute.
The setup.py script is meant to install your package on the end user's system, not to prepare the development environment as pip install -r requirements.txt does. See this answer for more details on setup.py.
The dependencies of your project are listed in both files.
The short answer is that requirements.txt is for listing package requirements only. setup.py on the other hand is more like an installation script. If you don't plan on installing the python code, typically you would only need requirements.txt.
The file setup.py describes, in addition to the package dependencies, the set of files and modules that should be packaged (or compiled, in the case of native modules (i.e., written in C)), and metadata to add to the python package listings (e.g. package name, package version, package description, author, ...).
Because both files list dependencies, this can lead to a bit of duplication. Read below for details.
requirements.txt
This file lists python package requirements. It is a plain text file (optionally with comments) that lists the package dependencies of your python project (one per line). It does not describe the way in which your python package is installed. You would generally consume the requirements file with pip install -r requirements.txt.
The filename of the text file is arbitrary, but is often requirements.txt by convention. When exploring source code repositories of other python packages, you might stumble on other names, such as dev-dependencies.txt or dependencies-dev.txt. Those serve the same purpose as dependencies.txt but generally list additional dependencies of interest to developers of the particular package, namely for testing the source code (e.g. pytest, pylint, etc.) before release. Users of the package generally wouldn't need the entire set of developer dependencies to run the package.
If multiplerequirements-X.txt variants are present, then usually one will list runtime dependencies, and the other build-time, or test dependencies. Some projects also cascade their requirements file, i.e. when one requirements file includes another file (example). Doing so can reduce repetition.
setup.py
This is a python script which uses the setuptools module to define a python package (name, files included, package metadata, and installation). It will, like requirements.txt, also list runtime dependencies of the package. Setuptools is the de-facto way to build and install python packages, but it has its shortcomings, which over time have sprouted the development of new "meta-package managers", like pip. Example shortcomings of setuptools are its inability to install multiple versions of the same package, and lack of an uninstall command.
When a python user does pip install ./pkgdir_my_module (or pip install my-module), pip will run setup.py in the given directory (or module). Similarly, any module which has a setup.py can be pip-installed, e.g. by running pip install . from the same folder.
Do I really need both?
Short answer is no, but it's nice to have both. They achieve different purposes, but they can both be used to list your dependencies.
There is one trick you may consider to avoid duplicating your list of dependencies between requirements.txt and setup.py. If you have written a fully working setup.py for your package already, and your dependencies are mostly external, you could consider having a simple requirements.txt with only the following:
# requirements.txt
#
# installs dependencies from ./setup.py, and the package itself,
# in editable mode
-e .
# (the -e above is optional). you could also just install the package
# normally with just the line below (after uncommenting)
# .
The -e is a special pip install option which installs the given package in editable mode. When pip -r requirements.txt is run on this file, pip will install your dependencies via the list in ./setup.py. The editable option will place a symlink in your install directory (instead of an egg or archived copy). It allows developers to edit code in place from the repository without reinstalling.
You can also take advantage of what's called "setuptools extras" when you have both files in your package repository. You can define optional packages in setup.py under a custom category, and install those packages from just that category with pip:
# setup.py
from setuptools import setup
setup(
name="FOO"
...
extras_require = {
'dev': ['pylint'],
'build': ['requests']
}
...
)
and then, in the requirements file:
# install packages in the [build] category, from setup.py
# (path/to/mypkg is the directory where setup.py is)
-e path/to/mypkg[build]
This would keep all your dependency lists inside setup.py.
Note: You would normally execute pip and setup.py from a sandbox, such as those created with the program virtualenv. This will avoid installing python packages outside the context of your project's development environment.
For the sake of completeness, here is how I see it in 3 4 different angles.
Their design purposes are different
This is the precise description quoted from the official documentation (emphasis mine):
Whereas install_requires (in setup.py) defines the dependencies for a single project, Requirements Files are often used to define the requirements for a complete Python environment.
Whereas install_requires requirements are minimal, requirements files often contain an exhaustive listing of pinned versions for the purpose of achieving repeatable installations of a complete environment.
But it might still not easy to be understood, so in next section, there come 2 factual examples to demonstrate how the 2 approaches are supposed to be used, differently.
Their actual usages are therefore (supposed to be) different
If your project foo is going to be released as a standalone library (meaning, others would probably do import foo), then you (and your downstream users) would want to have a flexible declaration of dependency, so that your library would not (and it must not) be "picky" about what exact version of YOUR dependencies should be. So, typically, your setup.py would contain lines like this:
install_requires=[
'A>=1,<2',
'B>=2'
]
If you just want to somehow "document" or "pin" your EXACT current environment for your application bar, meaning, you or your users would like to use your application bar as-is, i.e. running python bar.py, you may want to freeze your environment so that it would always behave the same. In such case, your requirements file would look like this:
A==1.2.3
B==2.3.4
# It could even contain some dependencies NOT strickly required by your library
pylint==3.4.5
In reality, which one do I use?
If you are developing an application bar which will be used by python bar.py, even if that is "just script for fun", you are still recommended to use requirements.txt because, who knows, next week (which happens to be Christmas) you would receive a new computer as a gift, so you would need to setup your exact environment there again.
If you are developing a library foo which will be used by import foo, you have to prepare a setup.py. Period.
But you may still choose to also provide a requirements.txt at the same time, which can:
(a) either be in the A==1.2.3 style (as explained in #2 above);
(b) or just contain a magical single .
.
The latter is essentially using the conventional requirements.txt habit to document your installation step is pip install ., which means to "install the requirements based on setup.py" while without duplication. Personally I consider this last approach kind of blurs the line, adds to the confusion, but it is nonetheless a convenient way to explicitly opt out for dependency pinning when running in a CI environment. The trick was derived from an approach mentioned by Python packaging maintainer Donald in his blog post.
Different lower bounds.
Assuming there is an existing engine library with this history:
engine 1.1.0 Use steam
...
engine 1.2.0 Internal combustion is invented
engine 1.2.1 Fix engine leaking oil
engine 1.2.2 Fix engine overheat
engine 1.2.3 Fix occasional engine stalling
engine 2.0.0 Introducing nuclear reactor
You follow the above 3 criteria and correctly decided that your new library hybrid-engine would use a setup.py to declare its dependency engine>=1.2.0,<2, and then your separated application reliable-car would use requirements.txt to declare its dependency engine>=1.2.3,<2 (or you may want to just pin engine==1.2.3). As you see, your choice for their lower bound number are still subtly different, and neither of them uses the latest engine==2.0.0. And here is why.
hybrid-engine depends on engine>=1.2.0 because, the needed add_fuel() API was first introduced in engine 1.2.0, and that capability is the necessity of hybrid-engine, regardless of whether there might be some (minor) bugs inside such version and been fixed in subsequent versions 1.2.1, 1.2.2 and 1.2.3.
reliable-car depends on engine>=1.2.3 because that is the earliest version WITHOUT known issues, so far. Sure there are new capabilities in later versions, i.e. "nuclear reactor" introduced in engine 2.0.0, but they are not necessarily desirable for project reliable-car. (Your yet another new project time-machine would likely use engine>=2.0.0, but that is a different topic, though.)
TL;DR
requirements.txt lists concrete dependencies
setup.py lists abstract dependencies
A common misunderstanding with respect to dependency management in Python is whether you need to use a requirements.txt or setup.py file in order to handle dependencies.
The chances are you may have to use both in order to ensure that dependencies are handled appropriately in your Python project.
The requirements.txt file is supposed to list the concrete dependencies. In other words, it should list pinned dependencies (using the == specifier). This file will then be used in order to create a working virtual environment that will have all the dependencies installed, with the specified versions.
On the other hand, the setup.py file should list the abstract dependencies. This means that it should list the minimal dependencies for running the project. Apart from dependency management though, this file also serves the package distribution (say on PyPI).
For a more comprehensive read, you can read the article requirements.txt vs setup.py in Python on TDS.
Now going forward and as of PEP-517 and PEP-518, you may have to use a pyproject.toml in order to specify that you want to use setuptools as the build-tool and an additional setup.cfg file to specify the details.
For more details you can read the article setup.py vs setup.cfg in Python.
Related
I am developing a python package managed by poetry. The package has some complex requirements that are very difficult to install successfully on my system. I want the ability to install this in editable mode, with the ability to ignore dependencies (something which the developer of poetry frowns on). Unfortunately, I do not have the option of converting this package to a more mature packaging system.
Apparently the simple solution is to create a setup.py for the project and pip install -e that. Since unfortunately poetry has spread like a cancer to many projects now, I will have to employ such a workaround frequently. As such, I want to minimize the tedium by not copying over fields like description which are irrelevant to the developing the package.
What is the minimal setup.py file that I can use as a template for such poetry projects? I assume it must at least include the package name, version and location. Is there anything else?
I am also planning to not put any requirements in the setup.py file, since the whole point is to bypass the requirements defined by poetry and pyproject.toml. I am fine with manually resolving ModuleNotFoundError: No module named 'foo' errors by typing pip install foo.
It appears sufficient to create the following file:
from distutils.core import setup
setup(
name="<PACKAGE_NAME>",
version="<PACKAGE_VERSION>"
)
And also comment out the entire [build-system] block in the pyproject.toml file (see also How do I configure git to ignore some files locally? so you don't accidentally commit to that).
I think the package name and version can be automatically pulled from the toml file as well, but not sure right now how to do it.
When I use the command python setup.py test, all of the documentation I've seen says setuptools will handle installing the testing dependencies. Where does it install them and are they deleted from the machine after the test suite runs? I've noticed none of the testing modules are actually installed into my virtual environment after this command completes.
I understand it takes all of the modules in the tests_require list and installs them somewhere but I'm not sure where, what it does with them afterward and why it does this. Also, is there any way to pass arguments to the command without using flags, like with a config file or something?
Avoid python setup.py test and tests_require, it's crufty and is now deprecated.
That old feature just downloads the test deps to the project's setup directory, which is seldom what the developer wanted or expected to happen! That doesn't work well in a modern CI workflows with virtual environments, where you would want your dependencies installed to site-packages.
The recommended way to do it using setuptools these days is with an extras_require tag.. See here for an example.
It installs them into an automatically-created subdirectory of the code base named .eggs as .eggs. That's because .eggs are designed to be importable from any location.
This will thus most likely not work in a modern environment because packages are not distributed as .eggs (which lost competition to .whls) so setuptools will have to build them from source (with bdist_egg). Which is likely to fail for many widely-used binary packages with nontrivial build requirements (not to mention the time needed and the fact that packages are not tested as .eggs, either, and may fail when packaged like this).
Instead, listing build requirements in requirements.txt and invoking pip install -r requirements.txt before the build seems to have become widespread practice. This does not make setup.py automatically buildable from source by pip though.
I tried to install them myself from setup.py but this proved to be fragile (e.g. if the user doesn't have write access to site-packages).
The best solution adopted by at least a number of high-profile projects seems to be to just make setup.py fail if they are not present. This is especially useful if the requirements are not Python but C libraries as setup.py doesn't know how to install these in the specific environment anyway. As you can see, this complements requirements.txt naturally.
I have an internal utility library that is used by many projects. There is quite a bit of overlap between the projects in the code they pull from the utility library, but as the library grows, so does the amount of extra stuff any individual project gets that it won't be using. This wouldn't be an issue if the library consisted of only python, but the library also bundles in binaries.
Example-
psycopg2 is used in a handful of places within the utility library, but not all projects need db access. Because the development environment isn't the same as the production environment, the utility library also includes psycopg2 binaries for the prod environment.
This grows with openssl libraries, pandas, numpy, scipy, pyarrow, etc. The result is that a small, 50 line, single purpose script that may need db access is bundled into a 100mb+ deployment package.
So what I'd like to do is carve up the utility library into pieces where the projects down stream can choose which pieces to pull in, but keep the utility library code in one easy-to-manage place. That way, this small single purpose application can choose to import internal-util#core, internal-util#db and not include internal-util#numpy and internal-util#openssl
Is what i'm describing possible to do?
Not directly, to my best knowledge. pip installs a package fully, or not at all.
However, if you're careful in your package about how you import things that may require psycopg2 or someotherlargebinarything, you could use the extras_require feature and thus have the package's users choose which dependencies they want to pull in:
setup(
# ...
name='myawesometoolbelt',
extras_require={
'db': ['psycopg2'],
'math': ['numpy'],
},
)
and then, in your requirements.txt, or pip invocation,
myawesometoolbelt[db,math]
Have you tried looking at pip freeze > requirements.txt and pip install -r requirements.txt?
Once you generated your pip list via pip freeze, it is possible to edit which packages you want installed and which to omit from the requirements.txt generated.
You can then pip install -r requirements.txt the things you want back in.
Are there conventions for storing multiple requirements.txt files in a Python code repository. For example, one file for simply running the program, another for day-to-day development, another for making a Windows build.
Some repositories contain two files, requirements.txt and requirements_dev.txt, or requirements.txt and requirements_win.txt - this seems pretty ad-hoc.
I have others with a requires subfolder. But I'm not sure what the meaning of requires/requirements.txt is in this context -- running the application, or for development?
There is no mention of storing multiple requirements files in Structuring your project (Hitchhiker's guide to Python) or pip install (pip documentation).
As far as I am aware, there are no hard-and-fast rules here. At least not via PEP (but someone feel free to correct me).
The Hitchhiker's Guide to Python recommends putting the pip requirements file at the root of your project.
There does not appear to be any requirement that a pip requirements file has to be called requirements.txt. The pip install documentation even uses the example of pip install -r example-requirements.txt.
I would think that the conventions vary from project-to-project and largely depend on your deployment process and project-specific documentation.
I was reading the docs and couldn't wrap my head around it:
Constraints files are requirements files that only control which
version of a requirement is installed, not whether it is installed or
not. Their syntax and contents is nearly identical to Requirements
Files.
There is one key difference: Including a package in a constraints file
does not trigger installation of the package.
So does that mean I need to requirement files first then run constraint?
Need to have both requirements.txt and constraints.txt?
Or just -c requirements.txt?
Could someone please explain in plain English that what the new PIP feature: Constraints Files does?
Update: pip 20.3, released Nov 30, 2020, introduced a new resolver that fixes some design issues. It also reimplements the constraints feature. It is now difficult or impossible to use the feature the way I describe below. I do not understand the new constraints implementation, and I no longer use it. I've had success with pip-compile from pip-tools. I specify top-level requirements in requirements.in, and pip-compile generates a requirements.txt with specific versions an package hashes. See requirements.in and requirements.txt in the ichnaea project for a working example.
Original answer below, for pip 20.2 and previous
I think a constraints file is a good way to keep your "true" requirements separate from your full install list.
It's good practice to fully specify package versions in your requirements file. For example, if you are installing django-allauth with Django LTS, pin it to the latest releases (as of my answer):
Django==1.8.12
django-allauth==0.25.2
When you install the package, it ends up installing some required packages as well. So, you add those as well, so that everyone gets the same versions of packages:
Django==1.8.12
django-allauth==0.25.2
oauthlib==1.0.3
python-openid==2.2.5
requests==2.9.1
requests-oauthlib==0.6.1
And then you get the bug report "Doesn't work under Python 3". Oops, python-openid is Python 2 only, and python3-openid is used instead, further requiring defusedxml:
Django==1.8.12
django-allauth==0.25.2
oauthlib==1.0.3
python-openid==2.2.5 ; python_version < '3.0'
python3-openid==3.0.10 ; python_version >= '3.0'
defusedxml==0.4.1 ; python_version >= '3.0'
requests==2.9.1
requests-oauthlib==0.6.1
Now requirements.txt is getting ugly, and it's hard to see the "requirements" of Django and django-allauth in the mess.
Here is a requirements.txt that refers to a constraints file:
-c constraints.txt
Django==1.8.12
django-allauth==0.25.2
And constraints.txt with a helpful comment:
# django-allauth requirements
oauthlib==1.0.3
python-openid==2.2.5
python3-openid==3.0.10
defusedxml==0.4.1
requests==2.9.1
requests-oauthlib==0.6.1
No Python classifiers are needed, because constraints are only installed if a package requires them, and are ignored otherwise. Additionally, if a package stops requiring another package 2 years down the road, fresh installs will stop installing it.
I think this, plus some comments, is a useful way to communicate what packages you are using for the project, and which ones are included because they are dependencies.
I think it gets even more useful if you are using pip 8.x's hash-checking mode, which requires specifying versions for dependencies-of-dependencies. If you go down that path, I recommend hashin to help you manage the hashes. See browsercompat for a complicated requirements setup using constraints and hashes.
From the book "Secret Recipes of the Python Ninja"
Constraints files differ from requirements files in one key way: putting a package in the constraints file does not cause the package to be installed, whereas a requirements file will install all packages listed. Constraints files are simply requirements files that control which version of a package will be installed but provide no control over the actual installation.
Let say you have requirements.txt file with following code
# requirements.txt
pandas
and constraints.txt
# constraints.txt
# math / science / graph stuff
bokeh==0.11.1
numpy==1.10.4
pandas==0.17.1
scipy==0.17.0
openpyxl==2.3.3
patsy==0.4.1
matplotlib==1.5.1
ggplot==0.6.8
seaborn==0.7.0
scikit-learn==0.17
executing
pip install -c constraints.txt
will install all packages from requirements.txt and using constraints.txt file for version constraint.
Constraint files are very useful when you provide production environments with optimized package compilations for the productive infrastructure.
We provide such environments in docker containers with versions of numpy, scipy, tensorflow, opencv, ... optimized for our production servers. In order to ensure that the requirements files developers set up to make the environment reproducible for them don't overwrite these optimized installations, we use constraint files. They are written as part of the build process. pip is made aware of the constraints by setting the PIP_CONSTRAINT environment variable.
Before, developers always had to make sure their requirements line up with what's available in the prod containers, which can be a pain given that some minor version numbers iterate quite quickly.
I haven't used constrains files myself, so I may be wrong, but here's how I understand it from the documentation.
Let's say, you have multiple projects which you install using pip. Some of them depend on a popular package foobar directly, some indirectly (via their dependencies), some don't depend on it at all.
One day you decide to change foobar code a bit, to solve some problem related to your environment, so you go ahead and create a local copy of foobar. Now you want to ensure that all your projects use this local copy, but you don't want to spend time figuring out which of them depend on foobar and then editing their requirements.txt or setup.py files.
Here comes constraints file, where you point out to your local copy of foobar and use it for all your projects, not caring which of them need foobar, because constrains file only applies when the project being installed actually depends on foobar (whether directly or indirectly).
There's an even better example of possible usage on reddit.