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Description:

prequ 1.4.7

Tools for Python requirement handling. Helps in keeping your
requirements files complete and up-to-date.

Note: Prequ is currently designed to work with a virtual env, so
compatibility with non-virtual Python environments are not guaranteed to
work at the moment.

Background
Every non-library Python project should have a requirements.txt file
which lists required Python packages for the project, i.e. its
dependencies. It would be easy to just list the dependencies with their
minimum and maximum versions in there, but that’s not a good practice.
If versions of the dependencies are not pinned to exact versions, it’s
uncertain which version of the packages get installed. Even pinning the
direct dependencies is not enough, since project dependencies might have
their own dependencies (project’s indirect dependencies) and those
should be pinned too. That’s where Prequ comes in: it makes it easy to
generate the list of those pinned direct and indirect dependencies from
the non-pinned requirements.
There is also a good article by Vincent Driessen which explains it more
thoroughly why you should pin your packages.
Prequ is a fork of pip-tools by Vincent Driessen. Pip-tools was a fine
project, but I wanted to add couple new features and make some changes
to existing workflows. There were also couple bugs that I needed to be
fixed sooner than later. Most of those bugs were already fixed in
GitHub pull requests, but weren’t merged to pip-tools. That’s why I
decided to create my own fork.

Installation
$ pip install prequ

Example usage for prequ update
Suppose you have a Flask project, and want to pin it for production.
You need to specify a configuration file for Prequ. The configuration
file minimally defines so-called source requirements, i.e. list of
Python packages (with optional version specifiers). This can be done by
writing following section to setup.cfg:
[prequ]
requirements = Flask
Now, run prequ update:
$ prequ update
*** Compiling requirements.txt
And it will produce your requirements.txt, with all the Flask
dependencies and all underlying dependencies pinned. Put this file
under version control as well. Generated file will look like this:
# This file is autogenerated by Prequ. To update, run:
#
# prequ update
#
flask==0.10.1
itsdangerous==0.24
jinja2==2.7.3
markupsafe==0.23
werkzeug==0.10.4
To add/remove packages, add/remove them to/from setup.cfg and
re-run prequ update. To upgrade all packages, remove the generated
requirements.txt and run prequ update again.

Example usage for prequ sync
Now that you have a requirements.txt, you can use prequ sync
to update your virtual env to reflect exactly what’s in there. Note:
this will install/upgrade/uninstall everything necessary to match the
requirements.txt contents.
$ prequ sync
Uninstalling flake8-2.4.1:
Successfully uninstalled flake8-2.4.1
Collecting click==4.1
Downloading click-4.1-py2.py3-none-any.whl (62kB)
...
Found existing installation: click 4.0
Uninstalling click-4.0:
Successfully uninstalled click-4.0
Successfully installed click-4.1
To sync multiple *.txt dependency lists, just pass them in via
command line arguments e.g.:
$ prequ sync requirements.txt requirements-dev.txt
Passing in empty arguments would cause it to default to
requirements.txt.

More detailed example of Prequ configuration
Prequ supports defining couple options for the requirement compiling and
automatically building wheels from pip URLs. Here is a more detailed
example of a Prequ configuration to demonstrate those features:
[prequ]
annotate = yes
generate_hashes = no
header = yes
extra_index_urls =
https://shuup.github.io/pypi/simple/
wheel_dir = wheels
wheel_sources =
github_shuup = git+ssh://git@github.com/shuup/{pkg}@v{ver}

requirements =
django~=1.9.5
shuup~=0.5.0
shuup-stripe==0.4.2 (wheel from github_shuup)

requirements-dev =
flake8
pep8-naming
Now running prequ update will first build a wheel package for
shuup-stripe and then it will generate two files, requirements.txt
and requirements-dev.txt:
$ prequ update
*** Building wheel for shuup-stripe 0.4.2 from
git+ssh://git@github.com/shuup/shuup-stripe@v0.4.2
Collecting git+ssh://git@github.com/shuup/shuup-stripe@v0.4.2
...
Successfully built shuup-stripe
Cleaning up...
Removing source in /tmp/pip-b5rf3ioq-build
*** Built: wheels/shuup_stripe-0.4.2-py2.py3-none-any.whl
*** Compiling requirements.txt
*** Compiling requirements-dev.txt
The generated files will have extra-index-url option as specified and
and find-links for the wheels directory:
$ cat requirements.txt
# This file is autogenerated by Prequ. To update, run:
#
# prequ update
#
--extra-index-url https://shuup.github.io/pypi/simple/
--find-links wheels

Babel==2.3.4 # via shuup
django-bootstrap3==6.2.2 # via shuup
...
$ cat requirements-dev.txt
# This file is autogenerated by Prequ. To update, run:
#
# prequ update
#
--extra-index-url https://shuup.github.io/pypi/simple/
--find-links wheels

flake8==3.3.0
mccabe==0.6.1 # via flake8
pep8-naming==0.4.1
pycodestyle==2.3.1 # via flake8
pyflakes==1.5.0 # via flake8