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install packages and run Python with them

Project description

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pip-run provides on-demand dependency resolution, making packages available for the duration of an interpreter session.

It replaces this series of commands (or their Windows equivalent):

$ virtualenv --python pythonX.X --system-site-packages $temp/env
$ $temp/env/bin/pip install pkg1 pkg2 -r reqs.txt
$ $temp/env/bin/python ...
$ rm -rf $temp/env

With this single-line command:

$ pythonX.X -m pip-run pkg1 pkg2 -r reqs.txt -- ...

Features include

  • Allows declaration of dependencies at runtime.
  • Downloads missing dependencies and makes their packages available for import.
  • Installs packages to a special staging location such that they’re not installed after the process exits.
  • Relies on pip to cache downloads of such packages for reuse.
  • Supersedes installed packages when required.
  • Relies on packages already satisfied [1].
  • Re-uses the pip tool chain for package installation.

pip-run is not intended to solve production dependency management, but does aim to address the other, one-off scenarios around dependency management:

  • build setup
  • test runners
  • just in time script running
  • interactive development
  • bug triage

pip-run is a compliment to Pip and Virtualenv and Setuptools, intended to more readily address the on-demand needs and supersede some features like setup_requires.

[1]Except when a requirements file is used.

Installation

pip-run is meant to be installed in the system site packages alongside pip, though it can also be installed in a virtualenv.

Usage

  • as script launcher
  • as runtime dependency context manager
  • as interactive interpreter in dependency context
  • as module launcher (akin to python -m)

Invoke pip-run from the command-line using the console entry script (simply pip-run) or using the module executable ( python -m pip-run). This latter usage is particularly convenient for testing a command across various Python versions.

Parameters following pip-run are passed directly to pip install, so pip-run numpy will install numpy (reporting any work done during the install) and pip-run -q -r requirements.txt will quietly install all the requirements listed in a file called requirements.txt.

Following the parameters to pip install, one may optionally include a -- after which any parameters will be passed to a Python interpreter in the context.

Examples

The examples folder in this project includes some examples demonstrating the power and usefulness of the project. Read the docs on those examples for instructions.

In many of these examples, the option -q is passed to pip-run to suppress the output from pip.

Interactive Interpreter

pip-run also offers a painless way to run a Python interactive interpreter in the context of certain dependencies:

$ /clean-install/python -m pip-run -q boto
>>> import boto
>>>

Command Runner

Note that everything after the – is passed to the python invocation, so it’s possible to have a one-liner that runs under a dependency context:

$ python -m pip-run -q requests -- -c "import requests; print(requests.get('https://pypi.org/project/pip-run').status_code)"
200

As long as pip-run is installed in each of Python environments on the system, this command can be readily repeated on the other python environments by specifying the relevant interpreter:

$ python2.7 -m pip-run ...

or on Windows:

$ py -2.7 -m pip-run ...

Script Runner

Let’s say you have a script that has a one-off purpose. It’s either not part of a library, where dependencies are normally declared, or it is normally executed outside the context of that library. Still, that script probably has dependencies, say on requests. Here’s how you can use pip-run to declare the dependencies and launch the script in a context where those dependencies have been resolved.

First, add a __requires__ directive at the head of the script:

#!/usr/bin/env python

__requires__ = ['requests']

import requests

req = requests.get('https://pypi.org/project/pip-run')
print(req.status_code)

Then, simply invoke that script with pip-run:

$ python -m pip-run -q -- myscript.py
200

The format for requirements must follow PEP 508.

Note that URLs specifiers are not supported by pip, but pip-run supports a global __dependency_links__ attribute which can be used, for example, to install requirement from a project VCS URL:

#!/usr/bin/env python

__requires__ = ['foo==0.42']
__dependency_links__ = ['git+ssh://git@example.com/repo.git#egg=foo-0.42']

[...]

pip-run also recognizes a global __index_url__ attribute. If present, this value will supply --index-url to pip with the attribute value, allowing a script to specify a custom package index:

#!/usr/bin/env python

__requires__ = ['my_private_package']
__index_url__ = 'https://my.private.index/'

import my_private_package
...

Replacing setup_requires

Following the script example, you can make your setup.py file compatible with pip-run by declaring your depenedencies in the __requires__ directive:

#!/usr/bin/env python

__requires__ = ['setuptools', 'setuptools_scm']

import setuptools

setuptools.setup(
    ...
    setup_requires=__requires__,
)

When invoked with pip-run, the dependencies will be assured before the script is run, or if run with setuptools, the dependencies will be loaded using the older technique, so the script is backward compatible.

Replacing tests_require

Although this example is included for completeness, because the technique is somewhat clumsy, the author currently recommends using tox for running tests except in extremely lean environments.

You can also replace tests_require. Consider a package that runs tests using setup.py test and relies on the tests_require directive to resolve dependencies needed during testing. Simply declare your dependencies in a separate file, e.g. “tests/requirements.txt”:

cat > tests/requiremenst.txt
pytest

For compatibility, expose those same requirements as tests_require in setup.py:

with io.open('tests/requirements.txt') as tr:
    tests_require = [
            line.rstrip()
            for line in tr
            if re.match('\w+', line)
    ]

setuptools.setup(
    ...
    tests_require=tests_require,
)

Then invoke tests with pip-run:

$ python -m pip-run -r tests/requirements.txt -- setup.py test

While still supporting the old technique:

$ python setup.py test

Supplying parameters to Pip

If you’ve been using pip-run, you may have defined some requirements in the __requires__ of a script, but now you wish to install those to a more permanent environment. pip-run provides a routine to facilitate this case:

$ python -m pip_run.read-deps script.py my_dependency

If you’re on Unix, you may pipe this result directly to pip:

$ pip install $(python -m pip_run.read-deps script.py)

And since pipenv uses the same syntax, the same technique works for pipenv:

$ pipenv install $(python -m pip_run.read-deps script.py)

How Does It Work

pip-run effectively does the following:

  • pip install -t $TMPDIR
  • PYTHONPATH=$TMPDIR python
  • cleanup

For specifics, see pip_run.run().

Limitations

  • Due to limitations with pip, pip-run cannot run with “editable” (-e) requirements.
  • pip-run uses a sitecustomize module to ensure that .pth files in the requirements are installed. As a result, any environment that has a sitecustomize module will find that module masked when running under pip-run.

Integration

The author created this package with the intention of demonstrating the capability before integrating it directly with pip in a command such as pip run. After proposing the change, the idea was largely rejected in pip 3971.

If you would like to see this functionality made available in pip, please upvote or comment in that ticket.

Versioning

pip-run uses semver, so you can use this library with confidence about the stability of the interface, even during periods of great flux.

Testing

Invoke tests with tox.

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