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install packages and run Python with them

Project description

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pip-run provides on-demand temporary package installation for a single interpreter run.

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

  • 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.
  • Leaves no trace of its invocation (except files in pip’s cache).
  • 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:

  • trials and experiments
  • 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.

[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. Any environment variables honored by pip are also honored.

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.

Module Script Runner

Perhaps the most powerful usage of pip-run is its ability to invoke executable modules and packages via runpy (aka python -m):

$ pip-run -q pycowsay -- -m pycowsay "moove over, pip-run"

  -------------------
< moove over, pip-run >
  -------------------
   \   ^__^
    \  (oo)\_______
       (__)\       )\/\
           ||----w |
           ||     ||
cowsay example animation

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 ...

Experiments and Testing

Because pip-run provides a single-command invocation, it is great for experiments and rapid testing of various package specifications.

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.

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
...

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.

Comparison with pipx

The pipx project is another mature project with similar goals. Both projects expose a project and its dependencies in ephemeral environments. The main difference is pipx primarily exposes Python binaries (console scripts) from those environments whereas pip-run exposes a Python context (including runpy scripts).

Feature pip-run pipx
user-mode operation
invoke console scripts  
invoke runpy modules  
run standalone scripts  
interactive interpreter with deps  
re-use existing environment  
ephemeral environments
persistent environments  
PEP 582 support  
Specify optional dependencies  
Python 2 support  

Comparison with virtualenvwrapper mktmpenv

The mkvirtualenv project attempts to address some of the use-cases that pip-run solves, especially with the mktmpenv command, which destroys the virtualenv after deactivation. The main difference is that pip-run is transient only for the invocation of a single command, while mktmpenv lasts for a session.

Feature pip-run mktmpenv
create temporary package environment
re-usable across python invocations  
portable  
one-line invocation  
multiple interpreters in session  
run standalone scripts  
interactive interpreter with deps
re-use existing environment  
ephemeral environments
persistent environments  

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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