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Run commands using Python virtual environment

Project description

Doing this…

venv-run myapp.py

…is more convenient than this…

source myvenv/bin/activate
python myapp.py
deactivate

That is the main motivation of this tool!

venv-run is a tool for running commands with a Python virtual environment without explicitly activating it (and deactivating it when you are done). Essentially it runs your command with the virtual environment’s binary path prepended to the system’s PATH environment variable. Another nice thing about venv-run is that it tries to find the environment’s directory from your current working directory so you can save some typing.

Installation

Using pip

pip install venv-run

From source

If you have pip available in your system, then the recommended way to install from source is doing:

# From the source root
pip install .

Alternatively, you can call setup.py directly, but remember that it does not provide an “uninstall” command (this form is useful for OS distribution packagers):

python setup.py install

Usage

venv-run can be called directly as a shell command:

venv-run [OPTIONS] [--] [CMD]

When called, the first thing venv-run does is to look for a (single) virtual environment under your current working directory. After it encounters the environment’s directory, it runs your command with the environment’s binary path prepended to the system’s binary path.

All the examples in this section assume you have a virtual environment created in the working directory.

Running a Python script

Suppose you have a Python project in my-python-project and have created a virtual environment like the example below:

$ cd my-python-project
$ python -m venv myvenv

You can call a Python script of your project using that environment with the command:

$ venv-run myapp.py

If myapp.py accepts arguments, you can pass them normally:

$ venv-run myapp.py --foo --bar baz

Calling Python

The virtual environment’s Python interpreter is implicitly called in the following situations:

  • When no command is passed to venv-run;

  • When the first word of CMD is not an executable and either starts with - or ends with .py. In this case, python is prepended to CMD (the example in the previous section falls under this condition).

Thus, for example, you can start an interactive session with the environment’s Python by simply calling:

$ venv-run

And you can call a module installed in the environment with:

$ venv -m path.to.module

For both cases, it’s also okay to explicitly call the interpreter (e.g. venv-run python -m path.to.module).

Calling executables

If you want to call an executable installed in your virtual environment, you can call it like in the example below:

# Suppose I'm using flask to develop a Web application and want to start
# the development server
$ venv-run flask run

The executable does not need to be really installed in the environment. The next example starts the system’s bash with venv/bin prepended to PATH:

$ venv-run bash

Locally installing and using a Python package

Let’s say you want to use bpython to interactively use and test your project’s modules.

You can install it:

$ venv-run pip install bpython

And the run it at will:

$ venv-run bpython

Multiple virtual environments

venv-run refuses to continue if it finds more than one virtual environment. You can pass --venv PATH_TO_VENV to point the environment to be used for such cases.

Options ambiguity

If CMD uses options conflicting with venv-run’s own options, then you can prepend CMD with -- to mark the beginning of CMD. Example:

$ venv-run python -h # Shows venv-run's help message
$ venv-run -- python -h # Shows python's help message

Use cases

With pre-commit

A common specific use case is to be able to run pre-commit system and script hooks written in Python so that they’re run within the virtual environment of the project, even if it hadn’t been activated beforehand. This may happen for example when pre-commit is launched when committing from an IDE that is not virtualenv self-aware, initially launched in an environment different from the project’s virtual one.

Another one is to get tools that need to be run in the project’s virtual environment to work properly – such as mypy, pylint, and pytype to name a few – to actually run in it. To do this, instead of using the usual project provided hooks, install the respective tool package along with its dependencies and plugins in the project’s virtual environment and use a local pre-commit hook like:

- repo: local
  hooks:
    - id: pylint
      name: pylint
      language: python
      additional_dependencies: [venv-run]
      entry: venv-run pylint
      types: [python]

Be sure to look into the project provided hooks to see if there are any additional needed settings, for example args, anything special in entry, require_serial or the like, and replicate in your local hook as applicable.

Author

Gustavo José de Sousa

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