Packaging Python Files

The most important packaged resource type are arguably Python files: source modules, bytecode modules, extension modules, package resources, etc.

For PyOxidizer to recognize these Python resources as Python resources (as opposed to regular files), you will need to use the methods on the PythonExecutable Starlark type to use the settings from the thing being built to scan for resources, possibly performing a Python packaging action (such as invoking pip install) along the way.

This documentation covers the available methods and how they can be used.

PythonExecutable Python Resources Methods

The PythonExecutable Starlark type has the following methods that can be called to perform an action and obtain an iterable of objects representing discovered resources:

Invokes pip download with specified arguments and collects resources discovered from downloaded Python wheels.
Invokes pip install with specified arguments and collects all resources installed by that process.
Recursively scans a filesystem directory for Python resources in a typical Python installation layout.
Invokes python install for a given path and collects resources installed by that process.
Reads Python resources present in an already populated virtualenv.

Typically, the Starlark types resolved by these method calls are passed into a method that adds the resource to a to-be-generated entity, such as the PythonExecutable Starlark type.

The following sections demonstrate common use cases.

Packaging an Application from a PyPI Package

In this section, we’ll show how to package the pyflakes program using a published PyPI package. (Pyflakes is a Python linter.)

First, let’s create an empty project:

$ pyoxidizer init-config-file pyflakes

Next, we need to edit the configuration file to tell PyOxidizer about pyflakes. Open the pyflakes/pyoxidizer.bzl file in your favorite editor.

Find the make_exe() function. This function returns a PythonExecutable instance which defines a standalone executable containing Python. This function is a registered target, which is a named entity that can be individually built or run. By returning a PythonExecutable instance, this function/target is saying build an executable containing Python.

The PythonExecutable type holds all state needed to package and run a Python interpreter. This includes low-level interpreter configuration settings to which Python resources (like source and bytecode modules) are embedded in that executable binary. This type exposes an add_python_resources() method which adds an iterable of objects representing Python resources to the set of embedded resources.

Elsewhere in this function, the dist variable holds an instance of PythonDistribution. This type represents a Python distribution, which is a fancy way of saying an implementation of Python.

Two of the methods exposed by PythonExecutable are pip_download() and pip_install(), which invoke pip commands with settings to target the built executable.

To add a new Python package to our executable, we call one of these methods then add t he results to our PythonExecutable instance. This is done like so:

# or

When called, these methods will effectively run pip download pyflakes==2.2.0 or pip install pyflakes==2.2.0, respectively. Actions are performed in a temporary directory and after pip runs, PyOxidizer will collect all the downloaded/installed resources (like module sources and bytecode data) and return them as an iterable of Starlark values. The exe.add_python_resources() call will then teach the built executable binary about the existence of these resources. Many resource types will be embedded in the binary and loaded from binary. But some resource types (notably compiled extension modules) may be installed next to the built binary and loaded from the filesystem.

Next, we tell PyOxidizer to run pyflakes when the interpreter is executed:

python_config.run_mode = "eval:from pyflakes.api import main; main()"

This says to effectively run the Python code eval(from pyflakes.api import main; main()) when the embedded interpreter starts.

The new make_exe() function should look something like the following (with comments removed for brevity):

def make_exe():
    dist = default_python_distribution()

    policy = dist.make_python_packaging_policy()
    policy.extension_module_filter = "all"
    policy.include_distribution_sources = True
    policy.include_distribution_resources = True
    policy.include_test = False

    config = dist.make_python_interpreter_config()
    config.run_mode = "eval:from pyflakes.api import main; main()"

    exe = dist.to_python_executable(


    return exe

With the configuration changes made, we can build and run a pyflakes native executable:

# From outside the ``pyflakes`` directory
$ pyoxidizer run --path /path/to/pyflakes/project -- /path/to/python/file/to/analyze

# From inside the ``pyflakes`` directory
$ pyoxidizer run -- /path/to/python/file/to/analyze

# Or if you prefer the Rust native tools
$ cargo run -- /path/to/python/file/to/analyze

By default, pyflakes analyzes Python source code passed to it via stdin.

Packaging an Application from an Existing Virtualenv

This scenario is very similar to the above example. So we’ll only briefly describe what to do so we don’t repeat ourselves.:

$ pyoxidizer init-config-file /path/to/myapp

Now edit the pyoxidizer.bzl so the make_exe() function look like the following:

def make_exe():
    dist = default_python_distribution()

    policy = dist.make_python_packaging_policy()
    policy.extension_module_filter = "all"
    policy.include_distribution_sources = True
    policy.include_distribution_resources = False
    policy.include_test = False

    config = dist.make_python_interpreter_config()
    config.run_mode = "eval:from myapp import main; main()"

    exe = dist.to_python_executable(


    return exe

Of course, you need a populated virtualenv!:

$ python3.8 -m venv /path/to/virtualenv
$ /path/to/virtualenv/bin/pip install -r /path/to/requirements.txt

Once all the pieces are in place, simply run pyoxidizer to build and run the application:

$ pyoxidizer run --path /path/to/myapp


When consuming a pre-populated virtualenv, there may be compatibility differences between the Python distribution used to populate the virtualenv and the Python distributed used by PyOxidizer at build and application run time.

For best results, it is recommended to use a packaging method like pip_install(...) or setup_py_install(...) to use PyOxidizer’s Python distribution to invoke Python’s packaging tools.

Packaging an Application from a Local Python Package

Say you have a Python package/application in a local directory. It follows the typical Python package layout and has a file and Python files in sub-directories corresponding to the package name. e.g.:

You have a number of choices as to how to proceed here. Again, the workflow is very similar to what was explained above. The main difference is the content of the pyoxidizer.bzl file and the exact method to call to obtain the Python resources.

You could use pip install <local path> to use pip to process a local filesystem path:


If the pyoxidizer.bzl file is in the same directory as the directory you want to process, you can derive the absolute path to this directory via the CWD Starlark variable:


If you don’t want to use pip and want to run directly, you can do so:


Or if you don’t want to run a Python packaging tool at all and just scan a directory tree for Python files:

exe.add_python_resources(exe.read_package_root(CWD, ["mypackage"]))


In this mode, all Python resources must already be in place in their final installation layout for things to work correctly. Many files perform additional actions such as compiling Python extension modules, installing additional files, dynamically generating some files, or changing the final installation layout.

For best results, use a packaging method that invokes a Python packaging tool (like pip_install(...) or setup_py_install(...).

Choosing Which Packaging Method to Call

There are a handful of different methods for obtaining Python resources that can be added to a resource collection. Which one should you use?

The reason there are so many methods is because the answer is: it depends.

Each method for obtaining resources has its niche use cases. That being said, the preferred method for obtaining Python resources is pip_download(). However, pip_download() may not work in all cases, which is why other methods exist.

PythonExecutable.pip_download() runs pip download and attempts to fetch Python wheels for specified packages, requirements files, etc. It then extracts files from inside the wheel and converts them to Python resources which can be added to resource collectors.


pip_download() will only work if a compatible Python wheel package (.whl file) is available. If the configured Python package repository doesn’t offer a compatible wheel for the specified package or any of its dependencies, the operation will fail.

Many Python packages do not yet publish wheels (only .tar.gz archives) or don’t publish at all to Python package repositories (this is common in corporate environments, where you don’t want to publish your proprietary packages on PyPI or you don’t run a Python package server).


Not all build targets support pip_download() for all published packages. For example, when targeting Linux musl libc, built binaries are fully static and aren’t capable of loading Python extension modules (which are shared libraries). So pip_download() only supports source-only Python wheels in this configuration.

Another advantage of pip_download() is it supports cross-compiling. Unlike pip install, pip download supports arguments that tell it which Python version, platform, implementation, etc to download packages for. PyOxidizer automatically tells pip download to download wheels that are compatible with the target environment you are building for. This means you can do things like download wheels containing Windows binaries when building on Linux.


Cross-compiling is not yet fully supported by PyOxidizer and likely doesn’t work in many cases. However, this is a planned feature (at least for some configurations) and pip_download() is likely the most future-proof mechanism to support installing Python packages when cross-compiling.

A potential downside with pip_download() is that it only supports classical Python binary loading/shipping techniques. If you are trying to produce a statically linked executable containing custom Python extension modules, pip_download() won’t work for you.

After pip_download, PythonExecutable.pip_install() and PythonExecutable.setup_py_install() are the next most-preferred packaging methods.

Both of these work by locally running a Python packaging action (pip install or python install, respectively) and then collecting resources installed by that action.

The advantage over pip download is that a pre-built Python wheel does not have to be available and published on a Python package repository for these commands to work: you can run either against say a local version control checkout of a Python project and it should work.

The main disadvantage over pip download is that you are running Python packaging operations on the local machine as part of building an executable. If your package contains just Python code, this should just work. But if you need to compile extension modules, there’s a good chance your local machine may either not be able to build them properly or will build those extension modules in such a way that they aren’t compatible with other machines you want to run them on.

The final options for obtaining Python resources are PythonExecutable.read_package_root() and PythonExecutable.read_virtualenv(). Both of these methods rely on traversing a filesystem tree that is already populated with Python resources. This should just work if only pure Python resources are in play. But if there are compiled Python extension modules, all bets are off and there is no guarantee that found extension modules will be compatible with PyOxidizer or will have binary compatibility with other machines. These resource discovery mechanisms also rely on state not under the control of PyOxidizer and therefore packaging results may be highly inconsistent and not reproducible across runs. For these reasons, read_package_root() and read_virtualenv() are the least preferred methods for Python resource discovery.