Project Status

PyOxidizer is functional and works for many use cases. However, there are still a number of rough edges, missing features, and known limitations. Please file issues at!

What’s Working

The basic functionality of creating binaries that embed a self-contained Python works on Linux, Windows, and macOS. The general approach should work for other operating systems.

TOML configuration files allow extensive customization of packaging and run time behavior. Many projects can be successfully packaged with PyOxidizer today.

Major Missing Features

An Official Build Environment

Compiling binaries that work on nearly every target system is hard. On Linux, things like glibc symbol versions from the build machine can leak into the built binary, effectively requiring a new Linux distribution to run a binary.

In order to make the binary build process robust, we will need to provide an execution environment for binaries. On Linux, this likely entails making something like a Docker image available. On Windows and macOS, we might have to provide a tarball. In all cases, we want this environment to be integrated into pyoxidizer build so end users don’t have to worry about jumping through hoops to build portable binaries.

C Extensions

Building and using compiled extension modules (e.g. C extensions) is not yet supported. This is a hard problem on a few dimensions. We have a plan to solve it, however.

In some cases, C extensions may just work. But it isn’t very well tested.

Incomplete pyoxidizer Commands

pyoxidizer add and pyoxidizer analyze aren’t fully implemented.

There is no pyoxidizer upgrade command.

Work on all of these is planned.

More Robust Packaging Support

Currently, we produce an executable via Cargo. Often a self-contained executable is not suitable. We may have to run some Python modules from the filesystem because of limitations in those modules. In addition, some may wish to install custom files alongside the executable.

We want to add a myriad of features around packaging functionality to facilitate these things. This includes:

  • Copying arbitrary files to live next to the executable.
  • Specifying that certain modules should not be embedded in the binary.
  • Support for __file__.
  • A pyoxidizer command for turnkey building and assembling of all files.
  • A build mode that produces an instrumented binary, runs it a few times to dump loaded modules into files, then builds it again with a pruned set of resources.

Making Distribution Easy

We don’t yet have a good story for the distributing part of the application distribution problem. We’re good at producing executables. But we’d like to go the extra mile and make it easier for people to produce installers, .dmg files, tarballs, etc.

This includes providing build environments for e.g. non-MUSL based Linux executables.

It also includes support for auditing for license compatibility (e.g. screening for GPL components in proprietary applications) and assembling required license texts to satisfy notification requirements in those licenses.

Partial Terminfo and Readline Support

The readline and curses support for the standalone Python distributions is currently not great.

First, the non-GPL libedit version of the Python readline extension may not work on Linux. So if you want a non-GPL binary that uses the readline extension, you may be out of luck until this is fixed.

The bigger issue is with terminal database support. The ncurses library needs to know how to load a terminfo database so it knows which features a terminal supports. Without this database, terminal interaction can be wrong or unexpected. For example, pressing the backspace key could advance the cursor instead of removing the previous character!

Typically the path to the database is specified at build time. The ncurses library is never distributed across machines, so this is typically fine. Linux distributions put the terminfo database in different locations, so hard-coding a fixed location at compile time is the wrong approach for PyOxidizer.

It is possible to compile and embed a database into the ncurses library. But it is impossible to embed the entire database because of compilation errors in ncurses. And the database could bloat the size of the binary. If we only included some database entries, we would be playing gatekeeper and may exclude some terminal definitions that people need.

ncurses does support specifying the location to the database via environment variables (notably TERMINFO and TERMINFO_DIRS). One possible approach is to sniff for the location of the database at known popular locations at run-time. We could potentially make this lazy so it only occurs if Python extensions using ncurses are loaded. We could also make it easy to distribute a database next to built application and tell built binaries to load it relative to the binary.

There are definitely options here. But for now, the lack of a terminfo / termcap database in the embedded Python distribution can make Python interact with terminals in unexpected ways.

Test Coverage

The test coverage for PyOxidizer is pretty bad. We need to write a lot of tests.

Lesser Missing Features

Python Version Support

Only Python 3.7 is currently supported. Support for older Python 3 releases is possible. But the project author hopes we only need to target the latest/greatest Python release.

Reordering Resource Files

There is not yet support for reordering .py and .pyc files in the binary. This feature would facilitate linear read access, which could lead to faster execution.

Compressed Resource Files

Binary resources are currently stored as raw data. They could be stored compressed to keep binary size in check (at the cost of run-time memory usage and CPU overhead).

Nightly Rust Required on Windows

Windows currently requires a Nightly Rust to build (you can set the environment variable RUSTC_BOOTSTRAP=1 to work around this) because the static-nobundle library type is required. tracks making this feature stable. It might be possible to work around this by adding an __imp_ prefixed symbol in the right place or by producing a empty import library to satisfy requirements of the static linkage kind. See for more.

Cross Compiling

Cross compiling is not yet supported. We hope to and believe we can support this someday. We would like to eventually get to a state where you can e.g. produce Windows and macOS executables from Linux. It’s possible.

TOML Configuration File

Naming and semantics in the TOML configuration files can be significantly improved. There’s also various missing packaging functionality.

Poor Rust Error Handling

Error handling in build-time Rust code isn’t great. Expect to see the pyoxidizer executable to crash from time to time. The code that runs in binaries built with PyOxidizer is held to a higher standard. Crashes should not occur and will be treated as serious bugs!

Eventual Features

The immediate goal of PyOxidizer is to solve packaging and distribution problems for Python applications. But we want PyOxidizer to be more than just a packaging tool: we want to add additional features to PyOxidizer to bring extra value to the tool and to demonstrate and/or experiment with alternate ways of solving various problems that Python applications frequently encounter.

Lazy Module Loading

When a Python module is import``ed, its code is evaluated. When applications consist of dozens or even hundreds of modules, the overhead of executing all this code at ``import time can be substantial and add up to dozens of milliseconds of overhead - all before your application runs a meaningful line of code.

We would like PyOxidizer to provide lazy module importing so Python’s import machinery can defer evaluating a module’s code until it is actually needed. With features in modern versions of Python 3, this feature could likely be enabled by default. And since many PyOxidizer applications are frozen and have total knowledge of all import``able modules at build time, ``PyOxidizer could return a lazy module object after performing a simple Rust HashMap lookup. This would be extremely fast.

Alternate Module Serialization Techniques

Related to lazy module loading, there is also the potential to explore alternate module serialization techniques. Currently, the way PyOxidizer and .pyc files work is that a Python code object is serialized with the marshal module. At module load time, the code object is deserialized and then executed. This deserialization plus code execution has overhead.

It is possible to devise alternate serialization and load techniques that don’t rely on marshal and possibly bypass having to run as much code at module load time. For example, one could devise a format for serializing various PyObject types and then adjusting pointers inside the structs at run time. This is kind of a crazy idea. But it could work.

Module Order Tracing

Currently, resource data is serialized on disk in alphabetical order according to the resource name. e.g. the bar module is serialized before the foo module.

We would like to explore a mechanism to record the order in which modules are loaded as part of application execution and then reorder the serialized modules such that they are stored in load order. This will facilitate linear reads at application run time and possibly provide some performance wins (especially on devices with slow I/O).

Module Import Performance Tracing

PyOxidizer has near total visibility into what Python’s module importer is doing. It could be very useful to provide forensic output of what modules import what, how long it takes to import various modules, etc.

CPython does have some support for module importing tracing. We think we can go a few steps farther. And we can implement it more easily in Rust than what CPython can do in C. For example, with Rust, one can use the inferno crate to emit flame graphs directly from Rust, without having to use external tools.

Built-in Profiler

There’s potential to integrate a built-in profiler into PyOxidizer applications. The excellent py-spy sampling profiler (or the core components of it) could potentially be integrated directly into PyOxidizer such that produced applications could self-profile with minimal overhead.

It should also be possible for PyOxidizer to expose mechanisms for Rust to receive callbacks when Python’s profiling and tracing hooks fire. This could allow building a powerful debugger or tracer in Rust.

Command Server

A known problem with Python is its startup overhead. The maintainer of PyOxidizer has raised this issue on Python’s mailing list a few times.

PyOxidizer helps with this problem by eliminating explicit filesystem I/O and allowing modules to be imported faster. But there’s only so much that can be done and startup overhead can still be a problem.

One strategy to combat this problem is the use of persistent command server daemons. Essentially, on the first invocation of a program you spawn a background process running Python. That process listens for command requests on a pipe, socket, etc. You send the current command’s arguments, environment variables, other state, etc to the background process. It uses its Python interpreter to execute the command and send results back to the main process. On the 2nd invocation of your program, the Python process/interpreter is already running and meaningful Python code can be executed immediately, without waiting for the Python interpreter and your application code to initialize.

This approach is used by the Mercurial version control tool, for example, where it can shave dozens of milliseconds off of hg command service times.

PyOxidizer could potentially support command servers as a built-in feature for any Python application.


PyO3 are alternate Rust bindings to Python from rust-cpython, which is what pyembed currently uses.

The PyO3 bindings seem to be ergonomically better than rust-cpython. PyOxidizer may switch to PyO3 someday. A hard blocker is that as of at least June 2019, PyO3 requires Nightly Rust. We do not wish to make Nightly Rust a requirement to run PyOxidizer.