librt

library0.15.0pypypi✓ verified 25d ago

librt is the Mypyc runtime library, providing efficient C implementations of various Python standard library classes and functions. Mypyc leverages this library to produce faster C extensions when compiling Python code. It is primarily an internal dependency for `mypyc` and `mypy` (since version 1.19.0 for fixed-format cache serialization). The current version is 0.8.1, with development occurring in the main `mypy` repository and releases synced to the `librt` PyPI package.

testing

pip install librt

github ↗package ↗

INSTALL

IMPORT

SIG · LIBRT

librt

testingpythonv0.15.0

Install

1.9s avg

Import

—

Disk

17MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v0.15.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.000s · 19.1MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.9s · import 0.000s · 20MB

17MB installed

● package 17MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

librt

✓ This library is primarily an internal runtime dependency for mypyc-compiled code and recent versions of mypy. Direct import of its internal symbols by end-user applications is generally not intended.

librt provides C implementations used by mypyc-generated extensions. While Python might theoretically allow importing internal parts (e.g., `librt.internal`), this is not part of its public API and can lead to unexpected issues or breaking changes. For example, `mypy` itself uses `librt` for cache serialization and deserialization, often through internal mechanisms rather than direct `import librt` in user code.

librt is a runtime library for code compiled with `mypyc`. Therefore, its 'quickstart' involves demonstrating how to use `mypyc` to compile Python code. The compiled code will then depend on `librt` at runtime. The example shows a simple Python function that `mypyc` could compile, implicitly leveraging `librt`'s optimizations.

# librt is implicitly used by mypyc-compiled modules. # A typical quickstart involves using mypyc, which then utilizes librt. # First, ensure librt (and mypy, which includes mypyc) are installed. # pip install mypy mypyc # example_module.py # This module will be compiled by mypyc, which relies on librt at runtime. def factorial(n: int) -> int: result = 1 for i in range(1, n + 1): result *= i return result if __name__ == '__main__': # In a real scenario, this would be compiled and imported as a C extension. # For illustration, let's just run it as normal Python. # To compile: mypyc example_module.py # This creates a C extension (e.g., example_module.cpython-XYZ.so) that depends on librt. print(f'Factorial of 5: {factorial(5)}')

Debug

Known issues

breakinglibrt does not officially support PyPy. If your project targets PyPy and has `librt` as a dependency (e.g., through `mypy` for type checking), you may need to skip it in your CI matrix for PyPy environments.

fix

Avoid using librt-dependent components in PyPy environments or configure CI to exclude librt-related checks/builds for PyPy.

affects: All versions

gotchalibrt's Application Binary Interface (ABI) is not explicitly versioned, and changes to it can lead to compatibility issues with `mypyc`-compiled extensions. This can cause breakage if `librt` is updated independently of `mypyc` or the compiled application.

fix

Ensure `librt` is kept in sync with the `mypyc` version used for compilation. Pinning exact versions of `librt` and `mypyc` is recommended, especially in production environments or when distributing `mypyc`-compiled code.

affects: All versions

gotchalibrt is primarily an internal runtime component. Direct imports or reliance on its internal API in user-facing Python code are discouraged, as these interfaces are subject to change without standard deprecation warnings.

fix

Treat librt as an implementation detail of mypyc. Do not directly import or use symbols from `librt` in your application code; instead, rely on the behavior of `mypyc`-compiled modules.

affects: All versions

deprecatedMypy 1.19.0 introduced `librt` as a dependency for its fixed-format cache serialization. Older versions of `mypy` (before 1.19.0) did not require `librt` for this purpose, relying instead on JSON-based caching.

fix

If upgrading `mypy` to 1.19.0 or newer, ensure `librt` is installed alongside it. For older `mypy` versions, `librt` is not required for cache functionality.

affects: <1.19.0 (mypy)

Upgrade

Version history

0.15.0latest on PyPI · released Aug 7, 2026

Audit

Dependencies

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Agent activity

12 hits · last 30 days

node

Resources

githubhttps://github.com/mypyc/librt ↗

packagehttps://pypi.org/project/librt/ ↗