fastcov

library1.17pypypi✓ verified 85d ago

fastcov is a massively parallel gcov wrapper for generating intermediate coverage formats (like lcov info) quickly. It processes .gcda/.gcno files in parallel using subprocesses and hashes source files to avoid re-processing. Current version is 1.16, requires Python >=3.5, and is maintained on GitHub.

testing devops

pip install fastcov

github ↗package ↗

INSTALL

IMPORT

SIG · FASTCOV

fastcov

testingpythonv1.17

Install

1.5s avg

Import

89ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v1.17 · 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 0.092s · 17.9MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.5s · import 0.086s · 18MB

16MB installed

● package 16MB

Code

Verified usage

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

fastcov

✓ import fastcov

✗ from fastcov import fastcov

fastcov is a module, not a class; calling `fastcov.main()` is typical.

Run fastcov as a subprocess to generate lcov info output with branch coverage, excluding test files.

import subprocess subprocess.run(['fastcov', '--gcov', 'gcov', '--lcov', '-o', 'coverage.info', '--exclude', 'test', '--branch-coverage'], check=True)

fastcov --version

Debug

Known issues

breakingExit codes shifted in v1.7 to start at 3 (codes 1-2 reserved for shells). If you rely on exit codes, update your checks.

fix

Check for exit codes 3+ for failures, or use `--version` to detect version.

affects: >=1.7

deprecatedgcov shortform flags like `-i` (for intermediate format) may cause issues with GCC 11+. fastcov 1.14+ uses longform flags, but older versions might break.

fix

Upgrade to >=1.14 or set GCOV_PREFIX to include longform flags: `--gcov gcov --stdout --long-filename --preserve-paths`.

affects: <1.14

gotchaUsing `--zerocounters` with `--process-gcno` simultaneously can delete .gcno files (fixed in v1.14). Always verify you have backups.

fix

Upgrade to >=1.14, or avoid combining those flags.

affects: <1.14

gotchaIf gcov crashes or is killed, fastcov may hang forever (fixed in v1.11). For older versions, set a timeout on the subprocess call.

fix

Upgrade to >=1.11 or wrap subprocess with timeout.

affects: <1.11

Errors

Common errors & fixes

fastcov: error: unrecognized arguments: --branch-coverage

Older versions of fastcov did not support `--branch-coverage`; it was added later.

fix

Use `--branch` instead (alias) or upgrade fastcov to >=1.10.

AttributeError: module 'fastcov' has no attribute 'main'

Trying to call `fastcov.main()` directly but the module is not designed that way; fastcov is intended to be run as a CLI tool.

fix

Use subprocess to invoke fastcov or import the internal modules directly (not recommended).

KeyError: 'source_files'

Parsing fastcov's internal JSON output format yourself; the format changed in v1.5 to support test names.

fix

Use the lcov info output (`--lcov -o output.info`) or rely on the official fastcov JSON schema (if you must).

Upgrade

Version history

1.17latest on PyPI · released May 29, 2026

Audit

Dependencies

No dependency data recorded yet.

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/RPGillespie6/fastcov ↗

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