Frequently Asked Questions#

The most common questions and issues users face are aggregated to this FAQ.

Why spaces? I prefer tabs#

PEP 8 recommends spaces over tabs, and they are used by most of the Python community. Black provides no options to configure the indentation style, and requests for such options will not be considered.

However, we recognise that using tabs is an accessibility issue as well. While the option will never be added to Black, visually impaired developers may find conversion tools such as expand/unexpand (for Linux) useful when contributing to Python projects. A workflow might consist of e.g. setting up appropriate pre-commit and post-merge git hooks, and scripting unexpand to run after applying Black.

Does Black have an API?#

Not yet. Black is fundamentally a command line tool. Many integrations are provided, but a Python interface is not one of them. A simple API is being planned though.

Is Black safe to use?#

Yes. Black is strictly about formatting, nothing else. Black strives to ensure that after formatting the AST is checked with limited special cases where the code is allowed to differ. If issues are found, an error is raised and the file is left untouched. Magical comments that influence linters and other tools, such as # noqa, may be moved by Black. See below for more details.

How stable is Black’s style?#

Stable. Black aims to enforce one style and one style only, with some room for pragmatism. See The Black Code Style for more details.

Starting in 2022, the formatting output will be stable for the releases made in the same year (other than unintentional bugs). It is possible to opt-in to the latest formatting styles, using the --preview flag.

Why is my file not formatted?#

Most likely because it is ignored in .gitignore or excluded with configuration. See file collection and discovery for details.

Why is my Jupyter Notebook cell not formatted?#

Black is timid about formatting Jupyter Notebooks. Cells containing any of the following will not be formatted:

  • automagics (e.g. pip install black)

  • non-Python cell magics (e.g. %%writeline). These can be added with the flag --python-cell-magics, e.g. black --python-cell-magics writeline hello.ipynb.

  • multiline magics, e.g.:

    %timeit f(1, \
            2, \
            3)
    
  • code which IPython’s TransformerManager would transform magics into, e.g.:

    get_ipython().system('ls')
    
  • invalid syntax, as it can’t be safely distinguished from automagics in the absence of a running IPython kernel.

Why are Flake8’s E203 and W503 violated?#

Because they go against PEP 8. E203 falsely triggers on list slices, and adhering to W503 hinders readability because operators are misaligned. Disable W503 and enable the disabled-by-default counterpart W504. E203 should be disabled while changes are still discussed.

Which Python versions does Black support?#

Currently the runtime requires Python 3.6-3.10. Formatting is supported for files containing syntax from Python 3.3 to 3.10. We promise to support at least all Python versions that have not reached their end of life. This is the case for both running Black and formatting code.

Support for formatting Python 2 code was removed in version 22.0. While we’ve made no plans to stop supporting older Python 3 minor versions immediately, their support might also be removed some time in the future without a deprecation period.

Why does my linter or typechecker complain after I format my code?#

Some linters and other tools use magical comments (e.g., # noqa, # type: ignore) to influence their behavior. While Black does its best to recognize such comments and leave them in the right place, this detection is not and cannot be perfect. Therefore, you’ll sometimes have to manually move these comments to the right place after you format your codebase with Black.

Can I run Black with PyPy?#

Yes, there is support for PyPy 3.7 and higher.

Why does Black not detect syntax errors in my code?#

Black is an autoformatter, not a Python linter or interpreter. Detecting all syntax errors is not a goal. It can format all code accepted by CPython (if you find an example where that doesn’t hold, please report a bug!), but it may also format some code that CPython doesn’t accept.

What is compiled: yes/no all about in the version output?#

While Black is indeed a pure Python project, we use mypyc to compile Black into a C Python extension, usually doubling performance. These compiled wheels are available for 64-bit versions of Windows, Linux (via the manylinux standard), and macOS across all supported CPython versions.

Platforms including musl-based and/or ARM Linux distributions, and ARM Windows are currently not supported. These platforms will fall back to the slower pure Python wheel available on PyPI.

If you are experiencing exceptionally weird issues or even segfaults, you can try passing --no-binary black to your pip install invocation. This flag excludes all wheels (including the pure Python wheel), so this command will use the sdist.