black/docs/faq.md

# Frequently Asked Questions

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

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## 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](/integrations/index.md) are provided, but a Python interface is not one
of them. A simple API is being [planned](https://github.com/psf/black/issues/779)
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](the_black_code_style/current_style.md#ast-before-and-after-formatting) 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](the_black_code_style/index.md) 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](usage_and_configuration/file_collection_and_discovery.md)
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. `%%writefile`). These can be added with the flag
  `--python-cell-magics`, e.g. `black --python-cell-magics writefile hello.ipynb`.
- multiline magics, e.g.:

  ```python
  %timeit f(1, \
          2, \
          3)
  ```

- code which `IPython`'s `TransformerManager` would transform magics into, e.g.:

  ```python
  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](the_black_code_style/current_style.md#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](https://github.com/PyCQA/pycodestyle/issues/373).

## Which Python versions does Black support?

Currently the runtime requires Python 3.8-3.11. Formatting is supported for files
containing syntax from Python 3.3 to 3.11. 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.

Runtime support for 3.7 was removed in version 23.7.0.

## 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 3.8 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.

(labels/mypyc-support)=

## 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].

[mypyc]: https://mypyc.readthedocs.io/en/latest/
[sdist]:
  https://packaging.python.org/en/latest/glossary/#term-Source-Distribution-or-sdist