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YAPF

Introduction

Most of the current formatters for Python --- e.g., autopep8, and pep8ify --- are made to remove lint errors from code. This has some obvious limitations. For instance, code that conforms to the PEP 8 guidelines may not be reformatted. But it doesn't mean that the code looks good.

YAPF takes a different approach. It's based off of 'clang-format', developed by Daniel Jasper. In essence, the algorithm takes the code and reformats it to the best formatting that conforms to the style guide, even if the original code didn't violate the style guide. The idea is also similar to the 'gofmt' tool for the Go programming language: end all holy wars about formatting - if the whole codebase of a project is simply piped through YAPF whenever modifications are made, the style remains consistent throughout the project and there's no point arguing about style in every code review.

The ultimate goal is that the code YAPF produces is as good as the code that a programmer would write if they were following the style guide. It takes away some of the drudgery of maintaining your code.

Installation

To install YAPF from PyPI:

$ pip install yapf

(optional) If you are using Python 2.7 and want to enable multiprocessing:

$ pip install futures

YAPF is still considered in "alpha" stage, and the released version may change often; therefore, the best way to keep up-to-date with the latest development is to clone this repository.

Note that if you intend to use YAPF as a command-line tool rather than as a library, installation is not necessary. YAPF supports being run as a directory by the Python interpreter. If you cloned/unzipped YAPF into DIR, it's possible to run:

$ PYTHONPATH=DIR python DIR/yapf [options] ...

Python versions

YAPF supports Python 2.7 and 3.6.4+. (Note that some Python 3 features may fail to parse with Python versions before 3.6.4.)

YAPF requires the code it formats to be valid Python for the version YAPF itself runs under. Therefore, if you format Python 3 code with YAPF, run YAPF itself under Python 3 (and similarly for Python 2).

Usage

Options:

usage: yapf [-h] [-v] [-d | -i | -q] [-r | -l START-END] [-e PATTERN]
            [--style STYLE] [--style-help] [--no-local-style] [-p]
            [-vv]
            [files ...]

Formatter for Python code.

positional arguments:
  files                 reads from stdin when no files are specified.

optional arguments:
  -h, --help            show this help message and exit
  -v, --version         show program's version number and exit
  -d, --diff            print the diff for the fixed source
  -i, --in-place        make changes to files in place
  -q, --quiet           output nothing and set return value
  -r, --recursive       run recursively over directories
  -l START-END, --lines START-END
                        range of lines to reformat, one-based
  -e PATTERN, --exclude PATTERN
                        patterns for files to exclude from formatting
  --style STYLE         specify formatting style: either a style name (for
                        example "pep8" or "google"), or the name of a file
                        with style settings.  The default is pep8 unless a
                        .style.yapf or setup.cfg or pyproject.toml file
                        located in the same directory as the source or one
                        of its parent directories (for stdin, the current
                        directory is used).
  --style-help          show style settings and exit; this output can be
                        saved to .style.yapf to make your settings
                        permanent
  --no-local-style      don't search for local style definition
  -p, --parallel        run YAPF in parallel when formatting multiple
                        files. Requires concurrent.futures in Python 2.X
  -vv, --verbose        print out file names while processing

Return Codes

Normally YAPF returns zero on successful program termination and non-zero otherwise.

If --diff is supplied, YAPF returns zero when no changes were necessary, non-zero otherwise (including program error). You can use this in a CI workflow to test that code has been YAPF-formatted.

Excluding files from formatting (.yapfignore or pyproject.toml)

In addition to exclude patterns provided on commandline, YAPF looks for additional patterns specified in a file named .yapfignore or pyproject.toml located in the working directory from which YAPF is invoked.

.yapfignore's syntax is similar to UNIX's filename pattern matching:

*       matches everything
?       matches any single character
[seq]   matches any character in seq
[!seq]  matches any character not in seq

Note that no entry should begin with ./.

If you use pyproject.toml, exclude patterns are specified by ignore_pattens key in [tool.yapfignore] section. For example:

[tool.yapfignore]
ignore_patterns = [
  "temp/**/*.py",
  "temp2/*.py"
]

Formatting style

The formatting style used by YAPF is configurable and there are many "knobs" that can be used to tune how YAPF does formatting. See the style.py module for the full list.

To control the style, run YAPF with the --style argument. It accepts one of the predefined styles (e.g., pep8 or google), a path to a configuration file that specifies the desired style, or a dictionary of key/value pairs.

The config file is a simple listing of (case-insensitive) key = value pairs with a [style] heading. For example:

[style]
based_on_style = pep8
spaces_before_comment = 4
split_before_logical_operator = true

The based_on_style setting determines which of the predefined styles this custom style is based on (think of it like subclassing). Four styles are predefined:

• pep8 (default)
• google (based off of the Google Python Style Guide)
• yapf (for use with Google open source projects)
• facebook

See _STYLE_NAME_TO_FACTORY in style.py for details.

It's also possible to do the same on the command line with a dictionary. For example:

--style='{based_on_style: pep8, indent_width: 2}'

This will take the pep8 base style and modify it to have two space indentations.

YAPF will search for the formatting style in the following manner:

1. Specified on the command line
2. In the [style] section of a .style.yapf file in either the current directory or one of its parent directories.
3. In the [yapf] section of a setup.cfg file in either the current directory or one of its parent directories.
4. In the [tool.yapf] section of a pyproject.toml file in either the current directory or one of its parent directories.
5. In the [style] section of a ~/.config/yapf/style file in your home directory.

If none of those files are found, the default style is used (PEP8).

Example

An example of the type of formatting that YAPF can do, it will take this ugly code:

x = {  'a':37,'b':42,

'c':927}

y = 'hello ''world'
z = 'hello '+'world'
a = 'hello {}'.format('world')
class foo  (     object  ):
  def f    (self   ):
    return       37*-+2
  def g(self, x,y=42):
      return y
def f  (   a ) :
  return      37+-+a[42-x :  y**3]

and reformat it into:

x = {'a': 37, 'b': 42, 'c': 927}

y = 'hello ' 'world'
z = 'hello ' + 'world'
a = 'hello {}'.format('world')


class foo(object):
    def f(self):
        return 37 * -+2

    def g(self, x, y=42):
        return y


def f(a):
    return 37 + -+a[42 - x:y**3]

Example as a module

The two main APIs for calling YAPF are FormatCode and FormatFile, these share several arguments which are described below:

>>> from yapf.yapflib.yapf_api import FormatCode  # reformat a string of code

>>> formatted_code, changed = FormatCode("f ( a = 1, b = 2 )")
>>> formatted_code
'f(a=1, b=2)\n'
>>> changed
True

A style_config argument: Either a style name or a path to a file that contains formatting style settings. If None is specified, use the default style as set in style.DEFAULT_STYLE_FACTORY.

>>> FormatCode("def g():\n  return True", style_config='pep8')[0]
'def g():\n    return True\n'

A lines argument: A list of tuples of lines (ints), [start, end], that we want to format. The lines are 1-based indexed. It can be used by third-party code (e.g., IDEs) when reformatting a snippet of code rather than a whole file.

>>> FormatCode("def g( ):\n    a=1\n    b = 2\n    return a==b", lines=[(1, 1), (2, 3)])[0]
'def g():\n    a = 1\n    b = 2\n    return a==b\n'

A print_diff (bool): Instead of returning the reformatted source, return a diff that turns the formatted source into reformatted source.

>>> print(FormatCode("a==b", filename="foo.py", print_diff=True)[0])
--- foo.py (original)
+++ foo.py (reformatted)
@@ -1 +1 @@
-a==b
+a == b

Note: the filename argument for FormatCode is what is inserted into the diff, the default is <unknown>.

FormatFile returns reformatted code from the passed file along with its encoding:

>>> from yapf.yapflib.yapf_api import FormatFile  # reformat a file

>>> print(open("foo.py").read())  # contents of file
a==b

>>> reformatted_code, encoding, changed = FormatFile("foo.py")
>>> formatted_code
'a == b\n'
>>> encoding
'utf-8'
>>> changed
True

The in_place argument saves the reformatted code back to the file:

>>> FormatFile("foo.py", in_place=True)[:2]
(None, 'utf-8')

>>> print(open("foo.py").read())  # contents of file (now fixed)
a == b

Formatting diffs

Options:

usage: yapf-diff [-h] [-i] [-p NUM] [--regex PATTERN] [--iregex PATTERN][-v]
                 [--style STYLE] [--binary BINARY]

This script reads input from a unified diff and reformats all the changed
lines. This is useful to reformat all the lines touched by a specific patch.
Example usage for git/svn users:

  git diff -U0 --no-color --relative HEAD^ | yapf-diff -i
  svn diff --diff-cmd=diff -x-U0 | yapf-diff -p0 -i

It should be noted that the filename contained in the diff is used
unmodified to determine the source file to update. Users calling this script
directly should be careful to ensure that the path in the diff is correct
relative to the current working directory.

optional arguments:
  -h, --help            show this help message and exit
  -i, --in-place        apply edits to files instead of displaying a diff
  -p NUM, --prefix NUM  strip the smallest prefix containing P slashes
  --regex PATTERN       custom pattern selecting file paths to reformat
                        (case sensitive, overrides -iregex)
  --iregex PATTERN      custom pattern selecting file paths to reformat
                        (case insensitive, overridden by -regex)
  -v, --verbose         be more verbose, ineffective without -i
  --style STYLE         specify formatting style: either a style name (for
                        example "pep8" or "google"), or the name of a file
                        with style settings. The default is pep8 unless a
                        .style.yapf or setup.cfg or pyproject.toml file
                        located in the same directory as the source or one of
                        its parent directories (for stdin, the current
                        directory is used).
  --binary BINARY       location of binary to use for YAPF

Knobs

ALIGN_CLOSING_BRACKET_WITH_VISUAL_INDENT

Align closing bracket with visual indentation.

ALLOW_MULTILINE_LAMBDAS

Allow lambdas to be formatted on more than one line.

ALLOW_MULTILINE_DICTIONARY_KEYS

Allow dictionary keys to exist on multiple lines. For example:

x = {
    ('this is the first element of a tuple',
     'this is the second element of a tuple'):
         value,
}

ALLOW_SPLIT_BEFORE_DEFAULT_OR_NAMED_ASSIGNS

Allow splitting before a default / named assignment in an argument list.

ALLOW_SPLIT_BEFORE_DICT_VALUE

Allow splits before the dictionary value.

ARITHMETIC_PRECEDENCE_INDICATION

Let spacing indicate operator precedence. For example:

a = 1 * 2 + 3 / 4
b = 1 / 2 - 3 * 4
c = (1 + 2) * (3 - 4)
d = (1 - 2) / (3 + 4)
e = 1 * 2 - 3
f = 1 + 2 + 3 + 4

will be formatted as follows to indicate precedence:

a = 1*2 + 3/4
b = 1/2 - 3*4
c = (1+2) * (3-4)
d = (1-2) / (3+4)
e = 1*2 - 3
f = 1 + 2 + 3 + 4

BLANK_LINE_BEFORE_NESTED_CLASS_OR_DEF

Insert a blank line before a def or class immediately nested within another def or class. For example:

class Foo:
                   # <------ this blank line
    def method():
        pass

BLANK_LINE_BEFORE_MODULE_DOCSTRING

Insert a blank line before a module docstring.

BLANK_LINE_BEFORE_CLASS_DOCSTRING

Insert a blank line before a class-level docstring.

BLANK_LINES_AROUND_TOP_LEVEL_DEFINITION

Sets the number of desired blank lines surrounding top-level function and class definitions. For example:

class Foo:
    pass
                   # <------ having two blank lines here
                   # <------ is the default setting
class Bar:
    pass

BLANK_LINES_BETWEEN_TOP_LEVEL_IMPORTS_AND_VARIABLES

Sets the number of desired blank lines between top-level imports and variable definitions. Useful for compatibility with tools like isort.

COALESCE_BRACKETS

Do not split consecutive brackets. Only relevant when DEDENT_CLOSING_BRACKETS or INDENT_CLOSING_BRACKETS is set. For example:

call_func_that_takes_a_dict(
    {
        'key1': 'value1',
        'key2': 'value2',
    }
)

would reformat to:

call_func_that_takes_a_dict({
    'key1': 'value1',
    'key2': 'value2',
})

COLUMN_LIMIT

The column limit (or max line-length)

CONTINUATION_ALIGN_STYLE

The style for continuation alignment. Possible values are:

• SPACE: Use spaces for continuation alignment. This is default behavior.
• FIXED: Use fixed number (CONTINUATION_INDENT_WIDTH) of columns (ie: CONTINUATION_INDENT_WIDTH/INDENT_WIDTH tabs or CONTINUATION_INDENT_WIDTH spaces) for continuation alignment.
• VALIGN-RIGHT: Vertically align continuation lines to multiple of INDENT_WIDTH columns. Slightly right (one tab or a few spaces) if cannot vertically align continuation lines with indent characters.

CONTINUATION_INDENT_WIDTH

Indent width used for line continuations.

DEDENT_CLOSING_BRACKETS

Put closing brackets on a separate line, dedented, if the bracketed expression can't fit in a single line. Applies to all kinds of brackets, including function definitions and calls. For example:

config = {
    'key1': 'value1',
    'key2': 'value2',
}  # <--- this bracket is dedented and on a separate line

time_series = self.remote_client.query_entity_counters(
    entity='dev3246.region1',
    key='dns.query_latency_tcp',
    transform=Transformation.AVERAGE(window=timedelta(seconds=60)),
    start_ts=now()-timedelta(days=3),
    end_ts=now(),
)  # <--- this bracket is dedented and on a separate line

DISABLE_ENDING_COMMA_HEURISTIC

Disable the heuristic which places each list element on a separate line if the list is comma-terminated.

EACH_DICT_ENTRY_ON_SEPARATE_LINE

Place each dictionary entry onto its own line.

FORCE_MULTILINE_DICT

Respect EACH_DICT_ENTRY_ON_SEPARATE_LINE even if the line is shorter than COLUMN_LIMIT.

I18N_COMMENT

The regex for an internationalization comment. The presence of this comment stops reformatting of that line, because the comments are required to be next to the string they translate.

I18N_FUNCTION_CALL

The internationalization function call names. The presence of this function stops reformatting on that line, because the string it has cannot be moved away from the i18n comment.

INDENT_DICTIONARY_VALUE

Indent the dictionary value if it cannot fit on the same line as the dictionary key. For example:

config = {
    'key1':
        'value1',
    'key2': value1 +
            value2,
}

INDENT_WIDTH

The number of columns to use for indentation.

INDENT_BLANK_LINES

Set to True to prefer indented blank lines rather than empty

INDENT_CLOSING_BRACKETS

Put closing brackets on a separate line, indented, if the bracketed expression can't fit in a single line. Applies to all kinds of brackets, including function definitions and calls. For example:

config = {
    'key1': 'value1',
    'key2': 'value2',
    }  # <--- this bracket is indented and on a separate line

time_series = self.remote_client.query_entity_counters(
    entity='dev3246.region1',
    key='dns.query_latency_tcp',
    transform=Transformation.AVERAGE(window=timedelta(seconds=60)),
    start_ts=now()-timedelta(days=3),
    end_ts=now(),
    )  # <--- this bracket is indented and on a separate line

JOIN_MULTIPLE_LINES

Join short lines into one line. E.g., single line if statements.

NO_SPACES_AROUND_SELECTED_BINARY_OPERATORS

Do not include spaces around selected binary operators. For example:

1 + 2 * 3 - 4 / 5

will be formatted as follows when configured with *, /:

1 + 2*3 - 4/5

SPACES_AROUND_POWER_OPERATOR

Set to True to prefer using spaces around **.

SPACES_AROUND_DEFAULT_OR_NAMED_ASSIGN

Set to True to prefer spaces around the assignment operator for default or keyword arguments.

SPACES_AROUND_DICT_DELIMITERS

Adds a space after the opening '{' and before the ending '}' dict delimiters.

{1: 2}

will be formatted as:

{ 1: 2 }

SPACES_AROUND_LIST_DELIMITERS

Adds a space after the opening '[' and before the ending ']' list delimiters.

[1, 2]

will be formatted as:

[ 1, 2 ]

SPACES_AROUND_SUBSCRIPT_COLON

Use spaces around the subscript / slice operator. For example:

my_list[1 : 10 : 2]

SPACES_AROUND_TUPLE_DELIMITERS

Adds a space after the opening '(' and before the ending ')' tuple delimiters.

(1, 2, 3)

will be formatted as:

( 1, 2, 3 )

SPACES_BEFORE_COMMENT

The number of spaces required before a trailing comment. This can be a single value (representing the number of spaces before each trailing comment) or list of of values (representing alignment column values; trailing comments within a block will be aligned to the first column value that is greater than the maximum line length within the block). For example:

With spaces_before_comment=5:

1 + 1 # Adding values

will be formatted as:

1 + 1     # Adding values <-- 5 spaces between the end of the statement and comment

With spaces_before_comment=15, 20:

1 + 1 # Adding values
two + two # More adding

longer_statement # This is a longer statement
short # This is a shorter statement

a_very_long_statement_that_extends_beyond_the_final_column # Comment
short # This is a shorter statement

will be formatted as:

1 + 1          # Adding values <-- end of line comments in block aligned to col 15
two + two      # More adding

longer_statement    # This is a longer statement <-- end of line comments in block aligned to col 20
short               # This is a shorter statement

a_very_long_statement_that_extends_beyond_the_final_column  # Comment <-- the end of line comments are aligned based on the line length
short                                                       # This is a shorter statement

SPACE_BETWEEN_ENDING_COMMA_AND_CLOSING_BRACKET

Insert a space between the ending comma and closing bracket of a list, etc.

SPACE_INSIDE_BRACKETS

Use spaces inside brackets, braces, and parentheses. For example:

method_call( 1 )
my_dict[ 3 ][ 1 ][ get_index( *args, **kwargs ) ]
my_set = { 1, 2, 3 }

SPLIT_ARGUMENTS_WHEN_COMMA_TERMINATED

Split before arguments if the argument list is terminated by a comma.

SPLIT_ALL_COMMA_SEPARATED_VALUES

If a comma separated list (dict, list, tuple, or function def) is on a line that is too long, split such that each element is on a separate line.

SPLIT_ALL_TOP_LEVEL_COMMA_SEPARATED_VALUES

Variation on SPLIT_ALL_COMMA_SEPARATED_VALUES in which, if a subexpression with a comma fits in its starting line, then the subexpression is not split. This avoids splits like the one for b in this code:

abcdef(
    aReallyLongThing: int,
    b: [Int,
        Int])

With the new knob this is split as:

abcdef(
    aReallyLongThing: int,
    b: [Int, Int])

SPLIT_BEFORE_BITWISE_OPERATOR

Set to True to prefer splitting before &, | or ^ rather than after.

SPLIT_BEFORE_ARITHMETIC_OPERATOR

Set to True to prefer splitting before +, -, *, /, //, or @ rather than after.

SPLIT_BEFORE_CLOSING_BRACKET

Split before the closing bracket if a list or dict literal doesn't fit on a single line.

SPLIT_BEFORE_DICT_SET_GENERATOR

Split before a dictionary or set generator (comp_for). For example, note the split before the for:

foo = {
    variable: 'Hello world, have a nice day!'
    for variable in bar if variable != 42
}

SPLIT_BEFORE_DOT

Split before the . if we need to split a longer expression:

foo = ('This is a really long string: {}, {}, {}, {}'.format(a, b, c, d))

would reformat to something like:

foo = ('This is a really long string: {}, {}, {}, {}'
       .format(a, b, c, d))

SPLIT_BEFORE_EXPRESSION_AFTER_OPENING_PAREN

Split after the opening paren which surrounds an expression if it doesn't fit on a single line.

SPLIT_BEFORE_FIRST_ARGUMENT

If an argument / parameter list is going to be split, then split before the first argument.

SPLIT_BEFORE_LOGICAL_OPERATOR

Set to True to prefer splitting before and or or rather than after.

SPLIT_BEFORE_NAMED_ASSIGNS

Split named assignments onto individual lines.

SPLIT_COMPL