Change Log


  • numeric literals are now formatted by Black (#452, #461, #464, #469):
    • numeric literals are normalized to include _ separators on Python 3.6+ code
    • added --skip-numeric-underscore-normalization to disable the above behavior and leave numeric underscores as they were in the input
    • code with _ in numeric literals is recognized as Python 3.6+
    • most letters in numeric literals are lowercased (e.g., in 1e10, 0x01)
    • hexadecimal digits are always uppercased (e.g. 0xBADC0DE)
  • added blackd, see its documentation for more info (#349)
  • adjacent string literals are now correctly split into multiple lines (#463)
  • trailing comma is now added to single imports that don’t fit on a line (#250)
  • cache is now populated when --check is successful for a file which speeds up consecutive checks of properly formatted unmodified files (#448)
  • whitespace at the beginning of the file is now removed (#399)
  • fixed mangling pweave and Spyder IDE special comments (#532)
  • fixed unstable formatting when unpacking big tuples (#267)
  • fixed parsing of __future__ imports with renames (#389)
  • fixed scope of # fmt: off when directly preceding yield and other nodes (#385)
  • fixed formatting of lambda expressions with default arguments (#468)
  • fixed async for statements: Black no longer breaks them into separate lines (#372)
  • note: the Vim plugin stopped registering ,= as a default chord as it turned out to be a bad idea (#415)


  • hotfix: don’t freeze when multiple comments directly precede # fmt: off (#371)


  • typing stub files (.pyi) now have blank lines added after constants (#340)
  • # fmt: off and # fmt: on are now much more dependable:
    • they now work also within bracket pairs (#329)
    • they now correctly work across function/class boundaries (#335)
    • they now work when an indentation block starts with empty lines or misaligned comments (#334)
  • made Click not fail on invalid environments; note that Click is right but the likelihood we’ll need to access non-ASCII file paths when dealing with Python source code is low (#277)
  • fixed improper formatting of f-strings with quotes inside interpolated expressions (#322)
  • fixed unnecessary slowdown when long list literals where found in a file
  • fixed unnecessary slowdown on AST nodes with very many siblings
  • fixed cannibalizing backslashes during string normalization
  • fixed a crash due to symbolic links pointing outside of the project directory (#338)


  • added --config (#65)
  • added -h equivalent to --help (#316)
  • fixed improper unmodified file caching when -S was used
  • fixed extra space in string unpacking (#305)
  • fixed formatting of empty triple quoted strings (#313)
  • fixed unnecessary slowdown in comment placement calculation on lines without comments


  • hotfix: don’t output human-facing information on stdout (#299)
  • hotfix: don’t output cake emoji on non-zero return code (#300)


  • added --include and --exclude (#270)
  • added --skip-string-normalization (#118)
  • added --verbose (#283)
  • the header output in --diff now actually conforms to the unified diff spec
  • fixed long trivial assignments being wrapped in unnecessary parentheses (#273)
  • fixed unnecessary parentheses when a line contained multiline strings (#232)
  • fixed stdin handling not working correctly if an old version of Click was used (#276)
  • Black now preserves line endings when formatting a file in place (#258)


  • added --pyi (#249)
  • added --py36 (#249)
  • Python grammar pickle caches are stored with the formatting caches, making Black work in environments where site-packages is not user-writable (#192)
  • Black now enforces a PEP 257 empty line after a class-level docstring (and/or fields) and the first method
  • fixed invalid code produced when standalone comments were present in a trailer that was omitted from line splitting on a large expression (#237)
  • fixed optional parentheses being removed within # fmt: off sections (#224)
  • fixed invalid code produced when stars in very long imports were incorrectly wrapped in optional parentheses (#234)
  • fixed unstable formatting when inline comments were moved around in a trailer that was omitted from line splitting on a large expression (#238)
  • fixed extra empty line between a class declaration and the first method if no class docstring or fields are present (#219)
  • fixed extra empty line between a function signature and an inner function or inner class (#196)


  • call chains are now formatted according to the fluent interfaces style (#67)
  • data structure literals (tuples, lists, dictionaries, and sets) are now also always exploded like imports when they don’t fit in a single line (#152)
  • slices are now formatted according to PEP 8 (#178)
  • parentheses are now also managed automatically on the right-hand side of assignments and return statements (#140)
  • math operators now use their respective priorities for delimiting multiline expressions (#148)
  • optional parentheses are now omitted on expressions that start or end with a bracket and only contain a single operator (#177)
  • empty parentheses in a class definition are now removed (#145, #180)
  • string prefixes are now standardized to lowercase and u is removed on Python 3.6+ only code and Python 2.7+ code with the unicode_literals future import (#188, #198, #199)
  • typing stub files (.pyi) are now formatted in a style that is consistent with PEP 484 (#207, #210)
  • progress when reformatting many files is now reported incrementally
  • fixed trailers (content with brackets) being unnecessarily exploded into their own lines after a dedented closing bracket (#119)
  • fixed an invalid trailing comma sometimes left in imports (#185)
  • fixed non-deterministic formatting when multiple pairs of removable parentheses were used (#183)
  • fixed multiline strings being unnecessarily wrapped in optional parentheses in long assignments (#215)
  • fixed not splitting long from-imports with only a single name
  • fixed Python 3.6+ file discovery by also looking at function calls with unpacking. This fixed non-deterministic formatting if trailing commas where used both in function signatures with stars and function calls with stars but the former would be reformatted to a single line.
  • fixed crash on dealing with optional parentheses (#193)
  • fixed “is”, “is not”, “in”, and “not in” not considered operators for splitting purposes
  • fixed crash when dead symlinks where encountered


  • don’t populate the cache on --check (#175)


  • added a “cache”; files already reformatted that haven’t changed on disk won’t be reformatted again (#109)
  • --check and --diff are no longer mutually exclusive (#149)
  • generalized star expression handling, including double stars; this fixes multiplication making expressions “unsafe” for trailing commas (#132)
  • Black no longer enforces putting empty lines behind control flow statements (#90)
  • Black now splits imports like “Mode 3 + trailing comma” of isort (#127)
  • fixed comment indentation when a standalone comment closes a block (#16, #32)
  • fixed standalone comments receiving extra empty lines if immediately preceding a class, def, or decorator (#56, #154)
  • fixed --diff not showing entire path (#130)
  • fixed parsing of complex expressions after star and double stars in function calls (#2)
  • fixed invalid splitting on comma in lambda arguments (#133)
  • fixed missing splits of ternary expressions (#141)


  • fixed parsing of unaligned standalone comments (#99, #112)
  • fixed placement of dictionary unpacking inside dictionary literals (#111)
  • Vim plugin now works on Windows, too
  • fixed unstable formatting when encountering unnecessarily escaped quotes in a string (#120)


  • added --quiet (#78)
  • added automatic parentheses management (#4)
  • added pre-commit integration (#103, #104)
  • fixed reporting on --check with multiple files (#101, #102)
  • fixed removing backslash escapes from raw strings (#100, #105)


  • added --diff (#87)
  • add line breaks before all delimiters, except in cases like commas, to better comply with PEP 8 (#73)
  • standardize string literals to use double quotes (almost) everywhere (#75)
  • fixed handling of standalone comments within nested bracketed expressions; Black will no longer produce super long lines or put all standalone comments at the end of the expression (#22)
  • fixed 18.3a4 regression: don’t crash and burn on empty lines with trailing whitespace (#80)
  • fixed 18.3a4 regression: # yapf: disable usage as trailing comment would cause Black to not emit the rest of the file (#95)
  • when CTRL+C is pressed while formatting many files, Black no longer freaks out with a flurry of asyncio-related exceptions
  • only allow up to two empty lines on module level and only single empty lines within functions (#74)


  • # fmt: off and # fmt: on are implemented (#5)
  • automatic detection of deprecated Python 2 forms of print statements and exec statements in the formatted file (#49)
  • use proper spaces for complex expressions in default values of typed function arguments (#60)
  • only return exit code 1 when –check is used (#50)
  • don’t remove single trailing commas from square bracket indexing (#59)
  • don’t omit whitespace if the previous factor leaf wasn’t a math operator (#55)
  • omit extra space in kwarg unpacking if it’s the first argument (#46)
  • omit extra space in Sphinx auto-attribute comments (#68)


  • don’t remove single empty lines outside of bracketed expressions (#19)
  • added ability to pipe formatting from stdin to stdin (#25)
  • restored ability to format code with legacy usage of async as a name (#20, #42)
  • even better handling of numpy-style array indexing (#33, again)


  • changed positioning of binary operators to occur at beginning of lines instead of at the end, following a recent change to PEP 8 (#21)
  • ignore empty bracket pairs while splitting. This avoids very weirdly looking formattings (#34, #35)
  • remove a trailing comma if there is a single argument to a call
  • if top level functions were separated by a comment, don’t put four empty lines after the upper function
  • fixed unstable formatting of newlines with imports
  • fixed unintentional folding of post scriptum standalone comments into last statement if it was a simple statement (#18, #28)
  • fixed missing space in numpy-style array indexing (#33)
  • fixed spurious space after star-based unary expressions (#31)


  • added --check
  • only put trailing commas in function signatures and calls if it’s safe to do so. If the file is Python 3.6+ it’s always safe, otherwise only safe if there are no *args or **kwargs used in the signature or call. (#8)
  • fixed invalid spacing of dots in relative imports (#6, #13)
  • fixed invalid splitting after comma on unpacked variables in for-loops (#23)
  • fixed spurious space in parenthesized set expressions (#7)
  • fixed spurious space after opening parentheses and in default arguments (#14, #17)
  • fixed spurious space after unary operators when the operand was a complex expression (#15)


  • first published version, Happy 🍰 Day 2018!
  • alpha quality
  • date-versioned (see: