Python Formatter
What is Python Formatting?
The Python Formatter reorganizes Python code with consistent indentation, line breaks, and readable structure. In Python, indentation is part of the syntax, so badly pasted or mixed-format code can be more than ugly; it can change behavior or cause errors. This tool helps with scripts, notebook excerpts, generated code, learning examples, reviews, and small refactors by making functions, classes, imports, lists, dictionaries, and nested expressions easier to scan. Formatting does not fix logic bugs, type errors, missing dependencies, runtime environment problems, or API misuse. In real projects, the result should align with Black, Ruff, isort, or the team’s established style rules.
How to Use
How to use
- Paste or type Python code in the left input box
- Select indent size (2 spaces, 4 spaces, or Tab)
- Click 'Format' to beautify code, or 'Minify' to compress
- View results on the right (with syntax highlighting)
- Click 'Copy' to copy to clipboard
Options Description
Python Tips
- Python is indentation-sensitive, so inspect formatted control blocks before copying the result back into a project.
- Formatting does not run type checks, imports, or tests. Use your normal Python tooling for behavior and dependency validation.
Use Cases
Technical Principle
Python is one of the few mainstream languages that uses indentation rather than braces to define code blocks. Consecutive statements with the same indentation belong to the same block; one space more or less and the semantics change. This design makes the visual structure of the code match its logic, but it requires the formatter to identify the logical levels precisely. The formatter first scans the code with the tokenize module or a custom lexer, treating the leading whitespace of each line as indentation information. Statements inside brackets (round, square, or curly) can span multiple lines, in which case indentation is determined by the bracket depth rather than the leading whitespace. Whitespace inside string literals (triple-quoted, single-quoted) must not be touched, otherwise the string value changes. PEP 8 is Python's official style guide, specifying 4-space indentation, a maximum line length of 79 characters, spaces around operators, grouped imports, and naming conventions. Black is the leading example of the no-configuration school of formatters: it forces double-quoted strings, trailing commas, and an 88-character line length, with strict and non-configurable rules. yapf is closer to the Google style and is configurable.
- Indentation semantics: Python uses leading whitespace to decide code blocks; the same indentation means the same block, a change of indentation switches scope
- PEP 8 rules: 4-space indentation, line width of 79 characters, spaces around operators, CapWords for class names, snake_case for function names
- Bracket line breaks: statements inside brackets (round, square, curly) can wrap, and indentation is determined by the bracket depth rather than the leading whitespace
- String boundaries: whitespace inside triple-quoted strings and docstrings must not be changed, otherwise it breaks the literal content
- Black style: zero configuration, not customizable, forces double quotes, trailing commas, 88 characters per line, identical across the whole project
- Type annotations: introduced in PEP 484; the formatter preserves the proper spacing around -> return types and parameter : type annotations
Examples
Formatting Function Definitions
Input: def add(a,b):
return a+b
def subtract(a,b):
return a-b
Output:
def add(a, b):
return a + b
def subtract(a, b):
return a - bFormatting List Comprehensions
Input: result=[x*x for x in range(10) if x%2==0]
result2={k:v for k,v in items if v>0}
Output:
result = [x * x for x in range(10) if x % 2 == 0]
result2 = {k: v for k, v in items if v > 0}Formatting a Class Definition
Input: class User:
def __init__(self,name,email):
self.name=name
self.email=email
def __repr__(self):
return f"User({self.name})"
Output:
class User:
def __init__(self, name, email):
self.name = name
self.email = email
def __repr__(self):
return f"User({self.name})"FAQ
Which Python style does it use?
Most builds default to PEP 8 conventions, often via Black: 88-column line width, double-quoted strings, no trailing semicolons. Black is opinionated - it strips most config knobs to give a consistent project-wide style. autopep8 and yapf have more options if you need flexibility.
Does indentation matter for the formatter?
Yes - Python indentation defines block structure. The formatter respects existing block boundaries; if your input has mixed tabs/spaces or wrong indent levels, parsing fails before formatting runs.
Will it fix import order?
Black, autopep8, and yapf only handle whitespace. To sort and group imports, use isort (or ruff --fix). Some pages combine the two; read the configuration to know what's actually applied.
Are type hints supported?
Yes for modern parsers. Type annotations on function signatures, variables, and class attributes (PEP 526, 484, 612) format correctly. Very new syntax (PEP 695 generic syntax in 3.12+) needs a recent parser; older builds may stumble.
Is my code uploaded?
No. Formatting runs in your browser using a JavaScript implementation of the Python AST. Pasted code is not transmitted.
Will the result match black on my CI?
Close but not always identical. Different Black versions can format slightly differently (Black updates its rules regularly). For CI consistency, run the same Black version locally and in CI; treat this page as a quick visual check.
Why does it wrap long lines into multiple lines?
PEP 8 and Black aim for ≤88 characters per line. Long expressions, function calls with many args, and chained method calls get split across lines for readability. Adjust the line-width option if your team uses 100 or 120.