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About the Python Formatter Online Python Formatter

Paste your Python code, choose a line length, and hit **Format** to instantly get clean, consistent output. The formatter follows Black-style, opinionated rules so you spend less time arguing about style and more time shipping features.

Why Use This Python Formatter

  • Black-style formatting for consistent, opinionated Python code
  • Configurable line length to control wrapping of long lines
  • Idempotent formatting – re-running on formatted code is a no-op
  • Safely reformats whitespace, indentation and layout without changing logic
  • Ideal for code reviews, pull requests and onboarding new team members
  • Works directly in the browser editor with syntax highlighting
  • Compatible with local Black usage so online and CI formatting stay aligned

🛠️ How to Use the Python Formatter for python-formatter

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1. Paste or upload your Python code

📥 Paste your code into the editor or drag-and-drop a `.py` file. The formatter assumes syntactically valid Python; if parsing fails, you’ll see an error instead of a formatted result.

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2. (Optional) Adjust line length

📏 Use the line-length setting to choose how aggressively long lines should be wrapped. Common values are 88 (Black default), 100 or 120 for wide monitors. Set it to 0 if you want to disable line-length-based wrapping.

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3. Format your code

✨ Click **Format**. The tool sends your code to a secure Black-style backend which normalizes indentation, blank lines, spacing and wrapping while preserving semantics.

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4. Review, copy or download

🔍 Compare before/after directly in the browser. When you’re happy with the result, copy the formatted code back into your project or download it as a `.py` file ready to commit.

Technical Specifications

Formatting Engine & Style

This formatter follows Black-style, opinionated rules so your Python code looks the same across files, machines and editors.

AspectBehaviorNotes
Indentation4 spaces per levelTabs are normalized to spaces in the formatted output.
QuotationConsistent quote styleStrings may be rewritten (for example, single to double quotes) to follow a uniform style.
ImportsGrouped and spaced consistentlyStandard library, third-party and local imports are separated with blank lines where applicable.
Blank linesNormalized around classes and functionsImproves readability by separating logical sections of the code.
IdempotencySame input → same outputRunning the formatter repeatedly does not produce additional changes.

Line Length & Wrapping

The main configurable parameter is the wrap / line-length setting (mapped to `wrapLineLength` in the tool options). It controls how long expressions and argument lists are wrapped while preserving code semantics.

SettingValue RangeEffect
wrapLineLength = 00Do not wrap based on line length; only minimal changes are applied.
wrapLineLength = 791–79Very compact style, suitable for strict terminals or narrow displays.
wrapLineLength = 80–10080–100Recommended range for most modern teams; balances readability and width.
wrapLineLength = 101–120101–120Looser layout for ultra-wide screens or heavily annotated code.

Supported Input & Limits

The formatter targets everyday Python scripts and modules used in web backends, CLIs, data science and teaching.

ParameterLimit / BehaviorNotes
File extensions.pyBest for stand-alone scripts, modules and simple package entry points.
MIME typestext/x-pythonUsed by the tool’s editor and upload handler to detect Python files.
Max input size≈ 2 MB sourceVery large files are better formatted with Black directly in your environment.
EncodingUTF-8 recommendedConvert from legacy encodings (e.g., latin-1) before formatting.

Execution Model & Safety

Formatting is performed on a secured backend so you can use Black-style rules in the browser without installing anything.

AspectBehaviorNotes
EngineServer-side Python formatter (Black-style)The UI forwards your code to `/api/python-formatter` with selected options.
TransportHTTPS POSTSource code is sent over an encrypted connection to the formatter backend.
Timeout~25 secondsRequests are aborted if formatting takes too long to guard against hung processes.
Error handlingClear error messagesInvalid Python or internal errors are surfaced back to the UI as readable error text.

Command Line Alternatives with Black

To keep your local workflow in sync with this online formatter, add Black to your virtualenv, editor and CI pipeline.

Linux / 🍎 macOS

Install Black using pip

pip install black

Installs the official Black formatter in your active Python environment.

Format a single file

black app.py

Rewrites `app.py` in place using Black’s default style.

Use a custom line length

black --line-length 100 app.py

Overrides the default line length to match your project’s conventions.

Windows (PowerShell / CMD)

Install Black with the py launcher

py -m pip install black

Uses the Windows `py` launcher to add Black to your environment.

Format an entire project

black src/ tests/

Recursively formats all Python files under `src/` and `tests/`.

Integrate with pre-commit

pre-commit install && pre-commit run --all-files

Runs Black automatically on staged files before each commit.

Mirror the same line-length setting in this tool, your local Black config and your CI pipeline to avoid noisy reformatting diffs.

Practical Use Cases for the Python Formatter

Backend & API Development

Keep your Django, FastAPI, Flask or microservice projects readable and reviewable.

  • Normalize formatting on models, views and routers before merging.
  • Use the formatter as a last step before opening a pull request.
  • Apply a single style to both hand-written and generated code.
from   fastapi import  FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item( item_id:int , q:str|None=None):
    return {"item_id":item_id,"q":q}

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int, q: str | None = None) -> dict:
    return {"item_id": item_id, "q": q}

Data Science & Notebooks

Turn exploratory Jupyter cells into clean Python scripts ready for version control.

  • Clean up long pandas chains and numerical pipelines.
  • Standardize style across notebooks before exporting them as `.py` modules.
  • Present polished code in reports, blog posts and technical writeups.
import pandas as pd

df = pd.read_csv("data.csv")
df["ratio"]=df["a"] /(df["b"]+1e-9)
df=df.sort_values("ratio",ascending=False)

import pandas as pd

df = pd.read_csv("data.csv")
df["ratio"] = df["a"] / (df["b"] + 1e-9)
df = df.sort_values("ratio", ascending=False)

Teaching & Learning Python

Show learners what idiomatic Python looks like by auto-formatting examples and exercises.

  • Clean student submissions before grading to focus on logic and structure.
  • Demonstrate the difference between “works” and “readable” with before/after comparisons.
  • Use the formatter live when teaching PEP 8 and modern Python features.
x= 1
if   x>0:
 print("positive")

x = 1
if x > 0:
    print("positive")

❓ Frequently Asked Questions

❓Will the Python formatter change how my code behaves?

No. A Black-style formatter is designed to change only the presentation of valid Python code, not its behavior. It rewrites whitespace, indentation and layout while preserving the semantics of your program.

📏What line length should I choose when formatting Python code?

PEP 8 suggests 79 or 99 characters, while Black’s default is 88. Many teams use 88, 100 or 120 depending on their screens and preferences. The important part is to pick a single value and apply it consistently everywhere.

🧹How is this different from a Python linter?

A formatter rewrites code to follow a consistent style automatically. A linter (such as Ruff or Flake8) analyzes code for potential bugs, complexity and style violations. Most teams run both: the formatter for layout, the linter for deeper quality checks.

🔒Is it safe to paste my Python code into an online formatter?

Code is sent to a secure backend over HTTPS and processed transiently for formatting. However, as a best practice you should avoid sending passwords, API keys, personal data or highly confidential business logic to any online tool. For sensitive projects, run Black locally or inside your own CI environment instead.

⚙️Can I integrate this style into my CI pipeline?

Yes. Install Black in your project and run it via pre-commit hooks, GitHub Actions, GitLab CI or any other CI system. This ensures that every branch and pull request is formatted automatically before merge.

🐍Which Python versions are supported by Black-style formatting?

Black is regularly updated for modern Python syntax, including type hints, f-strings, dataclasses and structural pattern matching. Keep both Python and Black up to date to benefit from the latest syntax support.

Pro Tips

Best Practice

Configure your editor (VS Code, PyCharm, Neovim, etc.) to run a Black-style formatter on save so your files are always clean before you commit.

CI Tip

Add Black to pre-commit hooks so every commit is auto-formatted and your repository stays consistent over time.

Security Tip

Avoid sending secrets, credentials or proprietary algorithms to any online formatter. Keep highly sensitive code inside local or CI-based formatting pipelines only.

Best Practice

Combine this formatter with a linter (Ruff, Flake8, pylint): the formatter handles layout, while the linter catches unused imports, complexity and potential bugs.

Best Practice

Align line-length settings across this tool, your local Black configuration and CI so you don’t fight conflicting styles.

Additional Resources

Black: The Uncompromising Python Code Formatter
Documentation
PEP 8 – Style Guide for Python Code
Technical specification
Official Python Tutorial: Coding Style
Reference

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