Python Online Compiler

About this tool

Python Online Compiler lets you write and run Python 3 code directly in your browser, powered by Pyodide — a full CPython 3.11 runtime compiled to WebAssembly. There is nothing to install and no account required. Your code never leaves your machine; everything executes locally in the browser tab. On first use, Pyodide downloads around 10 MB and is cached by the browser, making subsequent runs instant. Standard library modules work as expected, and you can install third-party packages like NumPy, Pandas, Matplotlib, and Requests using micropip inside your script. Standard output and standard error are captured and displayed in a colour-coded output panel. The editor supports Tab-key indentation. This tool is ideal for learners, educators, interviewers, and developers who need to test a Python snippet without leaving the browser.

Why use it

• Zero install — runs CPython 3.11 in WebAssembly, no server required

• Private by default — code and data never leave your browser tab

• Third-party packages available via micropip (NumPy, Pandas, and more)

• Fast after first load — Pyodide is cached by the browser

• Works on any modern desktop or mobile browser

• Zero install — runs CPython 3.11 in WebAssembly with no server, no Docker, no virtualenv setup

How to use

1. Type or paste Python 3 code into the editor — Tab inserts spaces, Shift-Tab dedents.
2. Click Run — Pyodide loads on first use (approx 10 MB, then cached by your browser for instant restarts).
3. Standard output and errors appear in the Output panel below.
4. Load the package installer first: import pyodide_js; await pyodide_js.loadPackage('micropip'). Then import micropip and use await micropip.install('packagename').
5. Click Clear Output to reset the panel without losing your code.

When it helps

• Testing a quick Python snippet without opening a terminal or activating a virtualenv
• Learning Python or following along with a tutorial
• Technical interviews where a shareable Python environment is needed
• Prototyping data transformation logic before adding it to a project
• Teaching Python in a classroom with no local setup

Examples

for i in range(1, 16):
    if i % 15 == 0: print('FizzBuzz')
    elif i % 3 == 0: print('Fizz')
    elif i % 5 == 0: print('Buzz')
    else: print(i)

1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz

import json
data = '[{"city":"NYC","pop":8.3},{"city":"LA","pop":3.9}]'
rows = json.loads(data)
total = sum(r['pop'] for r in rows)
print(f'Total population: {total:.1f}M')

Total population: 12.2M

import pyodide_js
await pyodide_js.loadPackage('numpy')
import numpy as np
arr = np.array([10, 20, 30, 40, 50])
print('Mean:', arr.mean(), 'Std:', arr.std().round(2))

Mean: 30.0 Std: 14.14

Tips

• Top-level await works in this editor. To load a bundled package, import pyodide_js and call await pyodide_js.loadPackage('numpy') before importing it.
• Pre-bundled scientific packages (numpy, pandas, scipy) install much faster than pure-Python wheels from PyPI.
• For PyPI packages, first load micropip with await pyodide_js.loadPackage('micropip') after importing pyodide_js. Then import micropip and use await micropip.install('package==version') to pin a version.
• The console updates when a run finishes. Split a long computation into smaller runs when you need to inspect intermediate results.
• Avoid deeply recursive code — WebAssembly stack limits are tighter than CPython's default 1000-frame limit.
• For large inputs, paste data into a triple-quoted string rather than reading from a file — there is no host filesystem.
• Use json.dumps(obj, indent=2) for readable output when inspecting nested dicts or API response shapes.

Frequently Asked Questions

Glossary

Pyodide

A port of CPython 3.11 to WebAssembly maintained by the Python community, enabling Python execution inside a browser tab without a server.

WASM (WebAssembly)

A portable binary instruction format that runs in browsers at near-native speed and is sandboxed from the host system.

Micropip

Pyodide's lightweight package installer that loads pure-Python wheels from PyPI or pre-built scientific packages from the Pyodide CDN.

REPL

Read-Eval-Print Loop — an interactive shell where each expression is immediately evaluated and printed; this tool acts as a script-style REPL.

Sandboxed worker

A Web Worker isolated from the main page's DOM, cookies, and storage, used to safely run untrusted code like user Python scripts.

AST (Abstract Syntax Tree)

A tree representation of Python source code that the interpreter builds before execution; you can inspect it via the ast module.

Wheel (.whl)

A pre-built binary distribution format for Python packages; micropip installs wheels rather than building from source.

Standard library

Modules shipped with CPython itself (json, re, math, etc.) that work in Pyodide without any package install.