About the Python Compiler

The Python Compiler runs Python 3 in your browser with Pyodide, a WebAssembly build of CPython that includes the standard library. Programs can read standard input, and your code never leaves your device.

Your code runs in an isolated Web Worker in your browser, so it never leaves your device.

How to use the Python Compiler

1. Write or paste Python code.
2. Add input lines in the stdin box for input().
3. Click Run. The first run downloads the Python runtime (about 10 MB); later runs start instantly.

Example

name = input()
print(f"Hello, {name}!")
print(sum(range(1, 11)))

Hello, Ada!
55

Common mistakes

• input() with an empty stdin box. There is no interactive prompt. Put every value your program reads into the stdin box, one per line, before you click Run. With nothing left to read, input() returns an empty string (so int(input()) raises ValueError) and the next call raises EOFError.
• Third-party packages. import requests or import numpy fails because only the standard library is available. Use urllib, json, csv, statistics and the other built-in modules.
• Network and files. The program runs in a browser sandbox, so it cannot open sockets or read files on your computer. Paste the data into the code or stdin instead.

Works well with the Python Compiler

• JSON Formatter: pretty print JSON your program outputs.
• JavaScript Compiler: compare the same logic in JavaScript.
• Text & Code Diff: compare actual output with the expected output.

Frequently asked questions

Guides and tutorials

• Programming Languages

  How to Run Python Code Online (No Install, With Input)

  Run Python code online in your browser: a first program, input() and stdin, reading many lines, which modules work, and how to read a Python traceback.

  October 28, 2026 · 5 min read

• Programming Languages

  How to Run R Code Online (No RStudio, No Install)

  Run R code online in your browser without RStudio: print values, explore built-in datasets, fit a linear model, read stdin, and fix the most common R errors.

  October 28, 2026 · 5 min read

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