Run Python code directly in the browser via Pyodide WebAssembly with standard library support.
This playground runs real CPython inside your browser tab. The interpreter is compiled to WebAssembly by Pyodide, so scripts execute locally with the full standard library and no server involvement: the code you type never leaves your machine. The most common surprise is startup - the first run downloads a multi-megabyte WASM runtime, so output can lag several seconds behind your click. It is a full interpreter, not a calculator: define functions, import modules, and run multi-line programs, and the page keeps one interpreter session alive, so names from an earlier run can affect the next.
A concrete input and expected output from the current implementation.
Input
def fib(n):
a, b = 0, 1
for _ in range(n):
a, b = b, a + b
return a
print([fib(i) for i in range(10)]) Expected output
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
The playground executes this as a complete program: fib is defined, the comprehension calls it for 0 through 9, and print writes the resulting list. The values follow the Fibonacci recurrence, so fib(0)=0, fib(1)=1, and each later term is the sum of the two before it.
The page loads Pyodide, a build of CPython compiled to WebAssembly, into your tab. When you press Run, the interpreter executes your code and print() output is captured into the results pane. Imports resolve against the standard library bundled with the WASM build, and Pyodide-built packages such as numpy, pandas, and matplotlib are usable without installing anything.
The interpreter instance stays alive for the life of the page, so a later run typically sees variables and functions defined by an earlier run; reloading the page wipes everything and starts fresh. The first run is the slow one, because the several-megabyte WASM runtime must download and instantiate before any output can appear. Subsequent runs start in a fraction of that time.
No. Pyodide executes the code inside your browser tab; there is no server-side interpreter and nothing you type or run is uploaded. The only network traffic is the download of the WASM runtime and any package wheels when they are first needed, which you can verify in the browser's network panel.
Only in a limited sense. Pyodide ships a curated set of packages compiled for WebAssembly, including numpy, pandas, and matplotlib. A package with C extensions works here only if a WASM build exists for it; many packages you could pip install locally will fail, so check the bundled package list before relying on one.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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