Austin Henley builds a Python interpreter in 1024 bytes of C
Original: Making a Python interpreter in 1024 bytes
Why This Matters
Illustrates the minimal computational footprint required to implement a recognizable scripting language runtime.
Microsoft researcher Austin Z. Henley built a minimal Python interpreter in 1024 bytes of C code, with no macros or libraries. The interpreter supports FizzBuzz-style Python programs, including def, for/range, if/else, indentation, and single-character variable names.
Austin Z. Henley, a researcher at Microsoft, shared a weekend coding challenge: writing a Python interpreter in just 1024 bytes of pure C — no macros, no library calls. An initial attempt targeting 512 bytes proved insufficient, so the limit was relaxed to 1024.
The interpreter supports a recognizable Python subset: def, for n in range(N), if/else with colons and indentation, print(), and basic arithmetic. Variable names are restricted to single lowercase characters, enabling direct array-indexed symbol table lookups (vars[ch]).
Rather than tokenizing into an AST and emitting bytecode like CPython, the interpreter uses a handful of global variables — a fixed 999-character source buffer, a 256-entry integer variable table, and position/character pointers. Expressions are evaluated via a classic recursive descent parser that executes inline. There is no error handling; the interpreter assumes well-formed input.
Control flow is managed by tracking indentation levels: a run_block() function executes lines until indentation decreases, using the C call stack for nesting. Loops are handled by recording source positions and replaying them. The project, published September 6, 2026, demonstrates the lower bounds of a functionally recognizable Python implementation.