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Known Limitations

PyRust is a minimal educational interpreter. The following features are not yet implemented or are intentionally out of scope.

Language features

  • No comprehensions or generator expressions — list/dict/set comprehensions and (x for x in ...) are not parsed
  • No async/await, yield, yield from — coroutines and generators are not supported
  • No match / case — structural pattern matching (PEP 634) is not implemented
  • No annotated assignment — x: int = 1 is not parsed
  • print file argument — file= accepts None only; real stream redirection is not supported
  • Assigned names are function-local — a name assigned anywhere in a function body is treated as local for the entire function, matching CPython's scoping rule, but UnboundLocalError is not always raised in the same places

Function signatures

  • No positional-only parameters — the / separator in def f(a, /, b) is not supported
  • No annotations with runtime meaning — parameter and return annotations are ignored

Classes and object model

  • Single inheritance only — multiple base classes are not supported
  • No super()
  • No classmethod, staticmethod, property — descriptor protocol is not implemented
  • No __getattr__, __getattribute__, __setattr__, __delattr__ — attribute hooks are not invoked
  • No __call__, __iter__, __next__, __len__, __bool__ — most dunder methods are not dispatched (exceptions: __init__, @/@=)
  • No __dict__, __class__ — instance and class namespace inspection is not supported

Built-in types

  • set has no methods — set literals work, but add, remove, union, intersection, etc. are not implemented
  • No frozenset, complex, bytes, bytearray — these types are not available
  • Strings — the following str methods are not implemented: casefold, center, ljust, rjust, zfill, expandtabs, encode, format, format_map, maketrans, translate, partition, rpartition, splitlines, removeprefix, removesuffix, swapcase, title, islower, isupper, istitle, isascii, isdecimal, isnumeric, isidentifier, isprintable
  • String literal forms — bytes (b"..."), raw (r"..."), triple-quoted, and f-strings are not supported

Built-in functions

Not yet implemented: all, any, repr, callable, delattr, format, map, filter, iter, next, issubclass, hash, chr, ord, bin, oct, hex, round, divmod, pow, frozenset, complex, bytearray, bytes, globals, locals, vars, ascii, input, open

math module

Not yet implemented: tau, degrees, radians, sinh, cosh, tanh, acosh, asinh, atanh, gcd, lcm, factorial, comb, perm, isqrt, trunc, fmod, modf, remainder, fsum, hypot, dist, isclose, isfinite, copysign, cbrt, exp2, expm1, log1p, erf, erfc, gamma, lgamma

Imports and modules

  • Relative imports — from . import x is not supported
  • Standard library — only math and sys are available as built-in modules

Error reporting

  • No tracebacks — exceptions show an error message but no Python-style stack trace
  • Incomplete exception hierarchy — only the classes listed in features.md are available; OSError, AttributeError, NameError, etc. are raised as RuntimeError internally

REPL

  • Single-line input only — compound statements (functions, classes, if, for, etc.) must be run as a script file