cast¶

basedpython adds a cast infix soft keyword for inline type casts:

b = a cast int

by default this is a checked cast — it verifies the value at runtime and raises on a mismatch — so it transpiles to:

def _checked_cast(_v, _t):
    if not isinstance(_v, _t):
        raise TypeError(
            f"cast to {getattr(_t, '__name__', _t)} failed: value is {type(_v).__name__}"
        )
    return _v

b = _checked_cast(a, int)

see checked cast for the runtime semantics, the safe cast? variant, and the --no-checked-cast flag (which degrades cast to an unchecked typing.cast).

syntax¶

cast is an infix soft keyword: <value> cast <type>. the left operand is the value being cast, the right operand is the target type

b = a cast int | str             # checked cast to int | str
f(a cast int)                    # f(a checked-cast to int)

the inferred type is the target type (b is int), so the checker narrows exactly as typing.cast would.

scope¶

cast is a basedpython-only keyword: a .py file using it as an infix produces a parse error. when the next token cannot start an expression (e.g. cast = 5 or cast(int, a)), cast is parsed as an ordinary identifier so existing python code that uses cast as a name or function call continues to parse