Simple inline codegen. Generate things like typing overloads in-file by running the file.

example.py

from typing import overload, Any

# <gen_get_overloads codegen>
# Anything in here is replaced with the result of gen_get_overloads()
# </gen_get_overloads>

def get(val: Any) -> Any:
    return val

if __name__ == "__main__":
    import re, textwrap

    def gen_get_overloads():
        return "\n\n".join(
            f"@overload\ndef get(val: {typ}) -> {typ}:\n    ..."
            for typ in ("str", "int", "bool")
        )

    with open(__file__, "r") as h:
        code = h.read()

    newcode, n = re.subn(
        r"(?ms)((^[ \t]*)# *<([^ ]+) +codegen>[ \t]*$).*?(^[ \t]*# *</\3>[ \t]*$)",
        lambda m, g=globals(): f"{m.group(1)}\n{textwrap.indent(g[m.group(3)](), m.group(2))}\n{m.group(4)}",
        code,
    )

    if newcode != code:
        compile(newcode, __file__, "exec") # Sanity check the syntax is still valid
        with open(__file__ + ".codegen.bak", "w") as h: h.write(code)
        with open(__file__, "w") as h: h.write(newcode)
        print(f"Updated {n} codegen blocks!")