multiline-lambda-hack.py

import re


def inline_func(code: str, globals_=None, locals_=None):
    if globals_ is None: globals_ = globals()
    if locals_ is None: locals_ = locals()

    lines = code.splitlines(keepends=True)
    indent = None
    func_name = None
    for i, line in enumerate(lines):
        if indent is None:
            if m := re.match(r'^(\s*)def\s+(\w+)', line):
                indent, func_name = m.groups()
                lines[i] = line.replace(indent, '', 1)
        else:
            lines[i] = line.replace(indent, '', 1)

    code = ''.join(lines).strip()
    exec(code, globals_, locals_)
    return locals_[func_name]


assert list(map(inline_func(
    '''
    def f(x):
        return (x + 1) ** 2
    '''
    ),
    range(3)
)) == [1, 4, 9]