Expansion of the `yield from` statement, from PEP 380 -- Syntax for Delegating to a Subgenerator

yield_from_expansion.py

# Code below is the expansion of the statement:
#
# RESULT = yield from EXPR
#
# Copied verbatim from the Formal Semantics section of
# PEP 380 -- Syntax for Delegating to a Subgenerator
#
# https://www.python.org/dev/peps/pep-0380/#formal-semantics

_i = iter(EXPR)
try:
    _y = next(_i)
except StopIteration as _e:
    _r = _e.value
else:
    while 1:
        try:
            _s = yield _y
        except GeneratorExit as _e:
            try:
                _m = _i.close
            except AttributeError:
                pass
            else:
                _m()
            raise _e
        except BaseException as _e:
            _x = sys.exc_info()
            try:
                _m = _i.throw
            except AttributeError:
                raise _e
            else:
                try:
                    _y = _m(*_x)
                except StopIteration as _e:
                    _r = _e.value
                    break
        else:
            try:
                if _s is None:
                    _y = next(_i)
                else:
                    _y = _i.send(_s)
            except StopIteration as _e:
                _r = _e.value
                break
RESULT = _r