LambdaType vs FunctionType

See cpython/Lib/types.py:

def _f(): pass
FunctionType = type(_f)
LambdaType = type(lambda: None)         # Same as FunctionType

Back in 1994 I wasn't sure that we would always be using the same implementation type for lambda and def. That's all there is to it. It would be a pain to remove it, so we're just leaving it (it's only one line). If you want to add a note to the docs, feel free to submit a PR.