问题
This is possible in python2:
None < float('-inf')
Also, it always returns
True
However, on python3, this throws
TypeError: unorderable types: NoneType() < int()
Why is None comparable to integers/floats with python2? Are there any benefits or applications to None being orderable in python2?
回答1:
First of all Python 2 allowed comparing all types of mixed types. This wart was fixed in Python 3 eventually.
CPython implementation detail: Objects of different types except numbers are ordered by their type names; objects of the same types that don’t support proper comparison are ordered by their address.
For None a quick decision was made by Guido and Tim Peters and it resulted in this commit in Python 2.1(emphasis mine):
Part of fixing that was removing some cases of "compare objects of different types by comparing the type name strings". Guido & I were both in the office at the time, and one said to the other: "what about
None? Comparing that to other types via comparing the string'None'doesn't make much sense." "Ya, OK ... how about changingNoneto - by default - comparing 'less than' objects of other types?" "Don't see why not - sure." "OK, done!No more than 2 minutes of thought went into it. There was no intent to cater to any real use case here - the only intent was to pick some arbitrary-but-consistent rule that didn't suck quite as badly as pretending None was the string "None" ;-)
来源：https://stackoverflow.com/questions/45449718/a-number-smaller-than-negative-infinity-in-python