List minimum in Python with None?

Question

Is there any clever in-built function or something that will return 1 for the min() example below? (I bet there is a solid reason for it not to return anything, but in my particular case I need it to disregard None values really bad!)

>>> max([None, 1,2])
2
>>> min([None, 1,2])
>>> 

Spermatic

Answer 1

None is being returned

>>> print min([None, 1,2])
None
>>> None < 1
True

If you want to return 1 you have to filter the None away:

>>> L = [None, 1, 2]
>>> min(x for x in L if x is not None)
1

Evanish

Note that None is only returned in Python 2. In Python 3, min([None, 1, 2]) yields a TypeError: '<' not supported between instances of 'int' and 'NoneType'. – Braeunig

Answer 2

using a generator expression:

>>> min(value for value in [None,1,2] if value is not None)
1

eventually, you may use filter:

>>> min(filter(lambda x: x is not None, [None,1,2]))
1

Keese

The syntax has nothing python 3. It works in python 2 just fine. Using is for comparing with None as in value is not None is prefered to using == (or !=). The line with filter is wrong, try putting a 0 in the list and you'll see it will get filtered too, which is not what you want. – Evanish

Which is quicker, a list comprehension or a filter? – Spermatic

@c00kiemonster: They don't do the same thing. a filter is wrong here, as I pointed in my comment. – Evanish

oh i see, when you said filter in your reply, you meant filter through a list comprehension, and not filter as in filter()... – Spermatic

@nosklo: sorry, i thought generator expressions were introduced in python 3. i already corrected the is not None. and you are right the filter was wrong, corrected now... – Keese

now after the edit, the filter() version got very very ugly... :P – Evanish

@nosklo: i even wrote a worse version: import functools, operator; min(filter(partial(operator.is_not,None),[None,1,2])). with the problem you pointed earlier, there is now nothing to gain using filter(). python is missing a function for testing the common case of being None... – Keese

@Adrien Plisson: Please FIX the first line of your answer; you don't use a list comprehension and as mentioned by nosklo "Python 3 syntax" is irrelevant. – Chlorobenzene

Answer 3

Make None infinite for min():

def noneIsInfinite(value):
    if value is None:
        return float("inf")
    else:
        return value

>>> print min([1,2,None], key=noneIsInfinite)
1

Note: this approach works for python 3 as well.

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