types - How can I check if my python object is a number?

243
votes

In Java the numeric types all descend from Number so I would use

(x instanceof Number).

What is the python equivalent?

5
pythontypesnumbers
Not really a duplicate, the other one is a very specific case of this question (check if something is a number in a vector), and most voted answers really relate to that detail. - jb.
Multiply x by zero. if the results is anything other than zero then x is not a number see: stackoverflow.com/a/44418960/3419693 - shrewmouse

5 Answers

298
votes

Test if your variable is an instance of numbers.Number:

>>> import numbers
>>> import decimal
>>> [isinstance(x, numbers.Number) for x in (0, 0.0, 0j, decimal.Decimal(0))]
[True, True, True, True]

This uses ABCs and will work for all built-in number-like classes, and also for all third-party classes if they are worth their salt (registered as subclasses of the Number ABC).

However, in many cases you shouldn't worry about checking types manually - Python is duck typed and mixing somewhat compatible types usually works, yet it will barf an error message when some operation doesn't make sense (4 - "1"), so manually checking this is rarely really needed. It's just a bonus. You can add it when finishing a module to avoid pestering others with implementation details.

This works starting with Python 2.6. On older versions you're pretty much limited to checking for a few hardcoded types.

203
votes

Python 3:

isinstance(x, (int, float, complex)) and not isinstance(x, bool)

Python 2:

isinstance(x, (int, long, float, complex)) and not isinstance(x, bool)

Note that this answer works incorrectly for Numpy objects.

56
votes

Use Number from the numbers module to test isinstance(n, Number) (available since 2.6).

isinstance(n, numbers.Number)

Here it is in action with various kinds of numbers and one non-number:

>>> from numbers import Number
... from decimal import Decimal
... from fractions import Fraction
... for n in [2, 2.0, Decimal('2.0'), complex(2,0), Fraction(2,1), '2']:
...     print '%15s %s' % (n.__repr__(), isinstance(n, Number))
              2 True
            2.0 True
 Decimal('2.0') True
         (2+0j) True
 Fraction(2, 1) True
            '2' False

This is, of course, contrary to duck typing. If you are more concerned about how an object acts rather than what it is, perform your operations as if you have a number and use exceptions to tell you otherwise.

1
votes

Sure you can use isinstance, but be aware that this is not how Python works. Python is a duck typed language. You should not explicitly check your types. A TypeError will be raised if the incorrect type was passed.

So just assume it is an int. Don't bother checking.

-5
votes

That's not really how python works. Just use it like you would a number, and if someone passes you something that's not a number, fail. It's the programmer's responsibility to pass in the correct types.