How to convert float to integer strictly, without rounding?

Question

I wish to find a way to achieve the following: With the likes of 5.0, return 5. With the likes of 5.1, which cannot equal any integer, return Error.

Currently I use int() together with an "if integer != float". However this has problems, for instance I won't be able to tell whether the inequality was caused by the likes of 5.1 or the likes of 1111111111111111.0(and even larger numbers).

Also this is extremely troublesome compared with a potential, simple, one-line command. So is there a command in Python that does this?

Answer 1

Float objects in Python have an is_integer() predicate.

def strict_int(x):
    if x.is_integer():
        return int(x)
    raise ValueError

Note that int objects do not have this method. You'll get an attribute error if you try to call this on an int.

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If you wanted some error value instead of an exception, you can use a one-liner like this

int(x) if x.is_integer() else 'Error'