CODEWITHSUNDEEP
python
Lokty
Lokty

Reputation: 95

Conditional inside int(x) method even though it doesn't take Boolean values

I am studying the Python built-in method int(x), which casts a variable to int. The documentation is at https://docs.python.org/2/library/functions.html#int.

In a code I found:

errors += int(update != 0.0)

This code simply increases or decreases an error variable. What i see is a conditional as a variable, even though the method doesn't take Boolean values. How is this possible?

Upvotes: 1

Views: 132

Answers (3)

Ry-
Ry-

Reputation: 225074

The Python 3 documentation is ever so slightly more straightforward than the 2 documentation here, so I’ll quote it:

Return an integer object constructed from a number or string x, or return 0 if no arguments are given. If x is a number, return x.__int__().

So int accepts a string or a number. Booleans aren’t strings, but they are in fact numbers! Following the link to Numeric Types – int, float, complex explains that…

There are three distinct numeric types: integers, floating point numbers, and complex numbers. In addition, Booleans are a subtype of integers.

which you can confirm in the REPL:

>>> import numbers
>>> isinstance(False, int)
True
>>> isinstance(True, numbers.Numeric)
True

and by doing math with booleans, which act as the integer values 0 and 1 as one would expect:

>>> True * 5
5
>>> math.acos(False)
1.5707963267948966

Upvotes: 2

Muku
Muku

Reputation: 562

Booleans are a sub class of Integers in python and internally and False is represented as 0 in Python.

Upvotes: 0

taesu
taesu

Reputation: 4580

Consider two possibilities:

int(True) and int(False)
First case will evaluate to 1 and second to 0
hence, errors will either increase by 1 or by 0

refer to the doc

Boolean values are the two constant objects False and True. They are used to represent truth values (although other values can also be considered false or true). In numeric contexts (for example when used as the argument to an arithmetic operator), they behave like the integers 0 and 1, respectively. The built-in function bool() can be used to convert any value to a Boolean, if the value can be interpreted as a truth value (see section Truth Value Testing above).

Upvotes: 2

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