5 Times Python Made Me Say WTF

Learn some funny Python oddities

Python is a popular programming language. As with any other great programming language, Python sometimes makes the developers scratch their heads.

Today I will show you five “funny” WTFs in Python. And no, I’m not talking about bugs.

1. Sometimes Two Equal Numbers Aren’t Equal

Let’s use Python’s is operator to compare two equal numbers and see what happens:

>>> a = 256
>>> b = 256
>>> a is b
True
>>> a = 257
>>> b = 257
>>> a is b
False

How does it work

First of all, the == operator is used to check if two variables are equal. The is operator, on the other hand, checks if the variables point to the same object.

Secondly, Python does some optimization under the hood. Some commonly used objects, e.g., small numbers (between -5 and 256) are allocated only once. But larger numbers are allocated on-demand as many times as needed.

Here’s an example:

>>> x = 1000
>>> y = 1000
>>> z = 1000

The number 1000 is allocated three times, so even though the numbers x,y, and z are equal, they all have a different 1000 assigned to them. However, here is another example:

>>> a = 255
>>> b = 255
>>> c = 255

The number 255 has been allocated only once, so the “same 255” is used three times. And this is actually what the is operator is interested in, rather than the values being equal.

There is always only one 255 but there can be multiple 1000s for example. Image credit: Author.

The key takeaway: Don’t use is to compare numbers, even though it sometimes works.

2. It Is What It Isn’t

>>> 'something' is not None
True
>>> 'something' is (not None)
False

How does it work

• is not is actually a single binary operator. Thus, it has behavior different than using is and not separately.
• is not returns False if the compared variables…