What does //= in python do? [duplicate]

Answer 1

// is floor division: it divides and rounds down, though it still produces a float if the operands are floats. In Python 2, it's the same as regular division for integers, unless you use from __future__ import division to get Python 3's "true" division behavior.

So, yes, this is a little complicated. Essentially it exists to recreate the behavior you get in Python 2 by dividing two integers, because that changes in Python 3.

In Python 2:

• 11 / 5 → 2
• 11.0 / 5.0 → 2.2
• 11 // 5 → 2
• 11.0 // 5.0 → 2.0

In Python 3, or Python 2 with from __future__ import division, or Python 2 run with -Q new:

• 11 / 5 → 2.2
• 11.0 / 5.0 → 2.2
• 11 // 5 → 2
• 11.0 // 5.0 → 2.0

And, of course, adding the = just turns it into a combo assignment operator like /=.