> The idea behind augmented assignment in Python is that it isn’t just an easier way to write the common practice of storing the result of a binary operation in its left-hand operand, but also a way for the left-hand operand in question to know that it should operate on itself, rather than creating a modified copy of itself.
Here's an example of how "a += b" is not syntactic sugar for "a = a + b". First, "a = a + b", which rebinds 'a' to a new object while leaving 'b' bound to the original:
>>> a = b = [9,8]
>>> a + b
[9, 8, 9, 8]
>>> a = a + b
>>> a
[9, 8, 9, 8]
>>> b
[9, 8]
>>> a = b = [9,8]
>>> a += b
>>> a
[9, 8, 9, 8]
>>> b
[9, 8, 9, 8]It was meant to show your comment at https://news.ycombinator.com/item?id=32741165 wasn't a relevant parallel, because it ignored how "a+=1" and "a=a+1" are different.
For a more convincing use, consider NumPy arrays, where a+=1 re-use the same (potentially very large) array, while a=a+1 creates a new array.
import numpy
a = b = numpy.array([[1,2], [3, 9]])
a += 1 # modify in-place
a = a + 1 # create a new array
>>> a
array([[ 3, 4],
[ 5, 11]])
>>> b
array([[ 2, 3],
[ 4, 10]])
> The solution to "Python needs a way to increment variables" is usually to so `a = a + 1`.
> To make this proposal convincing, we need a realistic example of an algorithm that uses it, and that example needs to be significantly more readable and maintainable than `a = a + 1`.
Why does `+=` get into the language but labelled breaks (a reasonably standard feature) don't. This isn't hypothetical - not all languages have +=. Matlab for example requires you to do `a = a + 1`.