What's the difference?

Python Help
1

1 variant

dig = int(input())
a = 1
while dig > 0:
    a = a * dig % 10
    dig = dig // 10
print(a)
  1. 2 variant
dig = int(input())
a = 1
while dig > 0:
    a *= dig % 10
    dig = dig // 10
print(a)

What’s the difference? why is the code executed differently, even though the syntax is the same
dig = 415
first variant answer 0
second variant answer 20

CPython versions tested on:

3.12

Operating systems tested on:

Windows

2

a = a * dig % 10 is a = (a * dig) % 10.

a *= dig % 10 is a = a * (dig % 10).

2 Likes
3

oh… i dont know it. thank you very much
it turns out, that last loop a*5 = 20 and 20 % 10 = 0. oh… is so interesting.
Is this not a syntaxis sugar?

4

The *= operator (and its friends +=, -=, /=, etc.) are called augmented assignments, which is a type of syntactic sugar, yes. You still need to be careful with operator precedence. For all augmented assignments, the precedence is:

# These are equivalent:
a += x
a = a + (x)

# As are these:
a *= x
a = a * (x)

where x can be a single variable or an expression, as in your case.

2 Likes
5

Quibble: your equivalences aren’t quite the same in some edge cases.

t = [], 2, 3
t[0] = t[0] + [1]  # raises a TypeError, t[0] is unchanged
t[0] += [1]        # raises a TypeError, but t[0] becomes [1]
1 Like
6

I understood
Thank you very much