While reading a book using Python, I learned this for loop else grammar.
The example code is:
# Example searching for prime numbers
>>> for n in range(2, 10):
for x in range(2, n):
if n % x == 0:
print(n, 'equals', x, '*', n//x)
break
else:
# loop fell through without finding a factor
print(n, 'is a prime number')
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3
An else clause is executed when the for loop terminates through exhaustion of the iterable (with for) or when the condition becomes false (with while), but not when the loop is terminated by a break statement.