Python for…else construct
As documented in the for loop syntax thefor loop allows an else block, and so does the while loop, so that you can write something like:
r = range( 2 )
for i in r:
print( f"Looping {i}" )
else:
print( "Else block" )
r = None
while r is not None:
print( f"While {r}" )
r -= 1
if r == 0:
r = None
else:
print( "While else block" )
The idea is quite interesting, after all, even if I don’t like how it is implemented. As stated in the documentation, the
else block is executed when the iterator is exhausted, hence when the looping ends (or it never starts).
Therefore, in the first for example, the else block is executed once the iteration ends, and in the while it is immediatly executed since the iterator is empty (and an empty iterator is seens as an exhausted one).
The usage of an else block simplifies the code because you don’t need anymore an if to check if your iterator is empty or not. The problem is that the else block is executed even if the iterator was full!
I was expecting something like:
r = range( 2 )
if r is not None:
for i in r:
...
else:
print( "Iterator empty" )
while effectively it is implemented as it was written as:
r = range( 2 )
done = False
for i in r:
...
done = True
if not done or r is None:
print( "Iterator is empty" )
that makes much less value according to me.