What is the use of "else" after "for" loop in Python?

Question

It seems both of the below codes are printing the same, then what is the need of "else" block after "for" loop in python.

Code 1:

for i in range(10):
    print i
else:
    print "after for loop"

Code 2:

for i in range(10):
    print i

print "after for loop"

Thanks in advance.

score 5 · Accepted Answer · answered May 13 '14 at 07:33

From the documentation:

Loop statements may have an else clause; it is executed when the loop terminates through exhaustion of the list (with for) or when the condition becomes false (with while), but not when the loop is terminated by a break statement.

Follow the link for an example how this can be used.

Dmitry Bychenko · Answer 2 · 2014-05-13T07:39:11.220

4

else executes after for providing for wasn't terminated with break:

 for i in range(10):
    print i

    if (i == 8):
        break # termination, no else    
 else:
    print "after for loop"

edited May 13 '14 at 07:39

answered May 13 '14 at 07:33

Dmitry Bychenko

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1

What happens when the range is empty (i.e. when the loop body isn't executed at all)? – Aaron Digulla May 13 '14 at 07:35
1

@AaronDigulla Then the `break` cannot be reached. So the loop acts as if there was no `break, `going to `else`. – glglgl May 13 '14 at 07:37
@Aaron Digulla: "else" will be executed since "for" is not interrupted – Dmitry Bychenko May 13 '14 at 07:38

Reblochon Masque · Answer 3 · 2014-05-13T08:24:16.730

This was originally enacted in order to get rid of all the "GOTO" statements in procedures without using flags: It means "NO BREAK"

for i, value in enumerate(sequence):
    if value == target:
    break
else:           #<-- if we finish the loop and did not encounter break, return -1
    return -1
return 1        #<-- if we did encounter break, return 1

You can watch Raymond Hettinger's Pycon talk that mentions the for/else construct here: Transforming Code into Beautiful, Idiomatic Python, http://pyvideo.org/video/1780/transforming-code-into-beautiful-idiomatic-pytho

What is the use of "else" after "for" loop in Python?

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