Usage summary of else in Python loop statements _python

Objective

This article discusses the for…else syntax of Python and while…else so on, which is one of the most common and misunderstood grammatical features in Python.

The loops in for python while have an optional else branch (like if statements and try statements) that are executed after the loop iteration is completed normally. In other words, if we are not exiting the loop in any way other than the normal way, then the else branch will be executed. That is, there are no statements in the loop, break no return statements, or no exceptions.

Let's take a look at the detailed usage examples below.

One, the general if else usage

x = True
if x:
 print ' x is True '
else:
 print ' x is not true '

Two, if else quick usage

This if else can be used as a ternary operator.

Mark =
Is_pass = True if Mark >= else False
print "pass?" + str (is_pass)

Third, with the FOR keyword one

The else next code block is executed when the following conditions are true:

1, for the execution of the statement in the loop completes

2, for the statement in the loop is not interrupted by the break statement

# print ' For loop completed the execution ' to
I in range: print
 i
else: print ' for
 Loop completed the ex Ecution '
# do not print ' For loop completed the execution ' to
I in range:
 print i
 if i = 5:
 break
   else:
 print ' For loop completed the execution '

Four, with while keyword one

Similar to the above, the else next code block is executed when the following conditions are true:

1, while the execution of the statement in the loop completes

2, while the statement in the loop is not interrupted by the break statement

# print ' While loop execution completed '
a = 0
loops = 0 while
a <=:
 print a
 loop + = 1
 A + = 1
   else:
 print "While loop execution completed"
# does not print ' while loop execution completed '
a =
loop = 0
   while a >:
 print a
 if loop = = 5:
 break
 A + + 1
 loop + = 1
else:
 print "while loo P Execution Completed "

V. Use with try except

and try except when used together, else the statements in can be executed if the exception is not thrown.

file_name = "Result.txt"
try:
 f = open (file_name, ' R ')
except IOError:
 print ' cannot open ', File_ Name
else:
 # executes only if file opened properly
 print file_name, ' has ', Len (F.readlines ()), ' lines ' C32/>f.close ()

Summarize

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