Summary of the usage of else in the Python loop

  • 2020-05-12 02:46:55
  • OfStack

preface

This article discusses Python for…else and while…else These are the least used and most misunderstood features of Python.

In the Python for , while There's an optional one for each of these loops else Branch (similar to if Statements and try Statement), which is executed after the loop iteration has normally completed. In other words, if we do not exit the loop in any other way than the normal way, then else The branch will be executed. It's not in the circulation break Statement, no return Statement, or no exception occurs.

Let's look at a detailed usage example.

1. Regular use of if else


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

2. if else

Here, while…else0 Can be used as a 3 - bit operator.


mark = 40
is_pass = True if mark >= 50 else False
print "Pass? " + str(is_pass)

3. Use with for keyword 1

In the following cases, else The following code block will be executed:

1. for The statements in the loop are executed

2, for The statements in the loop are not break Statements to interrupt


#  print  `For loop completed the execution`
for i in range(10):
 print i
else:
 print 'For loop completed the execution'
#  Don't print  `For loop completed the execution`
for i in range(10):
 print i
 if i == 5:
 break
else:
 print 'For loop completed the execution'

4. Use with while keyword 1

Similarly, when the following conditions are met, else The following code block will be executed:

1. while The statements in the loop are executed

2, while The statements in the loop are not break Statements to interrupt


#  print  `While loop execution completed`
a = 0
loop = 0
while a <= 10:
 print a
 loop += 1
 a += 1
else:
 print "While loop execution completed"
#  Don't print  `While loop execution completed`
a = 50
loop = 0
while a > 10:
 print a
 if loop == 5:
 break
 a += 1
 loop += 1
else:
 print "While loop execution completed"

5. Use with try except 1

and try except If you don't throw an exception, else The statement can be executed.


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'
 f.close()

conclusion

The usage of else in the loop statement in Python is basically concluded. This article has a definite reference value for you to learn or use Python, and I hope it can be helpful to you. If you have any questions, you can leave a message to communicate.


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