Summary of usage of else in Python loop statements

Preface

This article discusses Python’sfor…elseandwhile…elsesyntax. These are the most popular syntaxes in Python. One of the least commonly used and most misunderstood features of grammar.

for,whileand other loops in Python have an optionalelsebranch (similar to theifstatement Like thetrystatement), it is executed after the loop iteration has completed normally. In other words, if we don't exit the loop any other way than the normal way, theelsebranch will be executed. That is, there is nobreakstatement, noreturnstatement, or no exception occurs in the loop body.

Let’s take a look at detailed usage examples.

1. Conventional if else usage

##

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

2. If else shortcut usage

if elsehere can be used as a ternary operator.

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

3. Use it with the for keyword

elsewill be executed:

forloop are executed

forThe statements in the loop are not interrupted by thebreakstatement

# 打印 `For loop completed the execution` for i in range(10): print i else: print 'For loop completed the execution' # 不打印 `For loop completed the execution` for i in range(10): print i if i == 5: break else: print 'For loop completed the execution'

## 4. Usewith the while keyword. Similar to the above, when the following conditions are met, the code block under

will be executed:1.

The statements in the loop are executed
2.

The statements in the loop are not interrupted by thebreakstatement Break

# 打印 `While loop execution completed` a = 0 loop = 0 while a <= 10: print a loop += 1 a += 1 else: print "While loop execution completed" # 不打印 `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. Useand # together with try except ##try except

elsecan 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()

This is a summary of the usage of else in loop statements in Python That’s basically it. This article still has certain reference value for everyone to learn or use Python. I hope it can be helpful to everyone. If you have any questions, you can leave a message to communicate.