What is the usage of else in Python loop structure?

Loop structures in Python include for loops and while loops. These loop structures can help the program repeatedly execute a block of code until a specific condition is met. In addition to the loop itself, Python also provides a special keyword else for executing a specific piece of code after the loop ends. This article will introduce in detail the usage of else in Python loop structure.

In Python, the syntax of the loop structure is as follows:

1. for loop:

for variable in sequence:

# 循环体
else:
# 循环结束后执行的代码

2. while loop:

while 条件:
# 循环体
else:
# 循环结束后执行的代码

In the above syntax, the else block is optional and you can choose whether to use it according to your needs.

When the loop ends normally, that is, when the loop condition is no longer met, the code in the else block will be executed. This means that if the loop is not interrupted by a break statement, then the code in the else block will be executed.

The following uses some examples to illustrate the usage of else in loop structures.

Example 1: for loop

for i in range(5):

print(i)
else:
print("循环结束")

Output result:

0
1
2
3
4
循环结束

In this example, the for loop is normal It is executed 5 times, so the code in the else block is executed.

Example 2: Using break in a for loop

for i in range(5):
if i == 3:
break
print(i)
else:
print("循环结束")

Output result:

0
1
2

In this example, when i equals 3, the break statement is used to interrupt the loop, Therefore the code in the else block will not be executed.

Example 3: while loop

i = 0
while i < 5:
print(i)
i += 1
else:
print("循环结束")

Output result:

0
1
2
3
4
循环结束

In this example, the while loop is executed normally 5 times, so the code in the else block is executed.

Example 4: Using break in the while loop

i = 0
while i < 5:
if i == 3:
break
print(i)
i += 1
else:
print("循环结束")

Output result:

0
1
2

In this example, when i equals 3, the break statement is used to interrupt the loop, Therefore the code in the else block will not be executed.

Summary:

In Python’s loop structure, the else block is used to execute a specific piece of code when the loop ends normally. If the loop is interrupted by a break statement, the code in the else block will not be executed. Using else blocks can make the code clearer and easier to understand, and can perform some necessary operations after the loop ends. .

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