如何使用Python for和While循环 for循环 (for loop) while循环 (while loop) 结论 (Conclusion)

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编程，Python (Programming, Python)

Do you know Python for and while loops have else statements? Do you know how for and while loops work when used along with else, break, continue & try statements? Read further to understand more about this.

您知道Python for和while循环具有else语句吗？您是否知道for和while循环与else ， break ， continue和try语句一起使用时如何工作？进一步阅读以了解更多信息。

for循环 (for loop)

The general syntax of for loop:

for循环的一般语法：

for val in sequence:

<<body of for loop>>

Let’s look at a couple of simple examples:

让我们看几个简单的例子：

for i in range(3):

print(i)
>> 0
>> 1
>> 2for c in "Hi":

print(c)
>> H
>> i

Now, let’s see how for loop works when else, break, continue, and try statements are used.

现在，让我们看看 使用 else ， break ， continue, 和 try 语句时 for 循环如何工作。

else statement is executed only if the for loop has been terminated normally without encountering break statement.
仅当for循环已正常终止而不遇到break语句时，才执行else语句。
When break statement is encountered, the control comes out of the for loop and execute next statement after the loop
当遇到break语句时，控件从for循环中退出并在循环后执行下一条语句
when continue statement is encountered, it skips the rest of the code inside a loop for the current iteration and continues with next iteration.
当遇到continue语句时，它将在循环中跳过当前迭代的其余代码，并继续进行下一个迭代。
finally statement always executes whether there is an exception or not.
无论是否有异常， finally语句始终执行。

With this understanding of how else, break, continue and try statements work, let us look at the examples of for loop:

了解了else ， break ， continue和try语句如何工作之后，让我们看一下for循环的示例：

Example 1: In this example, the break statement gets executed so control comes out of the for loop without executing else statement.

示例1 ：在此示例中，执行了break语句，因此控制从for循环中出来而无需执行else语句。

Example 2: In this example, since continue statement is used, all the statements are executed including the else statements.

示例2 ：在此示例中，由于使用了continue语句，因此将执行所有语句，包括else语句。

Example 3: In this example, since continue statement is used inside the except statement, all the statements are executed including the else statements. As you can notice, finally statement also gets executed irrespective of exception.

示例3 ：在此示例中，由于在except语句内部使用了continue语句，因此将执行所有语句，包括else语句。如您所见， finally语句也将与异常无关地执行。

Example 4: In this example, ZeroDivisionError exception is caught. Since there is a break statement control comes out of the loop. But as expected finally statement is executed before coming out of the loop.

示例4：在此示例中，将捕获ZeroDivisionError异常。由于存在一个break语句，因此控件退出了循环。但是按预期， finally语句在退出循环之前已执行。

while循环 (while loop)

The general syntax of while loop:

while循环的一般语法：

while test_expression:

<<body of while loop>>

Let’s look at a simple example:

让我们看一个简单的例子：

i = 0
while (i < 3):

print(i)

i+= 1
>> 0
>> 1
>> 2

Now, we can look at the examples for while loop when used with else, break, continue and try statements.

现在，我们可以看看与else ， break ， continue和try语句一起使用时while循环的示例。

Example 1: In this example, since continue statement is used, all the statements are executed including the else statements. Notice that when i==2 the current iteration is skipped.

示例1 ：在此示例中，由于使用了continue语句，因此将执行所有语句，包括else语句。请注意，当i==2将跳过当前迭代。

Example 2: In this example, the break statement gets executed so control comes out of the while loop without executing else statement.

示例2 ：在此示例中，执行了break语句，因此控制权从while循环中出来， while没有执行else语句。

Example 3: In this example, an exception is caught. Since there is a break statement control comes out of the while loop. But as expected finally statement is executed before coming out of the loop.

示例3：在此示例中，捕获了一个异常。由于存在break语句，因此控制从while循环中出来。但是按预期， finally语句在退出循环之前已执行。

Example 4: In this example, since continue statement is used inside the except statement, all the statements are executed including the else statements. As you can notice, finally statement also gets executed irrespective of an exception.

示例4：在此示例中，由于在except语句内部使用了continue语句，因此将执行所有语句，包括else语句。如您所见， finally语句也将与异常无关地执行。