Python For Loops

Python For Loops

In this article, we will delve into the topic of Python for loops. A for loop is an important construct in Python, which is used to execute a block of code repeatedly. It is widely used in Python programming, and therefore, it is essential to have a good understanding of it. （在本文中，我们将深入探讨Python for循环的主题。for循环是Python中的一个重要构造，用于重复执行代码块。它在Python编程中被广泛使用，因此，对它有一个很好的理解是必不可少的。）

What is a for loop? #

What is a for loop? （什么是for循环？）

A for loop is a type of loop that is used to iterate over a sequence. The sequence can be a list, tuple, set, dictionary, or any other iterable object. The basic syntax of a for loop is:

for item in sequence:
   # do something with item

Here, item is a variable that takes on each value in the sequence, one by one. The block of code inside the loop is executed once for each value of item. （这里， item是一个变量，逐个接受序列中的每个值。循环内的代码块对项目的每个值执行一次。）

Example of a for loop #

Example of a for loop （For循环示例）

Let’s take a simple example to understand how a for loop works:

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
   print(fruit)

Output:

apple
banana
cherry

Here, we have a list of fruits. We use a for loop to iterate over the list, and print each fruit on a new line. （在这里，我们有一份水果清单。我们使用for循环对列表进行迭代，并将每个水果打印在新行上。）

Range function #

Range function （RANGE函数）

The range() function is commonly used in for loops. It generates a sequence of numbers, which can be used as the sequence in a for loop. The syntax of the range() function is:

range(start, stop, step)

Here, start is the starting number of the sequence (default is 0), stop is the ending number of the sequence (not included), and step is the step size (default is 1). （这里， start是序列的起始编号（默认值为0 ） ， stop是序列的结束编号（不包括） ， step是步长（默认值为1 ）。）

Example of range function in a for loop #

Example of range function in a for loop （For循环中的range函数示例）

Let’s take an example to see how the range() function can be used in a for loop:

for i in range(1, 6):
   print(i)

Output:

1
2
3
4
5

Here, we use the range() function to generate a sequence of numbers from 1 to 5. We then use a for loop to iterate over the sequence and print each number on a new line. （在这里，我们使用range ()函数生成从1到5的数字序列。然后，我们使用for循环对序列进行迭代，并在新行上打印每个数字。）

Nested for loops #

Nested for loops （嵌套循环）

A for loop can also be nested inside another for loop. This is useful when we need to iterate over multiple sequences simultaneously. The syntax for a nested for loop is:

for item1 in sequence1:
   for item2 in sequence2:
       # do something with item1 and item2

Here, the inner for loop is executed once for each value of the outer for loop. （这里，内部for循环对外部for循环的每个值执行一次。）

Example of nested for loop #

Example of nested for loop （嵌套for循环的示例）

Let’s take an example to see how a nested for loop works:

adj = ["red", "big", "tasty"]
fruits = ["apple", "banana", "cherry"]
for a in adj:
   for f in fruits:
       print(a, f)

Output:

red apple
red banana
red cherry
big apple
big banana
big cherry
tasty apple
tasty banana
tasty cherry

Here, we have two lists, adj and fruits. We use a nested for loop to iterate over both lists simultaneously, and print each combination of an adjective and a fruit on a new line. （在这里，我们有两个列表， adj和fruits。我们使用嵌套的for循环同时迭代两个列表，并在新行上打印形容词和水果的每个组合。）

Conclusion #

Conclusion （结论）

In conclusion, we have learned about the for loop in Python, which is an important construct used to iterate over a sequence. We have seen how the range function can be used to generate a sequence of numbers, and how nested for loops can be used to iterate over multiple sequences simultaneously. With this knowledge, you （总之，我们已经了解了Python中的for循环，它是用于迭代序列的重要构造。我们已经看到如何使用range函数生成一系列数字，以及如何使用nested for循环同时迭代多个序列。有了这些知识，您）