Preface
The for loop is a type of loop used many in python development and requires proficiency.
Use scenarios of for loop
- The for loop is used to repeat a specific number of operations
- The for loop is mainly used to traverse, loop, lists, collections, dictionaries, files, and even custom classes or functions.
Example demonstration of for loop operation list
- Use for loops are often combined with if statements to traverse elements, modify elements, delete elements, and count the number of elements in the list.
The for loop is used to traverse the entire list
#for循环主要用来遍历、循环、序列、集合、字典
Fruits = ['apple','orange','banana','grape']
for fruit in Fruits:
print(fruit)
print("结束遍历")
结果演示：
apple
orange
banana
grape
结速遍历
The for loop is used to modify the elements in the list
#for循环主要用来遍历、循环、序列、集合、字典
#把banana改为Apple
Fruits=['apple','orange','banana','grape']
for i in range(len(Fruits)):
if Fruits[i] == 'banana':
Fruits[i] ='apple'
print(Fruits)
结果演示：['apple', 'orange', 'apple', 'grape']
3. The for loop is used to delete elements in the list
Fruits=['apple','orange','banana','grape']
for i in Fruits:
if i == 'banana':
Fruits.remove(i)
print(Fruits)
结果演示：['apple', 'orange', 'grape']
The for loop counts the number of an element in the list
#统计apple的个数
Fruits = ['apple','orange','banana','grape','apple']
count = 0
for i in Fruits:
if i=='apple':
count+=1
print("Fruits列表中apple的个数="+str(count)+"个")
结果演示：Fruits列表中apple的个数=2个
Note: You can also use Fruit.count(object) for certain data statistics in the list
The for loop realizes the multiplication of 1 to 9
sum=1
for i in list(range(1,10)):
sum *= i
print("1*2...*9=" + str(sum))
结果演示：1*2...*10=362880
Iterate over the string
for str in 'abc':
print(str)
结果演示：
a
b
c
Iterate over collection objects
for str in {
'a',2,'bc'}:
print(str)
结果演示：
a
2
bc
Iterate over files
for content in open("D:\\test.txt"):
print(content)
结果演示：
朝辞白帝彩云间，千里江陵一日还。
两岸猿声啼不住，轻舟已过万重山。
Iterate over the dictionary
for key,value in {
"name":'伤心的辣条',"age":22}.items():
print("键---"+key)
print("值---"+str(value))
结果演示：
键---name
值---伤心的辣条
键---age
值---22
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