Python's flow control can be divided into three categories: sequential structure, branch structure , loop structure
One, the sequence structure
As the name implies, the sequence structure determines the execution order of the code, and the execution flow of Python code is from top to bottom. If the intermediary is blocked during execution, it will not continue to execute, and will continue to execute until the end of the blocking .
Second, the branch structure
When the code with a simple branch structure is executed to a certain position, a selection judgment is made to absolutely continue the direction of execution. A frequently used branch structure is the if statement. An if statement is a simple logical execution sequence that selects the execution location of the code through a judgment condition.
2.1 bool type
boolean type
There are only two possibilities for this type of value, that is, his value is only true and false.
There are several ways to represent truth in python
True: Indicates that the judgment result is true, that is, the condition is established
1: Indicates that the judgment result is true, that is, the condition is established
There are several ways to represent false in python
False: indicates that the judgment result is false, that is, the condition is not established
0: indicates that the judgment result is false, that is, the condition is not established
"": This is an empty string, which also means that the judgment result is false, that is, the condition is not established
2.2 if syntax format
Single branch: only judge one condition, and only specify the code to be executed when the condition is true
Syntax format:
if a < b : #判断a是否小于b条件满足执行下边代码
print("a小于b") #输出a小于b
Double branch: only judges one condition, but not only specifies the code to be executed when the condition is established, but also specifies the code to be executed when the condition is not established
Syntax format:
if a < b : #判断a是否小于b条件满足执行下边代码
print("a小于b") #输出a小于b
else : #上面代码执行正常执行完毕执行else中的内容
print("a大于b")
Multi-branch: You can judge multiple conditions, meet different conditions, and execute different codes
Syntax format:
if a < b :
print("a小于b")
elif a > b :
print("a大于b")
elif a == b :
print("a等于b")
elif a + b > i :
print("a加b大于i")Third, the loop structure
When the code is executed in sequence, the condition is judged when it reaches a certain position. When the condition is met, the loop body of the statement is executed, and when the condition is not met, the loop body is skipped and the code continues to be executed. There are two built-in loop structures, while and for. For can be used to perform loop logic. It is often used to traverse a container and process the elements in the container through the loop body in turn.
3.1 while loop
while loop is suitable for not sure how many times to use the loop
Format 1:
while a > b: #判断是否满足条件，满足条件执行下边代码
代码代码代码Working logic [execution process]
Step 1: First determine whether the conditions are met
If it is satisfied: start executing the code in the loop, after the code is executed, judge whether the condition is satisfied again
If not satisfied: skip the loop
Format 2:
while 判断条件:
代码1代码1代码1
else: # else中的代码当while循环中的代码执行完成以后，才会执行
代码2代码2When the condition is met, code 1 will be executed.
When the condition is not met, code 2 will be executed.
3.2 for loop
The difference between the use of for and while loops
The while loop is suitable for use in infinite loops or when the number of loops is uncertain. The
for loop is suitable for use when the number of loops is clear.
Format:
for 变量 in
列表:代码1代码1
else: # 当for循环结束的时候，才会去执行else中的代码2代码2代码2range method
range() returns an iterable object (the type is an object), not a list type, so the list will not be printed when printing
range(start, stop, step)3.3 Loop Control
break: When in the loop, execute to break, the loop stops immediately
continue: When in the loop, execute to continue, terminate the current loop, and directly start the next loop