A brief summary of judgment statements and loop statements in Python (with examples)

This article brings you a simple summary of judgment statements and loop statements in Python (with examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Today I will mainly introduce if judgment and loop control in Python.
Originally the title I wrote before was "Python's flow control", but after thinking about it, I realized that flow control is not limited to conditional judgment and loop control. So I changed it honestly...aha

1. If conditional judgment

1. Grammar form

if conditions The judgment syntax form is as follows. The corresponding execution operation is determined based on the conditional judgment of each branch.

if <条件判断-1>:
    <操作-1>
elif <条件判断-2>:
    <操作-2>
elif <条件判断-3>:
    <操作-3>
else：
    <操作-4>

• if branch: If is judged to be true, then go to the execution of , otherwise go to the elif statement at;

• elif: is the abbreviation of "else if". elif statements can exist, or there can be one or more. When entering this branch, if the judgment is true, then execute , otherwise, go to the next elif statement or else statement.

• ##else: When all the above if and elif branches are completed, if they are all judged to be false, then finally enter the else branch and perform .

For example: value = x if x

2. A special formif judgment also has a special form. As follows.
It determines whether to execute based on the value of x. Among them, when x is a non-zero value, a non-empty string, a non-empty list, etc., it is judged to be True, and the execution is transferred to , otherwise it is not executed.

if x :
    <actions>

2. The for loop

When I introduced the data types before, I introduced this part, so let’s briefly summarize it!

is as follows:

for x in 可迭代序列：
    <actions>

• This loop statement uses x as a temporary variable to iterate out each element in the iterable object (string, list, tuple, etc.) in turn.

As a simple example, when there are different types of elements in the list data type x, how to read and print out each element?

the_count = [1,2,3,4,5]                           # %d
fruits = ['apples','oranges','pears','apricots']  # %s
change = [1,'pennies',2,'dimes',3,'quarters']     # mixed list：%r

for number in the_count: 
    print("this is count %d " % number)
for fruit in fruits: 
    print("a fruit of type : %s " % fruit)

# mixed lists : notice we have to use %r since we don't know what's in it
for i in change:  # %r
    print("i got %r " % i)

【Supplement】Knowledge point~ ~ ~ In fact, I suddenly remembered it^_^

• ##enumerate()

  Will The index and value of the sequence are retrieved. Let’s go straight to the example~
  

  >>> l = ['a','b','c']
  >>> for ind ,val in enumerate(l):
          print("%d %s" %(ind,val))
  ...
  0 a
  1 b
  2 c

• sorted( )

  Form: sorted([sequence], key=function, reverse =True or False) Parsing: Receive a sequence and sort it. You can also sort based on the specified key form. The parameter reverse is the direction sorting, which takes effect when True.
  For example:
  
  

  # 对list进行排序。
  >>> sorted([36,5,-12,9,-21])
  [-21, -12, 5, 9, 36]
  
  # 高阶函数
  # 可以接收一个key函数来实现自定义的排序，例如，按照绝对值大小排序：
  >>> sorted([36,5,-12,9,-21],key=abs)
  [5, 9, -12, -21, 36]
  
  # 对字符串进行排序，默认情况下是按照首字母的ASCII的大小进行排序。
  >>> sorted( ['bob','about','Zoo','Credit'] )
  ['Credit', 'Zoo', 'about', 'bob']
  
  # 忽略大小写的排序：（全部换成小写）
  >>> sorted( ['bob','about','Zoo','Credit'] ,key=str.lower)
  ['about', 'bob', 'Credit', 'Zoo']
  
  # 忽略大小写，且进行方向排序：
  >>> sorted( ['bob','about','Zoo','Credit'] ,key=str.lower,reverse= True)
  ['Zoo', 'Credit', 'bob', 'about']

3. while loop

Grammar form:

• while <expression>:
      <actions>

Analysis: As long as the condition is satisfied, the loop body will be continuously executed until the condition is not satisfied, then the loop will exit.
For example:

i = 0
numbers = []
while i < 6 :
    print("at the top i is %d " % i)
    numbers.append(i)  
    i = i + 1
    print("numbers now : ",numbers)
    print("at the bottom i is %d " %i)
    # 当i=6时 退出循环
print("the numbers: ")

4. break

break keyword, its function is to exit the current layer loop early.

For example:

while x<10 :
    if <判断-1>： #例如 x==3
        break
    x + = 1

When is true, execute the break statement and exit the loop.

5. continue

The continue keyword is used to skip the loop immediately through the continue statement during the loop. , return to the top of the loop and start the next loop directly.

For example:

while x<10 :
      if <判断-1>： #例如 x==3
          break
      print(x)
      x + = 1

Related recommendations:

Conditional judgment and looping in Python

Conditional judgment in Python Summary of usage of statements and loop statements

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