Second, the Python Foundation---cycle--condition judgment (While-for-if-elif-else)

！！！ Statement!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

1. code example: #if语句

#!/usr/bin/python3

#_ *_coding:utf-8_*_

num = 10

if num = = 10:

Print (' pair ')

Operation Result:

[email protected] ~]# python if.py

Right

2. Complex if statement #注意事项: Be sure to pay attention to the Chinese and English format, statement indentation, indentation for 4 spaces, remember!!!

Code instance: if statement

#!/usr/bin/python3

#_ *_coding:utf-8_*_

XGJ = ' HTUIDC '

if xgj = = ' HTUIDC ':

xuesheng={' QQQ ': ' 1001 ', ' wwww ': ' 1002 ', ' eee ': ' 1003 '}

Print (' Number of dictionary elements:%d '%len (Xuesheng) ')

Xuesheng.clear ()

Print (' Number of elements after dictionary deletion:%d '%len (Xuesheng))

Operation Result:

Number of dictionary elements: 3

Number of elements after dictionary deletion: 0

3.else Statement #我理解的else的意思是 Otherwise, if how what happens otherwise else what happens, else is not a standalone statement, only as part of the IF statement.

code example:

#!/usr/bin/python3

#_ *_coding:utf-8_*_

num = 10

If num > 10:

Print (' wrong ')

Else

Print (' other ')

Operation Result:

Other

A 4.elif statement #elif是else与if的简写, meaning the conditional else statement, which needs to be judged again.

code example:

#!/usr/bin/python3

#_ *_coding:utf-8_*_

num = 10

If num > 10:

Print (' wrong ')

elif 0 <= Num >=10:

Print (' In an interval ')

Else

Print (' other ')

Operation Result:

In an interval

Nested code blocks

code example:

#!/usr/bin/env Python3

#!/-*-coding-utf-8-*-

num = 10

If num%2==0:

If num%3==0:

Print (' The number you enter can be divisible by 2 and 3 ')

Elif num%4==0:

Print (' The number you enter can be divisible by 2 and 4 ')

Else

Print (' The number you enter can be divisible by 2, but not divisible by 3 and 4 ')

Else

If num%3==0:

Print (' The number you enter can be divisible by 3, but not divisible by 2 ')

Else

Print (' The number you entered cannot be divisible by 2 and 3 ')

Operation Result:

The number you enter can be divisible by 2, but not divisible by 3 and 4.

！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！

is identity operator

>>> x=y=[1,2]

>>> z=[1,2]

>>> x==y

True

>>> x==z

True

>>> y==z

True

>>> x is y

True

>>> X is Z

False

# # #虽然值相同, but not in an object

>>> x is not Z

True

！！！！！！ Cycle!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

1.while Cycle

code example:

#!/usr/bin/python3

#!_*_coding:utf-8_*_

N=1

While n<=1000:

Print (' Current number is: ', n ')

N +=1

Operation Result:

The current number is: 1

The current number is: 2

The current number is: ...

The current number is: 999

The current number is: 1000

2.for Cycle

code example:

#!/usr/bin/python3

#!-*-coding:utf-8-*-

N=0 #进行赋值

Fields=[' A ', ' B ', ' C '] #进行赋值

While N<len (fields): #条件判断---If n is less than the length of the fields

Print (Fields[n]) #打印fields的0索引位置

N+=1 #加法赋值运算符 n=n+1

Operation Result:

A

B

C

code example:

htuidc=[' 1 ', ' 2 ', ' 3 '] #赋值

For DL in HTUIDC: #for in loop printing

Print (DL) #进行打印

Operation Result:

1

2

3

# # #注意事项: If you can use a for loop, try not to use the WHILE loop!!!

！！！ Iterative TOOLS!!!!!

1. Parallel iterations

code example:

#!/usr/bin/python3

#!-*-coding:utf-8-*-

student1=[' qqq ', ' www ', ' eee ']

NUMBER=[1001,1002,1003]

For I in range (len (student1)):

Print (Number[i])

htu=[' d ', ' l ']

IDC=[1001,1002,1003]

For XGJ,DH in Zip (HTU,IDC):

Print (XGJ)

xgj=[' 1 ', ' 2 ']

DH=[1001,1002]

For HTU,IDC in Zip (XGJ,DH):

Print (IDC)

Operation Result:

1001

1002

1003

D

L

1001

1002

# # #注意: The ZIP function can act on any number of sequences.

！！！！！！！ Jump out of the loop!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

1.break statements are used in the while and for loops

code example:

#!/usr/bin/python3

#!/-*-coding:utf-8-*-

For letter in ' Hello ':

If letter = = ' L ': #遍历打印, know loop print to L bounce loop

Break

Print (' Current letters: ', letter)

num = 10

While num > 0:

Print (' Output number: ', num)

num-= 1

if num = = 8: #遍历打印输出, know equals 8 jumps out of the loop

Break

Operation Result:

The current letter is: H

The current letter is: E

Output numbers are: 10

Output numbers are: 9

2.continue #跳出当前的循环, then the next round of the loop----can only jump out once

code example:

#!/usr/bin/python3

#!/-*-coding:utf-8-*-

For letter in ' Hello ':

If letter = = ' L ': #遍历打印, know loop print to L bounce loop, then out L resume print loop

Continue

Print (' Current letters: ', letter)

Operation Result:

H

E

O

Else clause in a loop

1. Using else in while

code example:

num = 0

While num < 3:

Print (num, ' less than 3 ')

num = num + 1

Else

Print (num, ' greater than or equal to 3 ')

Print (' End Loop ')

Operation Result:

0 less than 3

1 less than 3

2 Less than 3

3 is greater than or equal to 3

End Loop

2. Using else in for

code example:

#!/usr/bin/python3

#!/-*-coding:utf-8-*-

names = [' Xiaomeng ', ' Xiaozhi ']

For name in Names:

If name = = ' Xiao ':

Print (' name: ', name)

Break

Print (' Circular Name list ' +name)

Else

Print (' No looping data ')

Print (' End Loop ')

Operation Result:

Circular Name List Xiaomeng

Circular Name List Xiaozhi

No cyclic data

End Loop

！！！ PASS STATEMENT!!!!!!

Pass is an empty statement #就是什么都不做的语句, only a placeholder statement.

#!/usr/bin/python3

#!/-*-coding:utf-8-*-

XGJ = ' HTUIDC '

if xgj = = ' HTUIDC ':

Print (' pair ')

elif Xgj = = ' Idchtu ':

Pass # # #如果没有这个占位语句就会出错

Else

Print (' wrong ')

Operation Result:

Right

To be Continued ... This chapter is chapter II

Follow-up continue chapter III

Two, the Python foundation---loop--condition judgment (while-for-if-elif-else)