For loop and while loop in Python

for loop

It is often used to traverse strings 、 list 、 Tuples 、 Dictionaries 、 Set and other sequence types , Get the elements of the sequence one by one ,python Medium for The loop needs to specify the scope of the iteration .

His format is usually ：
for    Variable      in      character string | list | Tuples | Dictionaries | aggregate ：

for example ： seek 1~100 and

sum=0

for i in range（1,101）

   sum +=i

print（sum）

User login program

1. Enter your username and password

2. Determine whether the user name and password are correct ('name==root','passwd='123')

3. In order to prevent violent cracking , There are only three logins , If you have more than three chances , Report errors

About ending a cycle , There are several ways

break Out of the loop The contents after the loop will not be executed  break Statement used in while and for In circulation , If you use nested loops ,break Statement will stop executing the deepest loop , And start executing the next line of code

continue Jump out of this cycle ,continue The following code content will not be executed

exit() End the whole program

pass Do nothing , It only plays a space occupying role

while loop

while The grammatical structure of a loop is ：

while Judgment statement , Execute statement

He and for The difference between cycles is :for The loop needs to add an iterative object or range , and while Circulation does not ;

This is the user name and password above , Switch to while The loop method completes ;

i=0

while i <3:

name = input (" user name ：")

passward=input（“ password ：”）

if name==“root”and passward==“123”：

print（“ Login successful ”）

break

else：

print（“ Login failed ”）

print（“ You still have %d Second chance ”%（2-i）)）

i+=1

else:

print(" Log in more than 3 Please wait 100s Try again later ！！！")