Python语言之控制流(if...elif...else,while,for,break,continue)

1.if...elif...else...

 number = 23
 guess = int(input('Enter an integer : '))
 
 if guess == number:
     print( 'Congratulations, you guessed it.' ) # New block starts here
     print( "(but you do not win any prizes!)" ) # New block ends here
 elif guess < number:
     print( 'No, it is a little higher than that' )# Another block
 else:
     print( 'No, it is a little lower than that' )
 
 print( 'Done' )
 # This last statement is always executed, after the if statement is executed

2.while

 number = 23
 running = True
 
 while running:
     guess = int(input('Enter an integer : '))
 
     if guess == number:
         print( 'Congratulations, you guessed it.' )
         running = False # this causes the while loop to stop
     elif guess < number:
         print( 'No, it is a little higher than that' )
     else:
         print( 'No, it is a little lower than that' )
 else:
     print( 'The while loop is over.' )
     # Do anything else you want to do here
 
 print( 'Done' )

while循环条件变为False时，else块被执行。

你可能想问，这样的else块始终会被执行到，还要else干嘛。别着急，在4.break中有解答。

3.for

 for i in range(1, 5):
     print( i )
 else:
     print ( 'The for loop is over' )

range(n, m [,stepLen]) = [n,n+stepLen,n+stepLen*2,...,n+(ceil((m-n)/stepLen)-1)*stepLen]

即从n开始，以stepLen为步长，一直到小于m的序列（不包括m）。默认情况下stepLen=1。

4.break

终止当前循环语句。

注意如果从for或while循环终止，任何对应的else将不会被执行。

5.continue

跳过当前循环块中的剩余语句，然后继续进行下一轮的循环。