Scripting Language Learning (six)

Cyclic structure of the program

Traversal cycle

Format :

for 循环变量 in 遍历结构 :
    语句块

• It can be extracted one by one from the traversing element into the loop variable in the structure
• Traversing the structure contains many types
• Each cycle element is obtained from a structure placed traversing the loop variable, and perform a block.

Application :

• Count cycle (N times): a traversing range(N)or range(M,N,K)number sequence generation, resulting in circulation.

for i in range(N):
    语句块

• String traversal cycle

for c in s :
    语句块

• Where s is a string, c representative of each character in the string.
• Removed from the string sequentially into each character c in circulation.

Examples :

• List traversal cycle

for item in ls :
    语句块

 + -ls是一个列表，遍历列表的每一个元素，产生循环

• File traversal cycle

for line in fi :
    语句块

  + -fi是一个文件标识符，遍历这个文件的每行，产生循环
  + 文件标识符相当于用一个变量来标识系统中的一个文件

Infinite loop

• Infinite loop circulation operation is controlled by the conditions

while 条件 :
    语句块

• When the program runs can not be stopped, you can ctrl + c to exit the run

Like reserved words break the cycle and continue to control the usage and C language

Cycle and else

for 循环变量 in 遍历结构 :
    语句块1
else :
    语句块2
或者
while 条件 :
    语句块1
else :
    语句块2

• When the cycle is not exit the break statement, the else block of statements
• else block cycle can be completed as a normal reward

example: