09-python_流程控制-for-while

循环 
 - for
 - while

1. 概念

   当条件满足时, 使某段代码重复执行多次

2. 语法

 2.1 遍历序列
    for iterating_var in sequence :
        statement(s)

 2.2 指定循环次数 
    - range([start,] end [,step]) 快速生成List
    for iterating_var in range(0, max_time) :
        statement(s)

 2.3 注意   
    iterating_var 是局部变量, 只在for循环内有效

3. 举例

---------------2.1---------------------
for char in "abc" :
    print char, "- I'm Mr String"

for num in [1,2,3] :
    print num, "--- I'm Mr List"

for key in {1:"x", 2:"y"} :
    print key, "------ I'm Mr Dict" 
---------------------------------------
---------------2.2---------------------
sum = 0

for num in range(1, 101) :
    sum += num

print "1+2+3+...+99+100 = ", sum
---------------------------------------
count = 1
sum = 0

for x in range(100) :
    sum += count
    count += 1

print "sum = ", sum
---------------------------------------

4. 遍历 sequence

 4.1 value
    for iterating_var in sequence :
        print iterating_var

 4.2 index
    seq = "abc"
    for index in range( len(seq) ) :
        print seq[index]

5. 遍历 dict

 5.1 for
   5.1.1 取key   - dictName | dictName.keys()
   ----------------------------------------------
    myDict = {1:'a', 2:'b', 3:'c'}
    for key in myDict :
        print key, "=", myDict[key]

    for key in myDict.keys() :
        print key, "=", myDict[key] 
   ----------------------------------------------

   5.1.2 取value - dictName.values()
   ----------------------------------------------
    myDict = {1:'a', 2:'b', 3:'c'}
    for value in myDict.values() :
        print value
   ----------------------------------------------

   5.1.3 取键值对- dictName.items() 
   ----------------------------------------------
    myDict = {1:'a', 2:'b', 3:'c'}
    for key,value in myDict.items() :
        print key, "=", value
   ----------------------------------------------

6. 循环控制 

   - else       for循环正常结束后执行
   - beak       结束整个for循环
   - continue   结束当次for循环
   - pass       代码桩
   - exit()     结束整个程序

 6.1 for 的 else子句
  6.1.1 语法
    for ...
        ...
    else:
        ...

  6.1.2 说明
    for循环正常执行完毕后, else子句才会执行

  6.1.3 举例
    ----------------------------------------------
    for x in [1,2] :
        print x
    else:
        print "for sentence is running over!!"

    ---output---
    1
    2
    for sentence is running over!!
    ----------------------------------------------

 6.2 break - 终止循环
    ----------------------------------------------
    for x in [1,2] :
        print x
        if 2 == x :
            print "break for sentence"
            break;
    else:
        print "for sentence is running over!!"

    ---output---
    1
    2
    break for sentence
    ----------------------------------------------

 6.3 continue - 终止当次循环
    ----------------------------------------------
    for x in [1,2,3] :
        if 2 == x :
            continue
        print x
    else :
        print "for sentence running over!!"

    ---output---
    1
    3
    for sentence running over!!
    ----------------------------------------------

 6.4 pass - 代码桩, 占位的作用
    >>> if 1 :
    ...
      File "<stdin>", line 2
        ^
    IndentationError: expected an indented block
    >>> if 1 :
    ...     pass
    ...
    >>>

 6.5 exit()
    ----------------------------------------------
    for x in range(5) :
        print x
        if 3 == x :
            exit()
    else :
        print "for is over!!"

    print "#" * 10    

    ---output---
    0
    1
    2
    3    
    ----------------------------------------------

7. while

 7.1 语法
    while expression :
        statement(s)
    [else:
        statement(s)
    ]
 7.2 举例
    ----------------------------------------------
    count = 0
    times = 10
    while True :
        print count , "hello!!"
        ###
        count += 1
        if times == count :
            break;
    ----------------------------------------------