09-python_流程控制-for-while

分手后的思念是犯贱 2022-09-17 06:29 192阅读 0赞

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;  
\----------------------------------------------