Python的流程控制
Python的流程控制：
-
判断
可以通过下图来简单了解条件语句的执行过程:
语法：
# 用法1 if 判断条件: 执行语句 else: 执行语句 # 用法2 if 判断条件1: 执行语句1 elif 判断条件2: 执行语句2 elif 判断条件3: 执行语句3 else: 执行语句4
实例：
# 方法一实例:
>>> candition = bool(True)
>>> if candition :
... print("Yes")
... else:
... print("No")
...
Yes
>>> candition = bool(False)
>>> if candition :
... print("Yes")
... else:
... print("No")
...
No
# 方法二实例:
>>> def judge(number):
... if number == 0 :
... print("zero")
... elif number == 1 :
... print("one")
... elif number == 2 :
... print("two")
... else :
... print("Error")
...
>>> judge(0)
zero
>>> judge(1)
one
>>> judge(5)
Error
-
循环
while循环
Python 编程中 while 语句用于循环执行程序，即在某条件下，循环执行某段程序，以处理需要重复处理的相同任务。
语法：
# 用法
while 判断条件: 执行语句
else:
执行语句
实例：
>>> n = 0
>>> while n <= 10 :
... print("number is %d: " %n)
... n += 1
... else :
... print("while end in: %s" %n)
...
number is 0:
number is 1:
number is 2:
number is 3:
number is 4:
number is 5:
number is 6:
number is 7:
number is 8:
number is 9:
number is 10:
while end in: 11
for
Python for循环可以遍历任何序列的项目，如一个列表或者一个字符串。
语法：
for 项目 in 集合: 执行语句 “项目”为遍历集合内的元素
实例：
# 实例1:
>>> sequence_list = ["itme-1","item-2","item-3","itme-4"]
>>> for item in sequence_list :
... print("Itme is: %s" %item)
...
Itme is: itme-1
Itme is: item-2
Itme is: item-3
Itme is: itme-4
# 实例2:
>>> sequence_str = "ABCD"
>>> for item in sequence_str :
... print("Str is: %s" %item)
...
Str is: A
Str is: B
Str is: C
Str is: D
>>>
# 实例3:
>>> for num in range(5):
... print("Number is: %d" %num )
...
Number is: 0
Number is: 1
Number is: 2
Number is: 3
Number is: 4
-
跳出循环
- break
- continue
* break跳出整个循环，而continue 语句是跳出本次循环。
break
break语句用来终止循环语句。break语句用在while和for循环中将停止执行最深层的循环，并开始执行下一行代码。
实例：
# 实例：
>>> sequence_str = "ABCD"
>>> for item in sequence_str :
... print("Itme is: %s" %item)
... if item == "C" :
... break
...
Itme is: A
Itme is: B
Itme is: C
continue：
continue语句用在while和for循环中，用来告诉Python跳过当前循环的剩余语句，然后继续进行下一轮循环。
实例:
# 实例:
>>> sequence_str = "ABCD"
>>> for item in sequence_str :
... if item == "B":
... continue
... print("Itme is: %s" %item)
...
Itme is: A
Itme is: C
Itme is: D
