python之循环

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一、for循环

注：python shell ，使用ctrl+n创建一个文件，编辑完成保存，按F5执行。

1、命名循环变量
for year in range(1980,2020):
print 'in the {} ...'.format(year)
============= RESTART: C:/Users/vinsuan/Desktop/python笔记/1.py =============
in the 1980 ...
in the 1981 ...
in the 1982 ...
in the 1983 ...
in the 1984 ...
in the 1985 ...
in the 1986 ...
in the 1987 ...
in the 1988 ...
in the 1989 ...
in the 1990 ...
in the 1991 ...
in the 1992 ...
in the 1993 ...
in the 1994 ...
in the 1995 ...
in the 1996 ...
in the 1997 ...
in the 1998 ...
in the 1999 ...
in the 2000 ...
in the 2001 ...
in the 2002 ...
in the 2003 ...
in the 2004 ...
in the 2005 ...
in the 2006 ...
in the 2007 ...
in the 2008 ...
in the 2009 ...
in the 2010 ...
in the 2011 ...
in the 2012 ...
in the 2013 ...
in the 2014 ...
in the 2015 ...
in the 2016 ...
in the 2017 ...
in the 2018 ...
in the 2019 ...

二、遍历列表
cats = ['manx','tabby','calico']
for cat in cats:
print "that's a nice {} you...".format(cat)
============= RESTART: C:/Users/vinsuan/Desktop/python笔记/1.py =============
that's a nice manx you...
that's a nice tabby you...
that's a nice calico you...

三、跳到下一个列表项
numbers = [5,2,0,20,30]
for num in numbers:
if num == 0:
print "you give me a 0"
continue
new_num = 100.0/num
print "100/{} = {} ".format(num,new_num)
============= RESTART: C:/Users/vinsuan/Desktop/python笔记/2.py =============
100/5 = 20.0
100/2 = 50.0
you give me a 0
100/20 = 5.0
100/30 = 3.33333333333

四、跳出循环
4.1 不带else
cart = [50.25,20.0,120,88,99]
for item in cart:
print item
if item > 100:
print "item >100"
break
============= RESTART: C:/Users/vinsuan/Desktop/python笔记/3.py =============
50.25
20.0
120
item >100

4.2带else
4.2.1情况一
cart = [50.25,20.0,120,88,99]
for item in cart:
print item
if item > 100:
print "item >100"
break
else:
print "hello"
============= RESTART: C:/Users/vinsuan/Desktop/python笔记/3.py =============
50.25
20.0
120
item >100
4.2.2情况二
cart = [50.25,20.0,12,88,99]
for item in cart:
print item
if item > 100:
print "item >100"
break
else:
print "hello"
============= RESTART: C:/Users/vinsuan/Desktop/python笔记/3.py =============
50.25
20.0
12
88
99
hello

>>> item
99
注：1、可以在while和for循环中使用else语句，在循环中使用时，else子句只在循环完成后执行，也就是说break语句也会跳过else块。
2、for循环创建的变量在for循环完成后并不会消失。因此，这个变量会包含列表中的最后一个值

五、while循环
age = raw_input("please input age (eg.30):")
while not age.isdigit():
print "I'am sorry , but {} isn't valid.".format(age)
age = raw_input("please input age (eg.30):")
print "thanks! Your age is set to {}".format(age)

============= RESTART: C:/Users/vinsuan/Desktop/python笔记/4.py =============
please input age (eg.30):34 years
I'am sorry , but 34 years isn't valid.
please input age (eg.30):44
thanks! Your age is set to 44

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