python笔记（8)----条件、循环及其他语句

print和import的更多信息


print可以打印多个表达式，用逗号分开就行，


从模块导入函数
import somemodule
from somemodule import somefunction
from somemodule import somefunction ,anotherfunction,yetanotherfunction
from somemodule import*


序列解包
x,y,z,= 1,2,3
print x,y,z
结果：
1 2 3


链式赋值
将同一个值赋给多个变量的捷径
x=y=somefunction


增量赋值
x+=1
x*=1


布尔
print bool (42),bool(''),bool(0),bool('I think')
True False False True
注意：false none 0 "" () [] {}会被解释器看作假（false）


if elif else 语句


num = input('enter a number: ')
if num > 0:
    print 'the number is positive'
elif num < 0:
    print 'the number is negative'
else:
    print 'the number is zero'


enter a number: -1
the number is negative


嵌套
name = raw_input('what is your name?: ')
if name.endswith('luo'):
    if name.startswith('mr.'):
        print 'hello ,mr.luo'
    elif name.startswith ('mrs.'):
         print 'hello ,mrs.luo'
    else:
        print 'hello,luo'
else:
    print 'hello, stranger'
结果：
what is your name?: mrs.luo
hello ,mrs.luo


使用==运算符判定两个对象是否相等，使用is判定两个对象是否等同（同一个对象）


in：成员资格运算符


布尔运算符
and、or、not就是所谓的布尔运算符
示例：
numbers = input ('enter a number between 1 and 10:')
if numbers <=10 and numbers>=0:
    print "is great"
else:
    print "wrong"
结果:
enter a number between 1 and 10:2
is great


while 循环
x = 1
while x<=100:
    print x
    x+=1


部分结果;
94
95
96
97
98
99
100


name = ''
while not name:
    name = raw_input("enter your name: ")
    print 'hello,%s!'% name
结果：
enter your name: luo
hello,luo!


for循环
示例：
numbers=[0,1,2,3,4]
for number in numbers:
    print number
结果：
0
1
2
3
4




for number in range(1,101):
    print number


部分结果：
94
95
96
97
98
99
100


循环遍历字典元素，
d = {'x':1,'y':2,'z':3}
for key in d:
    print key,'corresponds to',d[key]


结果:
y corresponds to 2
x corresponds to 1
z corresponds to 3


并行迭代
示例：
name = ['x','y','z']
age = [12,13,14]
for i in range(len(name)):
    print name[i],'is',age[i],'years old'
结果：
x is 12 years old
y is 13 years old
z is 14 years old
编号迭代
示例：
ndex = 0


strings = ["asd", "123", "aXXX", "cc123XXX123"]


for str in strings:
    if 'XXX' in str:
        strings[index] = 'luo'
    index += 1


print strings
结果：
['asd', '123', 'luo', 'luo']
反转和排序迭代
示例：
print list( reversed('hello world'))
print ''.join(reversed('hello world'))
结果：
['d', 'l', 'r', 'o', 'w', ' ', 'o', 'l', 'l', 'e', 'h']
dlrow olleh


跳出循环
1、break
2、continue
3、while True/break习语
示例：
while True:
    word = raw_input('please enter a word: ')
    if not word:break
    print 'the word was '+ word


结果：
please enter a word: 1
the word was 1
please enter a word: hello
the word was hello
please enter a word: 


1、pass
2、del
3、exec和eval
示例：
exec "print 'hello,world' "
结果：
hello,world


示例：
while True:
   print eval(raw_input ('enter an arithmetic expression: '))
结果：
enter an arithmetic expression: 4*2+9
17
enter an arithmetic expression: 6/3+10
12
enter an arithmetic expression: