第五章：条件、循环和其它语句

print ‘Age‘,42
print 1,2,3

>>> name = ‘Gumby‘
>>> salutation = ‘Mr.‘
>>> greeting = ‘Hello‘
>>> print greeting,salutation,name
Hello Mr. Gumby
>>> print greeting + ‘,‘,salutation,name
Hello, Mr. Gumby
>>> print greeting,‘,‘,salutation,name
Hello , Mr. Gumby

import somemodule
from somemodule import somefunction
from somemodule import somefunction1 somefunction2 somefunction3
from somemodule import *

>>> import math as foobar
>>> print foobar.sqrt(9)
3.0

>>> from math import sqrt as foobar
>>> foobar(4)
2.0

>>> x,y,z = 1,2,3
>>> print x,y,z
1 2 3

>>> y=x
>>> print x,y,z
1 1 3
>>> x,z=z,x
>>> print x,y,z
3 1 1

>>> dd = {‘name‘:‘Anti‘,‘Age‘:42}
>>> key,value = dd.popitem()
>>> key
‘Age‘
>>> value
42

x = y = somefunction()
#
y = somefunction()
x = y

x = somefunction()
y = somefunction()

>>> x = 2
>>> x += 1  #加等
>>> x
3
>>> x *= 6  #乘等
>>> x
18
>>> x -= 2  #减等
>>> x
16

>>> bool(‘I think, therefor I am.‘)
True
>>> bool([])
False
>>> bool({‘name‘:‘Aoto‘})
True
>>> bool(0)
False

name = raw_input("What‘s your name ? ")
if name.endswith(‘Gumby‘):
    print ‘Hello, Mr.Gumby.‘
else:
    print ‘Hello, stranger.‘
#输出如下
What‘s your name ? Gumby
Hello, Mr.Gumby.

if ...:
    do ...
elif ...:
    do ...
else:
    do ...

>>> x = y = [1,2,3]
>>> z = [1,2,3]
>>> x == y
True
>>> x == z
True
>>> x is y
True
>>> x is z
False      #注意

number = input(‘Enter a number between 1 and 10 : ‘)
if number <= 10 and number > 1:
    print ‘Great!‘
else:
    print ‘Wrong!‘

#输出如下
Enter a number between 1 and 10 : 8
Great!

name = raw_input(‘Please input your name: ‘) or ‘<Unknow>‘
print name


#输出如下：
Please input your name: 
<Unknow>


#输出如下：
Please input your name: Aoto
Aoto

a if b else c

x=2 if 10>=2 else 4
print x


result = ‘gt‘ if 1 >3 else ‘lt‘
print result

if not condition:
    crash program

>>> age = 10
>>> assert 0 < age < 100
>>> age = -1
>>> assert 0 < age < 100
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError

>>> age = -1
>>> assert 0 < age < 100, ‘The age must be reallistic.‘
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError: The age must be reallistic.

name = ‘‘
while not name or name.isspace():
    name = raw_input(‘Please enter your name: ‘)
print ‘Hello,%s!‘ % name
#输出如下：
Please enter your name:    
Please enter your name:  #输入空格是无效的，要求重新输入
Please enter your name: dodo
Hello,dodo!

kl = []
for i in range(1,10,2):
    kl.append(i)
print kl


#输出如下
[1, 3, 5, 7, 9]

>>> d = {‘name‘:‘ToTo‘,‘Age‘:23,‘Address‘:‘BeiJing‘}
>>> for key in d:
...     print key,‘corresponds to‘,d[key]
... 
Age corresponds to 23
name corresponds to ToTo
Address corresponds to BeiJing

>>> for k,v in d.items():
...     print k,‘corresponds to‘,v
... 
Age corresponds to 23
name corresponds to ToTo
Address corresponds to BeiJing

zip(range(5),xrange(1000))
输出：[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4)]

for string in strings:
    if ‘xxx‘ in string:
        index = strings.index(string)
        strings[index] = ‘[censored]‘

index = 0
for string in strings:
    if ‘xxx‘ in string:
        strings[index] = ‘[censored]‘
    index += 1

for index,string in enumerate(strings):
    if ‘xxx‘ in string:
        string[index] = ‘[censored]‘

>>> sorted([4,3,5,2,3,6,9,0])
[0, 2, 3, 3, 4, 5, 6, 9]
>>> sorted(‘Hello,world!‘)
[‘!‘, ‘,‘, ‘H‘, ‘d‘, ‘e‘, ‘l‘, ‘l‘, ‘l‘, ‘o‘, ‘o‘, ‘r‘, ‘w‘]
>>> list(reversed(‘Hello,world!‘))
[‘!‘, ‘d‘, ‘l‘, ‘r‘, ‘o‘, ‘w‘, ‘,‘, ‘o‘, ‘l‘, ‘l‘, ‘e‘, ‘H‘]
>>> ‘‘.join(reversed(‘Hello,world!‘))
‘!dlrow,olleH‘

for x in seq:
    if condition1:continue
    if condition2:continue
    if condition3:continue
    
    do_something()
    do_something_else()
    do_another_thing()
    etc()

for x in seq:
    if not(condition1 or condition1 or condition1):
        do_something()
        do_something_else()
        do_another_thing()
        etc()

while True:
    word = raw_input(‘Please enter a word: ‘)
    if not word: break
    #处理word
    print ‘The word was ‘ + word

from math import sqrt
for n in range(99,0,-1):
    root = sqrt(n)
    if root == int(root):
        print root,n
        break
else:
    print "Don‘t find it."

>>> [x*x for x in range(5)]
[0, 1, 4, 9, 16]
>>> [x*x for x in range(10) if x%3 == 0]
[0, 9, 36, 81]
>>> [(x,y) for x in range(3) for y in range(3) if y<=x]
[(0, 0), (1, 0), (1, 1), (2, 0), (2, 1), (2, 2)]
>>> [(x,y) for x in range(3) for y in range(3)]
[(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2, 1), (2, 2)]

girls = [‘alice‘,‘bernice‘,‘clarice‘]
boys  = [‘chris‘,‘arnord‘,‘bob‘]
print [boy + ‘ + ‘ + girl for boy in boys for girl in girls if boy[0]==girl[0]]
#结果如下
[‘chris + clarice‘, ‘arnord + alice‘, ‘bob + bernice‘]

if name == ‘Raplh Auldus Melish‘:
    print "Welcome!"
elif name == ‘Enid‘:  
#在elif这个代码块中，必须要有一个执行语句，否则空代码块在Python中是非法的，解决方法就是加一个pass
    #还没完
    pass
elif name == ‘Bill Gates‘:
    print "Access Denied!"

>>> x = 1
>>> del x
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name ‘x‘ is not defined

>>> x = ["Hello",‘World‘]
>>> y = x
>>> y[1] = "python"
>>> x
[‘Hello‘, ‘python‘]

>>> del x
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name ‘x‘ is not defined
>>> y
[‘Hello‘, ‘python‘]

>>> from math import sqrt
>>> exec "sqrt = 1"
>>> sqrt(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: ‘int‘ object is not callable

>>> from math import sqrt
>>> scope = {}
>>> exec ‘sqrt = 1‘ in scope
>>> sqrt(4)
2.0
>>> scope[‘sqrt‘]
1