用于记录自己写的，或学习期间看到的不错的，小程序，持续更新……
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【例001】计算:1-2+3-4..+199-200值
代码如下:
#encoding=utf-8
#计算 1-2+3-4..+199-200值
#1+3+5+7+…199
#-2-4-6…-200
sum1 = 0
sum2 = 0
for i in range(1,200,2): #计算1+3+5+7…199
sum1 +=i
print sum1
for i in range(-200,0,2): #计算-2+(-4)+(-6)…+(-200)
sum2 +=i
print sum2
print “the total of 1-2+3-4..+199-200 is: “, sum1+sum2
【例002】将两个文件中相同的部分，写到一个文件中
代码如下:
#encoding=utf-8
#python 2.7.4
#purpose: 将文件1.txt,2.txt中相同的内容放到3.txt中;
f1 = open(“1.txt”,”r+”)
f2 = open(“2.txt”,”r+”)
f3 = open(“3.txt”,”w+”)
all1 = f1.readlines() #先拿文件1中所有行取出
all2 = f2.readlines() #再拿文件2中所有行取出
f1.close()
f2.close()
for l1 in all1:
for l2 in all2:
if l1.strip()==l2.strip(): #比较行中内容是否一样
f3.write(l2)
else:
continue
else:
pass
print “#”*40
f3.close()
【例003】反向读取文件
假如要读取的test.txt文件内容如下:
代码如下:
python
perl
java
shell
实现代码:
代码如下:
file1 = file(‘test.txt’,’r’)
list1 = [] #用一个空列表用于存放每行的内容
while true:
line = file1.readline()
list1.append(line.strip())
if len(line) == 0:
break
for l in list1[::-1]: #反向遍历，然后依次读取出来
print l
file1.close()
输出结果:
代码如下:
shell
java
perl
python
【例004】 往文件中所有添加指定的前缀
比如文中: print是一个函数
文本文件强制二进制编码
就变成了下面的
代码如下:
01.python 3.0: #print是一个函数
02.python 3.0: #文本文件强制二进制编码
#coding = gbk #中文编码
f_r = open(‘test.txt’) #打开要处理文件
f_w = open(‘file.txt’,’w’) #创建要添加文件
i = 0 #加前缀标志位
while true:
i += 1
line = f_r.readline()
if not line:
break
f_w.write(‘%02d’%(i) + ‘.python 3.0: #’ + line)#字符串格式化及拼接技巧
f_r.close() #关闭打开的文件句柄
f_w.close()
【例005】
代码如下:
#coding = gbk
””’
下面code.txt文件中内容，将
01 cn chinese
02 in india
03 hk hongkang
04 jp japan
05 de germany
06 us united states of america
要文件的内容，每一行文件，写到一个文件，且文件名前面两个字段，如
文件名为:01_cn_chinese.txt
文中内容:01 cn chinese
知识要点:
1. ”.join 和 split函数
2. 字符的联合
3. with语句,open文件
4. 遍历数组
5. 切片操作
”’
postfix = ‘.txt’ #设置后缀
with open(‘test.txt’) as myfile: #with语句打开文件为myfile
while true: #while循环拿文件读出来
lines = myfile.readlines() #拿所有的行一次性读取到列表中
if not lines: break #没有则中断
for line in lines: #遍历列表
file_out = str(‘_’.join(line.split()[:])) + postfix #得到01_cn_chinese.txt文件名
open(file_out,’w’).write(line) #write(line),将没行的文件写入新文件中
【例006】
代码如下:
#coding = gbk
””’
#最终实现下面的过程
foos = [1.0, 2.0, 3.0, 4.0, 5.0]
bars = [100, 200, 300, 400, 500]
1.0 [200, 300, 400, 500]
2.0 [100, 300, 400, 500]
3.0 [100, 200, 400, 500]
4.0 [100, 200, 300, 500]
5.0 [100, 200, 300, 400]
#知识点
1. map函数的理解
2. 关键是切片函数的应用
”’
foos = [1.0, 2.0, 3.0, 4.0, 5.0]
bars = [100, 200, 300, 400, 500]
def func(foo):
index = foos.index(foo) #foo在foos中的索引，拿她取出来
print foo,bars[:][0:index] + bars[:][index+1:]
#该索引同样在bars中相同位置，在切片的时候拿它取出，并拼接这个切片
#大功告成！
print map(func,foos)
【例007】求 6! + 5! + 4! + 3! + 2! + 1!
代码如下:
def factorial(n):
return reduce(lambda x,y: x* y, range(1,n+1))#求6!
print reduce(lambda x,y: x + y, [factorial(i) for i in range(1,6)]) #求6! + 5! + 4! + 3! + 2! + 1!
【例008】 根据输入打印文件
代码如下:
import sys
helpinfo= ””’\
this program prints files to the standard output.
any number of files can be specified.
options include:
–[version|version|v|v]: prints the version number
–[help |help |h|h]: display the help
”’
def readfile(filename):
try:
f = open(filename)
while true:
line = f.readline()
if not line:
break
print line,
except:
print ‘some error here’
if len(sys.argv) < 2: print 'no action is needed!' sys.exit() if sys.argv[1].startswith('--'): option = sys.argv[1][2:] if option in ['version','v','v','version']: print 'version 1.0' elif option in ['h','h','help','help']: print helpinfo else: print 'unknown option.' sys.exit() else: for filename in sys.argv[1:]: readfile(filename)
【例009】函数中args的用法
代码如下:
def powersum(power,*args):
””’print each argument’s power”’
total = 0
for item in args:
total += pow(item,power)
return total
print powersum(2,3,4) # (3**2) + (4**2)
print powersum(2,10) # 10**2
print powersum(2) # 0**2
【例010】匿名函数作为返回值
代码如下:
def repeater(n):
print n
return lambda s: s*n
twice = repeater(2)
print twice(‘hello’)
print twice(5)
【例011】备份程序
代码如下:
#!/usr/bin/env python
import os,time
source = [‘/home/test/c’,’/home/test/shell’] #源文件目录
target_dir = ‘/home/test/python’ #目标文件目录
today = target_dir + time.strftime(‘%y%m%d’) #
now = time.strftime(‘%h%m%s’)
if not os.path.exists(today): #判断目录是否存在
os.mkdir(today) #不存在的话则新建
print ‘successfully created directory’, today
target = today + os.sep + now + ‘.zip’ #target文件格式
zip_cmd = “zip -qr ‘%s’ %s” % (target, ‘ ‘.join(source)) #-q:安静模式 -r递归模式
#等价于 zip -qr /home/test/python20141202/142151.zip /home/test/c /home/test/shell
if os.system(zip_cmd) == 0: #判断命令是否成功执行，成功执行，返回0
print ‘successful back to:’, target
else: #失败的话，打印信息
print ‘backup failed.’
加comment的版本
代码如下:
#!/usr/bin/env python
import os,time
source = [‘/home/test/c’,’/home/test/shell’]
target_dir = ‘/home/test/python’
today = target_dir + time.strftime(‘%y%m%d’)
now = time.strftime(‘%h%m%s’)
comment = raw_input(‘enter comments here–>’) #要输入的comment
if len(comment) == 0: #如果没有comment
target = today + os.sep + now + ‘.zip’ #按照上面的操作执行
else:
target = today + os.sep + now + ‘_’ + comment.replace(‘ ‘,’_’) + ‘.zip’
#如果有comment,
if not os.path.exists(today):
os.mkdir(today)
print ‘the backup directory created!’, today
zip_command = “zip -qr ‘%s’ %s” % (target, ‘ ‘.join(source))
if os.system(zip_command) == 0:
print ‘scuccessful backup to’, target
else:
print ‘the backup failed’
输出结果 ：
代码如下:
# python backup_ver4.py
enter comments here–>add new example
the backup directory created! /home/test/python20141202
scuccessful backup to /home/test/python20141202/145130_add_new_example.zip
【例012】将二进制数转为10进制数
代码如下:
def func(b):
i = 0
while b:
i = i * 2 + (ord(b[0])-ord(‘0’))
b = b[1:]
return i
b = raw_input(‘enter binary here:’)
print func(b)
【例013】将列表中排除重复项并将重复的项找出
代码如下:
def find_duplicate(lst):
tmp = [] #临时变量，存放排除后的列表
for item in lst:
if not item in tmp: #将不在tmp变量找出
tmp.append(item)
else:
print ‘the duplicate item is:’, item
print ‘after remove the duplicate item:’,
return tmp
if __name__==’__main__’:
test = input(“enter list here:”) #input技巧
print find_duplicate(test)
>>>
enter list here:[2,1,4,2]
the duplicate item is: 2
after remove the duplicate item: [2, 1, 4]
【例014】用python中列表中append()，pop()函数实现简单的堆栈方法:后进先出
代码如下:
l = []
l.append(1)
l.append(2)
l.append(3)
print l
print l.pop()
print l.pop()
print l.pop()
【例015】对列表中的单词按首字母排序
代码如下:
>>> words = [‘apple’,’bat’,’bar’,’book’,’atom’]
>>> tmp = {} #建个空字典
>>> for word in words:
letter = word[0] #作为字典中的键
if letter not in tmp: #判断首字母是否存在于字典
tmp[letter] = [word] #注意要添加[],很关键
else:
tmp[letter].append(word) #如果键已经存在，值列表添加
>>> tmp
{‘a’: [‘apple’, ‘atom’], ‘b’: [‘bat’, ‘bar’, ‘book’]}
【例016】对文件进行整理（除空格、tab键、除#!&?等键），假如文本文件全为人名，并让首字母大写
代码如下:
john black
jerry!
&alice
tom#
south carolina###
mr smith?
代码及输出结果如下:
代码如下:
import re
def clean(strings):
result = []
for value in strings:
value = value.strip()
value = re.sub(‘[#!&?]’,”,value)
value = value.title()
result.append(value)
return result
with open(‘data.txt’,’a+’) as myfile:
lines = myfile.readlines()
for line in clean(lines):
print line
>>>
john black
jerry
alice
tom
south carolina
mr smith
【例017】用while循环来判断某个数是否是质数
代码如下:
y = input(‘enter a integer here:’)
x = y / 2
while x > 1:
if y % x == 0:
print y, ‘has factor’, x
break
x -= 1
else:
print y, ‘is prime’
【例018】用while实现搜索某个字符串的功能
代码如下:
names = [‘tom’,’alice’,’wendy’,’jerry’,’bob’,’smith’]
while names:
if names[0] == ‘jerry’:
print ‘hi,’, names[0]
break
names = names[1:]
else:
print ‘not found!’
【例019】对嵌套的序列进行处理
代码如下:
>>> t = ((1,2),(3,4),(5,6))
>>> for (a,b) in t:
… print a+100, b+200
…
101 202
103 204
105 206
【例020】用for循环实现查找
代码如下:
source = [‘sting’,(3,4),100,0.1,[1,2]]
tests = [(3,4),3.14]
for t in tests: #先是遍历小循环
for s in source: #再遍历外层循环
if s == t:
print t, ‘found it! ‘
break
else: #else语句的位置非常关键，
print t, ‘not found!’
等价于下面这种方式
代码如下:
source = [‘sting’,(3,4),100,0.1,[1,2]]
tests = [(3,4),100,3.14]
for t in tests:
if t in source:
print t, ‘found it.’
else:
print t, ‘not found.’
【例021】用for循环来收集两个序列中相同的部分
代码如下:
seq1 = ‘spam’
seq2 = ‘suck’
res = []
for s1 in seq1:
if s1 in seq2:
res.append(s1)
print res
【例022】隔个取出字符串
代码如下:
s = ‘abcdefghijklmn’
for i in range(0,len(s),2):
print s[i],
#或者
print s[::2]
【例023】两个列表，列表中每个元素加100，然后与l1中对应元素相乘，形成列表，再对列表求和
代码如下:
l1 = [1,2,3,4]
l2 = [5,6,7,8] #l2每个元素加一百,105,106,107
#(5+100)*1 + (6+100)*2 + (100+7)*3 + (100+8)*4
# 合计: 1070
l3 = [x+100 for x in l2]
l4 = []
for (x,y) in zip(l1,l3):
l4.append(x*y)
print sum(l4)
#或者用下面精简方式，只是刚看到有点头痛!
print sum([x*y for x,y in [t for t in zip(l1,[x+100 for x in l2])]])
【例024】对列表进行，合并，去重，取交集等操作
代码如下:
def func(seq1, seq2=none, opra=none):
res = []
if opra == ‘-‘:
for item1 in seq1:
if item1 not in seq2:
res.append(item1)
elif opra == ‘&’:
for item1 in seq1:
if item1 in seq2:
res.append(item1)
elif opra == ‘|’:
tmp = seq1[:]
for item1 in seq2:
if item1 not in seq1:
tmp.append(item1)
return tmp
elif opra == ‘^’:
for i in seq1:
if i not in seq2:
res.append(i)
for i in seq2:
if i not in seq1:
res.append(i)
return res
else:
print ‘need list as input!’
return res
l1 = [1,2,3,4]
l2 = [3,4,5,6]
print ‘[l1 – l2]:’,func(l1,l2,’-‘)
print ‘[l1 & l2]:’,func(l1,l2,’&’)
print ‘[l1 | l2]:’,func(l1,l2,’|’)
print ‘[l1 ^ l2]:’,func(l1,l2,’^’)
def list_remove(seq):
res = []
for i in seq:
if i not in res:
res.append(i)
return res
l1 = [3,1,2,3,8]
print list_remove(l1)
def find_duplicate(seq):
res = []
for i in range(len(seq)):
if seq.count(seq[i]) >= 2:
print ‘found %s’% seq[i], ‘the index is:’, i
res.append(seq[i])
return res
l1 = [3,1,2,3,8]
print find_duplicate(l1)
结果如下:
代码如下:
>>>
[l1 – l2]: [1, 2]
[l1 & l2]: [3, 4]
[l1 | l2]: [1, 2, 3, 4, 5, 6]
[l1 ^ l2]: [1, 2, 5, 6]
[3, 1, 2, 8]
found 3 the index is: 0
found 3 the index is: 3
[3, 3]
【例025】通过函数改变全局变量的三种方式
代码如下:
var = 99
def local():
var = 0
def glob1():
global var
var += 1
def glob2():
var = 0
import learn
learn.var += 1
def glob3():
var = 0
import sys
glob = sys.modules[‘learn’]
glob.var += 1
def test():
print var
local();glob1();glob2();glob3()
print var
【例026】求range(10)中每个元素的立方
代码如下:
def func():
res = []
for i in range(10):
res.append(lambda x, i=i: i ** x) #i=i这是关键，否则i默认记忆最后一个值:9
return res
>>> res = func()
>>> for i in range(10):
res[i](3)
0
1
8
27
64
125
216
343
512
729
【例027】求最小值
代码如下:
def min1(*args):
mini = args[0]
for arg in args[1:]:
if arg < mini:
mini = arg
return mini
def min2(first,*rest):
mini = first
for arg in rest:
if arg < first:
mini = arg
return mini
def min3(*args):
res = list(args)
res.sort()
return res[0]
print min1('c','a','b')
print min2(3,1,4)
print min3(1,'a',78,'c')
def func(test, *args):
res = args[0]
for arg in args[1:]:
if test(arg, res):
res = arg
return res
def lessthan(x, y): return x < y
def morethan(x, y): return x > y
print func(lessthan, 4,3,1,2,9)
print func(morethan, 4,3,1,2,9)
【例028】求多个集合的交集及合集
代码如下:
def intersect(*args):
res = []
for x in args[0]:
for other in args[1:]:
if x not in other:
break
else:
res.append(x)
return set(res) #去除重复的部分
print intersect(‘spam’,’scam’,’slam’)
def union(*args):
res = []
for seq in args:
for item in seq:
if not item in res:
res.append(item)
return res
print union(‘sa’,’sb’,’sc’)
def intersect(*args):
res = []
for x in args[0]:
for other in args[1:]:
if x not in other:
break
else:
res.append(x)
#为了交互[‘s’,’s’,’a’,’a’,’m’,’m’]
tmp = []
[tmp.append(i) for i in res if i not in tmp]
return tmp
print intersect(‘scam’,’spam’,’slam’)
【例029】字典的拷贝及添加
代码如下:
def copydict(old):
new = {}
for key in old:
new[key] = old[key]
return new
def adddict(d1,d2):
new = {}
for key in d1.keys():
new[key] = d1[key]
for key in d2:
new[key] = d2[key]
return new
【例030】求质数
代码如下:
def isprime(y):
if y < 1:
print y, 'not prime'
else:
x = y // 2
while x>1:
if y % x == 0:
print y, ‘has factor’, x
break
x -= 1
else:
print y, ‘is prime!’
【例031】比较多个值的大小
代码如下:
def min_max(func,*args):
res = args[0]
for arg in args[1:]:
if func(arg,res):
res = arg
return res
def min_func(x,y): return x < y def max_func(x,y): return x > y
if __name__==’__main__’:
print “the min value is:”, min_max(min_func,4,3,2,1,7,6,9)
print “the max value is:”, min_max(max_func,4,3,2,1,7,6,9)
# 输出结果:
>>>
the min value is: 1
the max value is: 9
【例032】写一个小函数实现内置函数dir的功能
代码如下:
#filename: mydir.py
tag = 1
def listing(module):
if tag:
print ‘-‘*30
print ‘name:’, module.__name__,’file:’, module.__file__
print ‘-‘*30
count = 0
for attr in module.__dict__.keys():
if attr[0:2] == ‘__’:
print ‘%02d) %s’ % (count, attr)
else:
print getattr(module,attr)
count = count + 1
if tag:
print ‘-‘*30
print module.__name__, ‘has %d names.’ % count
print ‘-‘*30
if __name__==’__main__’:
import mydir
listing(mydir)
【例033】求分数平均值
代码如下:
””’filename: grades.txt 求该文件中第二列的平均值
jerry 78
alice 45
wendy 96
tom 56
bob 85
”’
temp = []
for line in open(‘grades.txt’):
a = line.strip().split()
if a:
temp.append(a[1])
#[’78’, ’45’, ’96’, ’56’, ’85’]
total = 0
for i in temp:
total += int(i)
print ‘the total grade is:’, total, ‘the average is:’, total/len(tmp)
【例034】一个实际类的例子
代码如下:
class genericdisplay:
def gatherattrs(self):
attrs = ‘\n’
for key in self.__dict__:
attrs += ‘\t%s=%s\n’ % (key, self.__dict__[key])
return attrs
def __str__(self):
return ” % (self.__class__.__name__, self.gatherattrs())
class person(genericdisplay):
def __init__(self, name, age):
self.name = name
self.age = age
def lastname(self):
return self.name.split()[-1]
def birthday(self):
self.age += 1
class employee(person):
def __init__(self, name, age, job=none, pay=0):
person.__init__(self, name, age)
self.job = job
self.pay = pay
def birthday(self):
self.age += 2
def giveraise(self, percent):
self.pay *= (1.0 + percent)
if __name__ == ‘__main__’:
bob = person(‘bob smith’, 40)
print bob
print bob.lastname()
bob.birthday()
print bob
sue = employee(‘sue jones’, 44, job=’dev’, pay=100000)
print sue
print sue.lastname
sue.birthday()
sue.giveraise(.10)
print sue
【例035】根据给定的年月日以数字方式打印出日期(february 27th, 2015)
代码如下:
# coding = utf-8
#根据给定的年月日以数字形式打印出日期
months = [
‘january’ ,
‘february’,
‘march’ ,
‘april’ ,
‘may’ ,
‘june’ ,
‘july’ ,
‘august’ ,
‘september’,
‘october’ ,
‘november’ ,
‘december’
]
#以1~31的数字作为结尾的列表
endings = [‘st’,’nd’,’rd’] + 17 * [‘th’] + \
[‘st’,’nd’,’rd’] + 07 * [‘th’] + \
[‘st’]
year = raw_input(‘year: ‘)
month = raw_input(‘month(1-12): ‘)
day = raw_input(‘day(1-31): ‘)
month_number = int(month)
day_number = int(day)
#月份和天数减1来获得正确的索引
month_name = months[month_number – 1]
ordinal = day + endings[day_number – 1]
print month_name + ‘ ‘ + ordinal + ‘, ‘ + year
#输出结果
>>>
year: 2015
month(1-12): 2
day(1-31): 27
february 27th, 2015
【例036】在居中的盒子里打印一条语句
代码如下:
sentence = raw_input(“sentence: “)
screen_width = 80
text_width = len(sentence)
box_width = text_width + 6
left_margin = (screen_width – box_width) // 2
print
print ‘ ‘*left_margin + ‘+’ + ‘-‘*(box_width-4) + ‘+’
print ‘ ‘*left_margin + ‘| ‘ + ‘ ‘*(text_width) +’ |’
print ‘ ‘*left_margin + ‘| ‘ + sentence +’ |’
print ‘ ‘*left_margin + ‘| ‘ + ‘ ‘*(text_width) +’ |’
print ‘ ‘*left_margin + ‘+’ + ‘-‘*(box_width-4) + ‘+’
print
#输出结果
>>>
sentence: welcome to beijing!
+———————+
| |
| welcome to beijing! |
| |
+———————+
【例037】简单小数据库验证
代码如下:
database = [
[‘bob’, ‘1234’],
[‘tom’, ‘2345’],
[‘foo’, ‘1478’]
]
usr = raw_input(‘enter username: ‘)
pwd = raw_input(‘enter password: ‘)
if [usr, pwd] in database:
print ‘access granted!’
else:
print ‘access deny!’
【例038】使用给定的宽度打印格式化后的价格列表
代码如下:
width = input(‘please enter width: ‘)
price_width = 10
item_width = width – price_width
header_format = ‘%-*s%*s’
format = ‘%-*s%*.2f’
print ‘=’ * width
print header_format % (item_width, ‘item’, price_width, ‘price’)
print ‘-‘ * width
print format % (item_width, ‘apples’, price_width, 0.4)
print format % (item_width, ‘sweets’, price_width, 0.5)
print format % (item_width, ‘pepper’, price_width, 12.94)
print format % (item_width, ‘tender’, price_width, 42)
print ‘-‘ * width
输出格式:
代码如下:
>>>
please enter width: 30
==============================
item price
——————————
apples 0.40
sweets 0.50
pepper 12.94
tender 42.00
——————————
【例039】遍历两个对应列表
代码如下:
names = [‘alice’, ‘bob’ , ‘cherry’, ‘david’]
numbers = [‘0000’ , ‘1111’, ‘2222’ , ‘3333’ ]
for index,name in enumerate(names):
print ‘%-7s=> %s’ % (name, numbers[index])
#输出结果
>>>
alice => 0000
bob => 1111
cherry => 2222
david => 3333
当然也可以采用如下通常的做法:
代码如下:
names = [‘alice’,’bob’, ‘john’, ‘fred’]
ages = [27, 23, 31, 29]
for i in range(len(ages)):
print names[i],’ is ‘, ages[i], ‘ years old!’
#输出结果:
>>>
alice is 27 years old!
bob is 23 years old!
john is 31 years old!
fred is 29 years old!
【例040】对存储在小字典中数据进行查询
代码如下:
peoples = {
‘alice’:{
‘phone’ : ‘0948’,
‘address’ : ‘aaaa’
},
‘wendy’:{
‘phone’ : ‘4562’,
‘address’ : ‘bbbb’
},
‘david’:{
‘phone’ : ‘4562’,
‘address’ : ‘bbbb’
}
}
#字典使用人名作为键。每个人用另外一个字典来表示，其键’phone’和’addr’分别表示他们的电话号码和地址
labels = {
‘phone’ : ‘phone number’,
‘address’ : ‘address’
}
#针对电话号码和地址使用描述性标签，会在打印输出时用到。
key = ”
name = raw_input(‘name: ‘)
if name in peoples:
request = raw_input(‘enter (p) or (a): ‘)
if request == ‘p’:
key = ‘phone’
elif request == ‘a’:
key = ‘address’
else:
print ‘please input p(phone) an a(address)!’
print “%s’s %s is %s” % (name, labels[key],peoples[name][key])
else:
print ‘not found!’
或者使用字典的get()方法，更好些。完整代码如下:
代码如下:
#字典使用人名作为键。每个人用另外一个字典来表示，其键’phone’和’addr’分别表示他们的电话号码和地址
peoples = {
‘alice’:{
‘phone’ : ‘0948’,
‘address’ : ‘aaaa’
},
‘wendy’:{
‘phone’ : ‘4562’,
‘address’ : ‘bbbb’
},
‘david’:{
‘phone’ : ‘4562’,
‘address’ : ‘bbbb’
}
}
#针对电话号码和地址使用描述性标签，会在打印输出时用到。
labels = {
‘phone’ : ‘phone number’,
‘addr’ : ‘address’
}
name = raw_input(‘name: ‘)
#查找电话号码还是地址?
request = raw_input(‘phone number (p) or address (a)? ‘)
#查找正确的键
key = request #如果请求即不是p也不是a
if request == ‘p’: key = ‘phone’
if request == ‘a’: key = ‘addr’
#使用get()函数提供默认值
person = peoples.get(name,{})
label = labels.get(key, key)
result = person.get(key, ‘not available’)
print “%s’s %s is %s.” % (name, label, result)
【例041】字典格式化字符串例子
代码如下:
template=””’
%(title)s
%(text)s
”’
data = {‘title’:’my home page’,’text’:’welcome to my home page!’}
print template % data
#输出结果:
>>>
my home page
welcome to my home page!
【例042】需找100以内的最大平方数
代码如下:
from math import sqrt
#从100开始往下找，找到即停止，最大为: 81
for n in range(99, 0, -1):
root = sqrt(n)
if root == int(root):
print n
break
【例043】用while/true, break控制输入
代码如下:
while true: #一直进行下去，除非break
word = raw_input(‘please enter a word: ‘)
if not word: break #输入为空的话，中断循环
print ‘the word was: ‘ + word
【例044】将两个列表中首字母相同的提取出来
代码如下:
#将两个列表中首字母相同的罗列在一起
girls = [‘alice’, ‘bernice’, ‘clarice’]
boys = [‘chris’, ‘arnold’, ‘bob’]
#列表推导:
print [b+’+’+g for b in boys for g in girls if b[0] == g[0]]
#输出结果:
>>>
[‘chris+clarice’, ‘arnold+alice’, ‘bob+bernice’]
【例045】斐波那契数列求指定数字的列表
代码如下:
def fibs(x):
fibs = [0, 1] # 初始值
for i in range(x):
# fibs[-2]+fibs[-1]：最新一个值是前面两个值之和
# 并用append方法将其添加在后面
fibs.append(fibs[-2]+fibs[-1])
print fibs
if __name__==’__main__’:
num = input(‘how many fibonacci numbers do you want? ‘)
fibs(num)
或者用普通方法实现:
代码如下:
>>> def fib(max):
n, a, b = 0, 0, 1
tmp_list = []
while n < max:
tmp_list.append(a)
a, b = b, a+b
n += 1
return tmp_list
>>> fib(8)
[0, 1, 1, 2, 3, 5, 8, 13]
【例046】写一个自定义列表类，让它支持尽可能多的支持操作符号
代码如下:
class mylist:
def __init__(self, start):
self.wrapped = [] # make sure it’s a list here
for x in start:
self.wrapped.append(x)
def __add__(self, other):
return mylist(self.wrapped + other)
def __mul__(self, time):
return mylist(self.wrapped * time)
def __getitem__(self, offset):
return self.wrapped[offset]
def __len__(self):
return len(self.wrapped)
def __getslice__(self, low, high):
return mylist(self.wrapped[low:high])
def append(self, node):
self.wrapped.append(node)
def __getattr__(self, name): # other members: sort/reverse/etc
return getattr(self.wrapped, name)
def __repr__(self):
return repr(self.wrapped)
if __name__ == ‘__main__’:
x = mylist(‘spam’)
print x
print x