Python是比较热的语言,个人兴趣参考官方文档:https://docs.python.org/2/tut…
边看边翻译了一下(后面会持续更新),有兴趣的可以看看。
Python具有高级的数据结构,能高效地面向对象编程。它的优雅的语法、动态类型、解释属性使它能快速地在大部分平台开发应用程序。它的第三方包、工具和库都可以在这里找到:https://www.python.org/。
Python很容易通过C/C++函数或数据类型进行扩展。写扩展参看:扩展指导, C/C++的Python API
更多文档参看Python标准库,Python的API
通过这个入门教程,你将学习到Pyton的一些常用特性和标准库的一些方法或模块。
写在前面
对于每天在电脑面前工作的人来说,可能你需要做一些自动化的工作,比如批量替换,查找更改等,或者你想写一些界面程序,游戏等。
而对于专业的软件开发人员来说,通过C/C++/Java库去开发
、测试、编译等又太繁琐了。
这时候,Python是最佳的选择。
你可以写一些shell脚本或者bat脚本去移动文件或者修改数据,但不是很适合写界面程序或者游戏。C/C++/Java又太繁琐了。而Python比较适合快速的在各个平台(windows, Mac, Unix)完成你要的工作。
Python是一门真正的编程语言,它有高级的数据结构,比如可灵活操作的数组和字典。
Python是模块化的,它的标准库里面有你可用的一些模块,这些模块提供了比如文件I/O,sockets等功能。
Python可以写出比C/C++/Java更简洁的程序,原因有三:
1 有高级的数据结构
2 通过缩进进行区分声明块而不是括号
3 不需要变量或者参数声明
Python是可扩展的。你可以把Python解释器嵌入到C程序中。
使用Python解释器
运行python解释器
方式1:
Python解释器在linux下一般安装在/usr/local/bin/python目录下,切换到该目录下,输入以下命令可以运行python解释器
python
windows下一般安装在C:Python27目录下,win+r快捷键,然后输入一下cmd,打开dos界面,输入以下命令,设置环境变量:
set path=%path%;C:\python27
则任意目录下,输入python命令即可打开python解释器
方式2:
python -c command [arg] ..
因为命令行可能有一些特殊字符或者空白,最好用单引号引起来。
退出python解释器:
Unix下在命令行界面输入快捷键:Control-D, Windows下输入Control-Z。
或者输入:
quit()
调用python模块(模块也就是python源文件):
python -m module [arg] ...
进入交互命令模式:
python -i ...
参数传递
命令行的参数会赋值给sys模块的argv变量。可以通过import sys访问参数。argv的长度至少有1。当没有参数的时候,sys.argv[0]是一个空串。当脚本的名字为”-“,则sys.argv[0]是”-“,当用了-c命令,则sys.argv[0]的值为”-c”。当用了-m,sys.argv[0]的值为模块的名字。-c和-m后面的参数,python解释器不会处理。
交互模式
多行模式前面是… 单行是>>>
>>> the_world_is_flat = 1
>>> if the_world_is_flat:
... print "Be careful not to fall off!"
...
解释器和环境
设置代码编码
一般情况是不用设置的 默认为utf-8
#!/usr/bin/env python
# -*- coding: cp-1252 -*-
Python介绍
开头标识注释,>>>和…开头标识python语句
>>>
>>> #这是注释
... a = 1;#这是注释
>>> print a
1
把python当做计算器
数字
>>> 2 + 2
4
>>> 50 - 5*6
20
>>> (50 - 5.0*6) / 4
5.0
>>> 8 / 5.0
1.6
这里2是int 5.0是float,/的结果是什么类型是根据参与计算的两个数,如果有一个数是float则返回float类型。
//操作符是向下取数,小数位为0。
>>> 12//7.0
1.0
>>>
%是求余
**是多次方
>>> 5**2
25
>>>
声明变量n=12
如果使用一个未声明的变量会报错
>>> n
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'n' is not defined
>>>
多项式计算,会自动进行数据类型的转换:int和float一起计算,int会自动转为float
交互模式下,最后一个打印的变量会赋值给_
>>> tax = 12.5 / 100
>>> price = 100.50
>>> price * tax
12.5625
>>> price + _
113.0625
>>> round(_, 2)
113.06
_是只读的,不能被赋值。
字符串
单引号或者双引号里表示字符串,用来转义
如果不想要转义:字符串前加一个r
>>> print 'C:\some\name' # here \n means newline!
C:\some
ame
>>> print r'C:\some\name' # note the r before the quote
C:\some\name
多行字符串:三个”””或者”’
print """\
Usage: thingy [OPTIONS]
-h Display this usage message
-H hostname Hostname to connect to
"""
标识去掉换行,没有输出是这样的:
>>> print """
... aef
... asdf
... """
aef
asdf
字符串拼接:+ 字符串重复:*
>>> "un"*2 +" awef"
'unun awef'
>>>
自动拼接:
>>> 'Py' 'thon'
'Python'
获取字符串的单个字符
>>> a = "python"
>>> a[0]
'p'
负数标识从尾部开始读取: -0等于0 最后一个字符是-1
>>> a = "python"
>>> a[-1]
'n'
>>>
取区间:
>>> a = "python"
>>> a[0:2]
'py'
>>> a[2:]
'thon'
>>> a[:4]
'pyth'
>>> a[-2:]
'on'
>>>
越界访问数组会报错:
>>> word[42] # the word only has 6 characters
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: string index out of range
但是取不存在的区间不会报错:
>>> a[-2:45]
'on'
>>>
字符串无法被修改:
>>> word[0] = 'J'
...
TypeError: 'str' object does not support item assignment
>>> word[2:] = 'py'
...
TypeError: 'str' object does not support item assignment
unicode字符串
支持unicode字符串:字符串前加u
>>> u'Hello World !'
u'Hello World !'
>>> u'Hello\u0020World !'
u'Hello World !'
0x0020标识空格
支持原始模式: 字符串前面加入ur
python的默认编码方式是:ASCII码,如果Unicode字符串被打印或者写到文件或者是str()方法转化都会默认转为ASCII码,如果字符串不在0-127范围就会报错
>>> u"abc"
u'abc'
>>> str(u"abc")
'abc'
>>> u"äöü"
u'\xe4\xf6\xfc'
>>> str(u"äöü")
Traceback (most recent call last):
File "<stdin>", line 1, in ?
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-2: ordinal not in range(128)
转换为特定编码:方法的参数为小写
>>> u"äöü".encode('utf-8')
'\xc3\xa4\xc3\xb6\xc3\xbc'
数组
定义一个数组
>>> squares = [1, 4, 9, 16, 25]
>>> squares
[1, 4, 9, 16, 25]
获取数组内元素
>>> squares[0] # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:] # slicing returns a new list 例子三
[9, 16, 25]
获取数组内片段,比如上面例子三,会返回一个新的数组拷贝,原数组不会发生改变
数组合并:
>>> squares + [36, 49, 64, 81, 100]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
字符串的内容是不能被更改的,而数组是可以被更改的:
>>> cubes = [1, 8, 27, 65, 125] # something's wrong here
>>> 4 ** 3 # the cube of 4 is 64, not 65!
64
>>> cubes[3] = 64 # replace the wrong value
>>> cubes
[1, 8, 27, 64, 125]
给数组添加元素:
>>> cubes.append(216) # add the cube of 6
>>> cubes.append(7 ** 3) # and the cube of 7
>>> cubes
[1, 8, 27, 64, 125, 216, 343]
可以赋值给截取的数组:
>>> letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> letters
['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> # replace some values
>>> letters[2:5] = ['C', 'D', 'E']
>>> letters
['a', 'b', 'C', 'D', 'E', 'f', 'g']
>>> # now remove them
>>> letters[2:5] = []
>>> letters
['a', 'b', 'f', 'g']
>>> # clear the list by replacing all the elements with an empty list
>>> letters[:] = []
>>> letters
[]
获取数组的长度:
>>> letters = ['a', 'b', 'c', 'd']
>>> len(letters)
4
数组的元素也可以是一个数组:
>>> a = ['a', 'b', 'c']
>>> n = [1, 2, 3]
>>> x = [a, n]
>>> x
[['a', 'b', 'c'], [1, 2, 3]]
>>> x[0]
['a', 'b', 'c']
>>> x[0][1]
'b'
终于开始编程了!
如何实现一个斐波那契:
>>> # 这是一个注释
... a, b = 0, 1 #分别给a赋值为0 b赋值为1
>>> while b < 10:#这是一个循环
... print b #打印b的值(并且这里的代码前面有空格(也就是行缩进))
... a, b = b, a+b #a赋值为b,b赋值为a+b的和
...
1
1
2
3
5
8
之前说过,行缩进标识接下来是一个代码块。
print方法,可以控制格式,比如增加空格:
>>> i = 256*256
>>> print 'The value of i is', i
The value of i is 65536
在print语句最后加一个逗号,避免打印结果换行:
>>> a, b = 0, 1
>>> while b < 1000:
... print b,
... a, b = b, a+b
...
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987
控制流
if语句
>>> x = int(raw_input("Please enter an integer: "))
Please enter an integer: 42
>>> if x < 0: #冒号可以开启多行模式
... x = 0
... print 'Negative changed to zero'
... elif x == 0:
... print 'Zero'
... elif x == 1:
... print 'Single'
... else:
... print 'More'
...
if…elif..else(不是必须的)…
for
Python的for可以遍历数组和字符串(这个和C语言的for语句有略微不同)
>>> # Measure some strings:
... words = ['cat', 'window', 'defenestrate']
>>> for w in words:
... print w, len(w)
...
cat 3
window 6
defenestrate 12
在循环内修改一个数组:首先通过截取数组的方法对原数组进行拷贝(这个知识点之前有提过)
>>> for w in words[:]: # words[:]可以对原数组进行拷贝
... if len(w) > 6:
... words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']
range()函数
range函数能根据算法创建一个数组
>>> range(5, 10) #创建所有元素为5到10区间并递增的数组
[5, 6, 7, 8, 9]
>>> range(0, 10, 3)#递增3
[0, 3, 6, 9]
>>> range(-10, -100, -30)#递减30
[-10, -40, -70]
遍历数组的索引:
>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for i in range(len(a)):
... print i, a[i]
...
0 Mary
1 had
2 a
3 little
4 lamb
退出循环
break语句执行会退出里层的for循环;continue会跳过后面语句的执行(和C语言用法一样)。
>>> for n in range(2, 10):
... for x in range(2, n):
... if n % x == 0:
... print n, 'equals', x, '*', n/x
... break
... else:
... # loop fell through without finding a factor
... print n, 'is a prime number'
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3
pass语句
pass语句不会做任何事,只是用来占位用的
>>> class MyEmptyClass:
... pass
...
>>> def initlog(*args):
... pass # Remember to implement this!
...
定义函数和调用函数
>>> def fib(n): # def关键字标识定义函数,这里函数名为fib
... """Print a Fibonacci series up to n.""" #
... a, b = 0, 1
... while a < n:
... print a,
... a, b = b, a+b
...
>>> # Now call the function we just defined:
... fib(2000)
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
注意函数体要代码要缩进
函数可以被赋值(fib会被加入符号表):
>>> fib
<function fib at 10042ed0>
>>> f = fib # f也会被加入符号表
>>> f(100)
0 1 1 2 3 5 8 13 21 34 55 89
即便函数没有return,也会返回一个None
>>> fib(0)
>>> print fib(0)
None
return后面没有跟任何东西也是返回None
>>> def fib2(n): # return Fibonacci series up to n
... result = []
... a, b = 0, 1
... while a < n:
... result.append(a) # 这里是调用数组的append方法
... a, b = b, a+b
... return result
...
>>> f100 = fib2(100) # call it
>>> f100 # write the result
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
定义带参数的函数
参数带默认值:retries的默认值为4
def ask_ok(prompt, retries=4, complaint='Yes or no, please!'):
while True: # True是关键字
ok = raw_input(prompt) #raw_input是内置的函数,用于IO输入
if ok in ('y', 'ye', 'yes'):
return True
if ok in ('n', 'no', 'nop', 'nope'):
return False
retries = retries - 1
if retries < 0:
raise IOError('refusenik user') # raise是关键字 抛出异常
print complaint
默认值可以为变量:i是一个变量
i = 5
def f(arg=i):
print arg
i = 6
f()
默认参数如果是一个可变的对象,会被赋值多次:
def f(a, L=[]):
L.append(a)
return L
print f(1)
print f(2)
print f(3)
会打印出:
[1]
[1, 2]
[1, 2, 3]
如果你不想L被改变,你可以这么做:
def f(a, L=None):
if L is None:
L = []
L.append(a)
return L
如果只接受一个参数,但是传递了两个参数会报错:
>>> def function(a):
... pass
...
>>> function(0, a=0)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: function() got multiple values for keyword argument 'a'
**kewords接收字典参数:
def cheeseshop(kind, *arguments, **keywords):
print "-- Do you have any", kind, "?"
print "-- I'm sorry, we're all out of", kind
for arg in arguments:
print arg
print "-" * 40
keys = sorted(keywords.keys()) #按字典顺序
for kw in keys:
print kw, ":", keywords[kw]
*arg接受不确定个数的参数:
def write_multiple_items(file, separator, *args):
file.write(separator.join(args))
自动解析参数:
>>> range(3, 6) # 正常情况调用方式
[3, 4, 5]
>>> args = [3, 6]
>>> range(*args) # 从一个数组里解析参数
[3, 4, 5]
>>> def parrot(voltage, state='a stiff', action='voom'):
... print "-- This parrot wouldn't", action,
... print "if you put", voltage, "volts through it.",
... print "E's", state, "!"
...
>>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}
>>> parrot(**d)
-- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised !
文档字符串:
>>> def my_function():
... """Do nothing, but document it.
...
... No, really, it doesn't do anything.
... """
... pass
...
>>> print my_function.__doc__
Do nothing, but document it.
No, really, it doesn't do anything.
Lambda表达式一个匿名函数,lambda a, b: a+b. a和b是两个参数,结果返回a和b的和:
>>> def make_incrementor(n):
... return lambda x: x + n
...
>>> f = make_incrementor(42)
>>> f(0)
42
>>> f(1)
43
lambda也可以作为参数传递:
>>> pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
>>> pairs.sort(key=lambda pair: pair[1])
>>> pairs
[(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]
编码格式建议
不用Tab缩进,用4倍空格缩进
必要时换行(避免单行超出79个字符)
用空格区分函数或者类或者函数内部的一大段代码
代码前面加上必要的注释
用文档字符串
操作符liagn两边或者逗号后面必须空格
函数采用lower_case_width_underscore方式命令,类用驼峰(CanekCase)方式命名;总是用self当作类的第一个方法的参数
不要用特殊的编码格式(ASCII是兼容所有的)
数据结构
数组
python数据默认有一些常用方法:比如append, extend, insert等等
作为堆栈使用
>>> stack = [3, 4, 5]
>>> stack.append(6)
>>> stack.append(7)
>>> stack
[3, 4, 5, 6, 7]
>>> stack.pop()
7
>>> stack
[3, 4, 5, 6]
>>> stack.pop()
6
>>> stack.pop()
5
>>> stack
[3, 4]
作为队列使用
>>> from collections import deque
>>> queue = deque(["Eric", "John", "Michael"])
>>> queue.append("Terry") # Terry arrives
>>> queue.append("Graham") # Graham arrives
>>> queue.popleft() # The first to arrive now leaves
'Eric'
>>> queue.popleft() # The second to arrive now leaves
'John'
>>> queue # Remaining queue in order of arrival
deque(['Michael', 'Terry', 'Graham'])
一些常用的方法
filter(function, sequence) : 返回function的值为true的所有值
>>> def f(x): return x % 3 == 0 or x % 5 == 0
...
>>> filter(f, range(2, 25))
[3, 5, 6, 9, 10, 12, 15, 18, 20, 21, 24]
map(function, sequence): 返回处理后的值
>>> def cube(x): return x*x*x
...
>>> map(cube, range(1, 11))
[1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
传递两个数组: 分别从一个数组里取出一个数 返回相加后的结果
>>> seq = range(8)
>>> def add(x, y): return x+y
...
>>> map(add, seq, seq)
[0, 2, 4, 6, 8, 10, 12, 14]
reduce(function, sequence) :把数组的第一个和第二个参数想加的和和第三个数再加。。如果数组为空,会返回异常
>>> def add(x,y): return x+y
...
>>> reduce(add, range(1, 11))
55
reduce可以指定开始的第一个数的索引:
>>> def sum(seq):
... def add(x,y): return x+y
... return reduce(add, seq, 0)
...
>>> sum(range(1, 11))
55
>>> sum([])
0
创建数组的几种形式:
>>> squares = []
>>> for x in range(10):
... squares.append(x**2)
...
>>> squares
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
squares = [x**2 for x in range(10)]
squares = map(lambda x: x**2, range(10))
更复杂点的例子:x,y作为一个整体 必须加上括号
>>> [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]
[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]
更多例子:
>>> freshfruit = [' banana', ' loganberry ', 'passion fruit ']
>>> [weapon.strip() for weapon in freshfruit]
['banana', 'loganberry', 'passion fruit']
>>> [x, x**2 for x in range(6)]
File "<stdin>", line 1, in <module>
[x, x**2 for x in range(6)]
^
SyntaxError: invalid syntax
>>> # flatten a list using a listcomp with two 'for'
>>> vec = [[1,2,3], [4,5,6], [7,8,9]]
>>> [num for elem in vec for num in elem]
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> from math import pi
>>> [str(round(pi, i)) for i in range(1, 6)]
['3.1', '3.14', '3.142', '3.1416', '3.14159']
二维数组
>>> matrix = [
... [1, 2, 3, 4],
... [5, 6, 7, 8],
... [9, 10, 11, 12],
... ]
复杂点的例子:
>>> [[row[i] for row in matrix] for i in range(4)]
[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
相当于:
>>> transposed = []
>>> for i in range(4):
... transposed.append([row[i] for row in matrix])
...
>>> transposed
[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
删除数组内元素:del
>>> a = [-1, 1, 66.25, 333, 333, 1234.5]
>>> del a[0]
>>> a
[1, 66.25, 333, 333, 1234.5]
>>> del a[2:4]
>>> a
[1, 66.25, 1234.5]
>>> del a[:]
>>> a
[]
删除整个数组:
>>> del a
新类型:元组。
输入可以加括号,也可以不加。输出都是带括号的。
>>> t = 12345, 54321, 'hello!' # 输入 没加括号
>>> t[0]
12345
>>> t
(12345, 54321, 'hello!') # 输出 带括号
>>> # Tuples may be nested:
... u = t, (1, 2, 3, 4, 5)
>>> u
((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
>>> # 无法被修改
... t[0] = 88888
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> # 内部的元素可以是可变的类型 比如数组等
... v = ([1, 2, 3], [3, 2, 1])
>>> v
([1, 2, 3], [3, 2, 1])
空元组和只有一个元素的元组:
>>> empty = ()
>>> singleton = 'hello', # <-- note trailing comma
>>> len(empty)
0
>>> len(singleton)
1
>>> singleton
('hello',)
逆序元素:
>>> t = (12345, 54321, 'hello!')
>>> x, y, z = t
新的类型:集合
创建空集合:set()
>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> fruit = set(basket) # 创建集合
>>> fruit
set(['orange', 'pear', 'apple', 'banana'])
>>> 'orange' in fruit # 测试是否oranage是否是集合fruit内部
True
>>> 'crabgrass' in fruit
False
集合a, b 之间的交集 并集
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a # unique letters in a
set(['a', 'r', 'b', 'c', 'd'])
>>> a - b # letters in a but not in b
set(['r', 'd', 'b'])
>>> a | b # letters in either a or b
set(['a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'])
>>> a & b # letters in both a and b
set(['a', 'c'])
>>> a ^ b # letters in a or b but not both
set(['r', 'd', 'b', 'm', 'z', 'l'])
>>> a = {x for x in 'abracadabra' if x not in 'abc'}
>>> a
set(['r', 'd'])
新的类型:字典
字典是根据key索引的,而key数据类型可以为数字或者字符串,元组的元素都是不可变的,也可以作为key。数组不能作为key,因为数组可被修改
>>> tel = {'jack': 4098, 'sape': 4139}
>>> tel['guido'] = 4127
>>> tel
{'sape': 4139, 'guido': 4127, 'jack': 4098}
>>> tel['jack']
4098
>>> del tel['sape']
>>> tel['irv'] = 4127
>>> tel
{'guido': 4127, 'irv': 4127, 'jack': 4098}
>>> tel.keys()
['guido', 'irv', 'jack']
>>> 'guido' in tel
True
dict方法直接创建字典:
>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
{'sape': 4139, 'jack': 4098, 'guido': 4127}
>>> {x: x**2 for x in (2, 4, 6)}
{2: 4, 4: 16, 6: 36}
>>> dict(sape=4139, guido=4127, jack=4098)
{'sape': 4139, 'jack': 4098, 'guido': 4127}
遍历
通过enumerate方法
>>> for i, v in enumerate(['tic', 'tac', 'toe']):
... print i, v
...
0 tic
1 tac
2 toe
一次性遍历多个(这个特性不错。。
>>> questions = ['name', 'quest', 'favorite color']
>>> answers = ['lancelot', 'the holy grail', 'blue']
>>> for q, a in zip(questions, answers):
... print 'What is your {0}? It is {1}.'.format(q, a)
...
What is your name? It is lancelot.
What is your quest? It is the holy grail.
What is your favorite color? It is blue
逆序遍历:reversed
>>> for i in reversed(xrange(1,10,2)):
... print i
...
9
7
5
3
1
对数组排序(sorted方法),然后遍历:
>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> for f in sorted(set(basket)):
... print f
...
apple
banana
orange
pear
遍历字典的时候,获得key和value:
>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.iteritems():
... print k, v
...
gallahad the pure
robin the brave
遍历的时候改变一个数组:
>>> import math
>>> raw_data = [56.2, float('NaN'), 51.7, 55.3, 52.5, float('NaN'), 47.8]
>>> filtered_data = []
>>> for value in raw_data:
... if not math.isnan(value):
... filtered_data.append(value)
...
>>> filtered_data
[56.2, 51.7, 55.3, 52.5, 47.8]
更多条件语句
比较运算符:
in和not in判断是否在序列里面; is和is not用来比较两个对象是否是同一个对象;
比较可以链式: a < b == c 判断a小于b,并且b等于c
布尔操作符:and和or 优先级比比较运算符低 not优先级最高 or最低
布尔运算符,当一个满足条件不会继续下面的计算
比较结果可以被赋值:
>>> string1, string2, string3 = '', 'Trondheim', 'Hammer Dance'
>>> non_null = string1 or string2 or string3
>>> non_null
'Trondheim'
模块
退出解释器后,所有声明的函数或者变量都不存在了。所以我们需要创建一个python脚本,可持续地运行。每一个脚本文件称之为一个模块。
比如我们创建一个文件:fibo.py
# 这是一个模块
def fib(n): # 定义函数fib
a, b = 0, 1
while b < n:
print b,
a, b = b, a+b
def fib2(n): # 定义函数fib2
result = []
a, b = 0, 1
while b < n:
result.append(b)
a, b = b, a+b
return result
在解释器里面导入这个模块:
>>> import fibo
访问模块的函数:
>>> fibo.fib(1000)
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987
>>> fibo.fib2(100)
[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
>>> fibo.__name__
'fibo'
函数赋给一个变量
>>> fib = fibo.fib
>>> fib(500)
1 1 2 3 5 8 13 21 34 55 89 144 233 377
执行模块脚本
这样运行一个模块
python fibo.py <arguments>
和导入一个模块,并且把__name__设置为__main__是一样的:相当于把下面的代码放到模块的底部
if __name__ == "__main__":
import sys
fib(int(sys.argv[1]))
这样单纯导入是不会运行这个脚本的:
>>> import fibo
>>>
模块寻找路径
1 内置模块
2 搜索sys.path里面的所有目录
sys.path初始化的内容:
当前目录
PYTHONPATH (目录路径,它和环境变量的PATH语法一致)
Python安装路径
sys.path会被修改,当前目录优先于标准库路径。
编译后的Python文件
如果 spam.pyc(编译后的Python文件)和spam.py共存,会优先用编译后的文件。spam.pyc保存的编译时间和spam.py的修改时间不一致,则编译后的文件会被忽略(也就是用spam.py文件)。spam.pyc文件是平台独立的,也就是说能被各个平台共享。
标准模块
Python有自己的标准库。为了达到更底层的东西,有些模块已经内置到解析器中。而且有些内置模块依赖于环境,比如winreg模块只在window环境下提供。而一个值得关注的模块是:sys,它被内置到了每个Python解释器中。sys.ps1和sys.ps2表示Python的提示符
>>>import sys
>>>sys.ps1
'>>> '
>>> sys.ps2
'... '
>>> sys.ps1 = 'C> '
C> print 'Yuck!'
Yuck!
C>
sys.path的值是解释器的模块搜索路径。我们可以增加路径:
>>> import sys
>>> sys.path.append('/ufs/guido/lib/python')
dir()函数
dir()函数返回一个字符串的数组,它被用来表示一个模块定义了哪些名字
>>> import fibo, sys
>>> dir(fibo)
['__name__', 'fib', 'fib2']
>>> dir(sys)
['__displayhook__', '__doc__', '__excepthook__', '__name__', '__package__',
'__stderr__', '__stdin__', '__stdout__', '_clear_type_cache',
'_current_frames', '_getframe', '_mercurial', 'api_version', 'argv',
'builtin_module_names', 'byteorder', 'call_tracing', 'callstats',
'copyright', 'displayhook', 'dont_write_bytecode', 'exc_clear', 'exc_info',
'exc_traceback', 'exc_type', 'exc_value', 'excepthook', 'exec_prefix',
'executable', 'exit', 'flags', 'float_info', 'float_repr_style',
'getcheckinterval', 'getdefaultencoding', 'getdlopenflags',
'getfilesystemencoding', 'getobjects', 'getprofile', 'getrecursionlimit',
'getrefcount', 'getsizeof', 'gettotalrefcount', 'gettrace', 'hexversion',
'long_info', 'maxint', 'maxsize', 'maxunicode', 'meta_path', 'modules',
'path', 'path_hooks', 'path_importer_cache', 'platform', 'prefix', 'ps1',
'py3kwarning', 'setcheckinterval', 'setdlopenflags', 'setprofile',
'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout', 'subversion',
'version', 'version_info', 'warnoptions']
不带参数则返回当前你定义的模块函数变量名字
>>> a = [1, 2, 3, 4, 5]
>>> import fibo
>>> fib = fibo.fib
>>> dir()
['__builtins__', '__name__', '__package__', 'a', 'fib', 'fibo', 'sys']
dir()不会返回内置的函数和变量。如果要打印内置的话,需要传递__builtin__
>>> import __builtin__
>>> dir(__builtin__)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException',
'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError',
'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FloatingPointError',
'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning',
'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt',
'LookupError', 'MemoryError', 'NameError', 'None', 'NotImplemented',
'NotImplementedError', 'OSError', 'OverflowError',
'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError',
'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError',
'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True',
'TypeError', 'UnboundLocalError', 'UnicodeDecodeError',
'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError',
'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning',
'ZeroDivisionError', '_', '__debug__', '__doc__', '__import__',
'__name__', '__package__', 'abs', 'all', 'any', 'apply', 'basestring',
'bin', 'bool', 'buffer', 'bytearray', 'bytes', 'callable', 'chr',
'classmethod', 'cmp', 'coerce', 'compile', 'complex', 'copyright',
'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval',
'execfile', 'exit', 'file', 'filter', 'float', 'format', 'frozenset',
'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input',
'int', 'intern', 'isinstance', 'issubclass', 'iter', 'len', 'license',
'list', 'locals', 'long', 'map', 'max', 'memoryview', 'min', 'next',
'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit',
'range', 'raw_input', 'reduce', 'reload', 'repr', 'reversed', 'round',
'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super',
'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip']
包
包是组织Python模块的一种方式,比如A.B 标识包A下有一个子模块B。
一个包的结构类似如下:
sound/ Top-level package
__init__.py Initialize the sound package
formats/ Subpackage for file format conversions
__init__.py
wavread.py
wavwrite.py
aiffread.py
aiffwrite.py
auread.py
auwrite.py
...
effects/ Subpackage for sound effects
__init__.py
echo.py
surround.py
reverse.py
...
filters/ Subpackage for filters
__init__.py
equalizer.py
vocoder.py
karaoke.py
...
那么我们怎么导入它:
import sound.effects.echo
然后怎么引用: 必须用全名引用
sound.effects.echo.echofilter(input, output, delay=0.7, atten=4)
另外一种引用的方式是:
from sound.effects import echo
这种方式引入,可以避免全名
echo.echofilter(input, output, delay=0.7, atten=4)
当然,你也可以引入函数或者变量:
from sound.effects.echo import echofilter
直接调用函数:
echofilter(input, output, delay=0.7, atten=4)
注意:以下方式导入,最后一个(subsubitem)必须是包
import item.subitem.subsubitem
导入包
在sound/effects/__init__.py 这个里面定义:
__all__ = ["echo", "surround", "reverse"]
那么:通过以下方式会导入上面all指定的模块
from sound.effects import *
如果all没定义,那么import导入的情况是不一定的。
import sound.effects.echo
import sound.effects.surround
from sound.effects import *
比如上面这种写法,会导入echo和surround
不推荐使用*。
内部包引用
可以使用相对导入:
from . import echo
from .. import formats
from ..filters import equalizer
输入和输出
输出格式
输出方法:sys.stdout标准输出, print write()方法等
格式输出: str.format()
转为字符串用repr()和str()函数 :
>>> s = 'Hello, world.'
>>> str(s)
'Hello, world.'
>>> repr(s)
"'Hello, world.'"
>>> str(1.0/7.0)
'0.142857142857'
>>> repr(1.0/7.0)
'0.14285714285714285'
>>> x = 10 * 3.25
>>> y = 200 * 200
>>> s = 'The value of x is ' + repr(x) + ', and y is ' + repr(y) + '...'
>>> print s
The value of x is 32.5, and y is 40000...
>>> # The repr() of a string adds string quotes and backslashes:
... hello = 'hello, world\n'
>>> hellos = repr(hello)
>>> print hellos
'hello, world\n'
>>> # The argument to repr() may be any Python object:
... repr((x, y, ('spam', 'eggs')))
"(32.5, 40000, ('spam', 'eggs'))"
打印表格形式:
>>> for x in range(1, 11):
... print repr(x).rjust(2), repr(x*x).rjust(3),
... # Note trailing comma on previous line
... print repr(x*x*x).rjust(4)
...
1 1 1
2 4 8
3 9 27
4 16 64
5 25 125
6 36 216
7 49 343
8 64 512
9 81 729
10 100 1000
>>> for x in range(1,11):
... print '{0:2d} {1:3d} {2:4d}'.format(x, x*x, x*x*x)
...
1 1 1
2 4 8
3 9 27
4 16 64
5 25 125
6 36 216
7 49 343
8 64 512
9 81 729
10 100 1000
str.rjust() 对字符串右对齐
str.zfill() 字符串保证位数
>>> '12'.zfill(5)
'00012'
>>> '-3.14'.zfill(7)
'-003.14'
>>> '3.14159265359'.zfill(5)
'3.14159265359'
str.format()的基本使用:
>>> print 'We are the {} who say "{}!"'.format('knights', 'Ni')
We are the knights who say "Ni!"
交换位置:
>>> print '{0} and {1}'.format('spam', 'eggs')
spam and eggs
>>> print '{1} and {0}'.format('spam', 'eggs')
eggs and spam
通过key访问:
>>> print 'This {food} is {adjective}.'.format(
... food='spam', adjective='absolutely horrible')
This spam is absolutely horrible.
混合使用:
>>> print 'The story of {0}, {1}, and {other}.'.format('Bill', 'Manfred',
... other='Georg')
The story of Bill, Manfred, and Georg.
‘!s’ (调用str()) and ‘!r’ (调用repr()) 打印前进行格式转换:
>>> import math
>>> print 'The value of PI is approximately {}.'.format(math.pi)
The value of PI is approximately 3.14159265359.
>>> print 'The value of PI is approximately {!r}.'.format(math.pi)
The value of PI is approximately 3.141592653589793.
‘:’ 可控制小数点:
>>> import math
>>> print 'The value of PI is approximately {0:.3f}.'.format(math.pi)
The value of PI is approximately 3.142.
控制表格:
>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
>>> for name, phone in table.items():
... print '{0:10} ==> {1:10d}'.format(name, phone)
...
Jack ==> 4098
Dcab ==> 7678
Sjoerd ==> 4127
通过[]访问key:
>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
>>> print ('Jack: {0[Jack]:d}; Sjoerd: {0[Sjoerd]:d}; '
... 'Dcab: {0[Dcab]:d}'.format(table))
Jack: 4098; Sjoerd: 4127; Dcab: 8637678
% 操作符也可以格式化(老式的)
>>> import math
>>> print 'The value of PI is approximately %5.3f.' % math.pi
The value of PI is approximately 3.142.
读写文件
open()打开文件:open(filename, mode)
>>> f = open('workfile', 'w')
>>> print f
<open file 'workfile', mode 'w' at 80a0960
‘b’标识二进制形式,跨平台
文件对象的方法
读文件:f.read(size)
>>> f.read()
'This is the entire file.\n'
>>> f.read()
''
带换行:
>>> f.readline()
'This is the first line of the file.\n'
>>> f.readline()
'Second line of the file\n'
>>> f.readline()
''
读取一个文件的所有行:
>> for line in f:
print line,
This is the first line of the file.
Second line of the file
或者list(f) or f.readlines()
字符串写入文件:
>>> f.write('This is a test\n')
将其他类型写入文件需先转为字符串:
>>> value = ('the answer', 42)
>>> s = str(value)
>>> f.write(s)
f.tell() 返回一个整数,表示当前文件的位置(计算字节)。比如:
>>> f = open('workfile', 'r+')
>>> f.write('0123456789abcdef')
>>> f.seek(5) # 到第6个字节
>>> f.read(1)
'5'
>>> f.seek(-3, 2) # 倒数(2表示倒数)第三个字节位置
>>> f.read(1)
'd'
释放文件资源:
>>> f.close()
>>> f.read()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file
最佳实践是带上with:即便有异常抛出也能释放文件资源
>>> with open('workfile', 'r') as f:
... read_data = f.read()
>>> f.closed
True
保存JSON数据
序列化:将json转为字符串 反序列化:将字符串转为json
>>> import json
>>> json.dumps([1, 'simple', 'list'])
'[1, "simple", "list"]'
将对象序列化到一个文件中:f是一个文件对象
json.dump(x, f)
从文件中读取:
x = json.load(f)
错误和异常
语法错误
>>> while True print 'Hello world'
File "<stdin>", line 1
while True print 'Hello world'
^
SyntaxError: invalid syntax
执行异常
>>> 10 * (1/0)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero
>>> 4 + spam*3
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'spam' is not defined
>>> '2' + 2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot concatenate 'str' and 'int' objects
处理异常
>>> while True:
... try:
... x = int(raw_input("Please enter a number: "))
... break
... except ValueError:
... print "Oops! That was no valid number. Try again..."
...
这里只捕获了ValueError,如果捕获更多异常:
... except (RuntimeError, TypeError, NameError):
... pass
import sys
try:
f = open('myfile.txt')
s = f.readline()
i = int(s.strip())
except IOError as e:
print "I/O error({0}): {1}".format(e.errno, e.strerror)
except ValueError:
print "Could not convert data to an integer."
except:
print "Unexpected error:", sys.exc_info()[0]
raise
try…except…else..else后面的代码一定会执行
for arg in sys.argv[1:]:
try:
f = open(arg, 'r')
except IOError:
print 'cannot open', arg
else:
print arg, 'has', len(f.readlines()), 'lines'
f.close()
抛出异常:
>>> try:
... raise Exception('spam', 'eggs')
... except Exception as inst:
... print type(inst) # 异常实例
... print inst.args # arguments 存储在.args中
... print inst # __str__方法使得能直接打印参数而不需要引用它。
... x, y = inst.args
... print 'x =', x
... print 'y =', y
...
<type 'exceptions.Exception'>
('spam', 'eggs')
('spam', 'eggs')
x = spam
函数内部的异常也能捕获:
>>> def this_fails():
... x = 1/0
...
>>> try:
... this_fails()
... except ZeroDivisionError as detail:
... print 'Handling run-time error:', detail
...
Handling run-time error: integer division or modulo by zero
抛出异常
>>> raise NameError('HiThere')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: HiThere
不处理异常,直接将异常抛出:
>>> try:
... raise NameError('HiThere')
... except NameError:
... print 'An exception flew by!'
... raise
...
An exception flew by!
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
NameError: HiThere
自定义异常
>>> class MyError(Exception):
... def __init__(self, value):
... self.value = value
... def __str__(self):
... return repr(self.value)
...
>>> try:
... raise MyError(2*2)
... except MyError as e:
... print 'My exception occurred, value:', e.value
...
My exception occurred, value: 4
>>> raise MyError('oops!')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
__main__.MyError: 'oops!'
重写了__init__方法,并且定义了一个value属性。
一般定义异常的方式是这样的:
class Error(Exception):
"""Base class for exceptions in this module."""
pass
class InputError(Error):
"""Exception raised for errors in the input.
Attributes:
expr -- input expression in which the error occurred
msg -- explanation of the error
"""
def __init__(self, expr, msg):
self.expr = expr
self.msg = msg
class TransitionError(Error):
"""Raised when an operation attempts a state transition that's not
allowed.
Attributes:
prev -- state at beginning of transition
next -- attempted new state
msg -- explanation of why the specific transition is not allowed
"""
def __init__(self, prev, next, msg):
self.prev = prev
self.next = next
self.msg = msg
清理工作
>>> try:
... raise KeyboardInterrupt
... finally:
... print 'Goodbye, world!'
...
Goodbye, world!
KeyboardInterrupt
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
finally总是会被执行,而且如果异常没有被处理的话,在finally里面的代码执行完后会被重新抛出。
一个更复杂点的例子:
>>> def divide(x, y):
... try:
... result = x / y
... except ZeroDivisionError:
... print "division by zero!"
... else:
... print "result is", result
... finally:
... print "executing finally clause"
...
>>> divide(2, 1)
result is 2
executing finally clause
>>> divide(2, 0)
division by zero!
executing finally clause
>>> divide("2", "1")
executing finally clause
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in divide
TypeError: unsupported operand type(s) for /: 'str' and 'str'
预清理
一定要带上with保证文件资源被释放
with open("myfile.txt") as f:
for line in f:
print line,
Python类
定义类
class MyClass:
"""A simple example class"""
i = 12345
def f(self):
return 'hello world'
引用类的属性和方法
MyClass.i和 MyClass.f
MyClass.__doc_ => “A simple example class”
定义init方法,设置默认属性
def __init__(self):
self.data = []
传递给类的参数会传递给init:
>>> class Complex:
... def __init__(self, realpart, imagpart):
... self.r = realpart
... self.i = imagpart
...
>>> x = Complex(3.0, -4.5)
>>> x.r, x.i
(3.0, -4.5)
类共享变量和实例变量
class Dog:
kind = 'canine' # 类共享变量
def __init__(self, name):
self.name = name # 实例变量
>>> d = Dog('Fido')
>>> e = Dog('Buddy')
>>> d.kind # shared by all dogs
'canine'
>>> e.kind # shared by all dogs
'canine'
>>> d.name # unique to d
'Fido'
>>> e.name # unique to e
'Buddy'
注意引用变量避免被所有实例共享
class Dog:
tricks = [] # mistaken use of a class variable
def __init__(self, name):
self.name = name
def add_trick(self, trick):
self.tricks.append(trick)
>>> d = Dog('Fido')
>>> e = Dog('Buddy')
>>> d.add_trick('roll over')
>>> e.add_trick('play dead')
>>> d.tricks # 这里tricks被所有实例共享了
['roll over', 'play dead']
正确的用法:
class Dog:
def __init__(self, name):
self.name = name
self.tricks = [] # creates a new empty list for each dog
def add_trick(self, trick):
self.tricks.append(trick)
>>> d = Dog('Fido')
>>> e = Dog('Buddy')
>>> d.add_trick('roll over')
>>> e.add_trick('play dead')
>>> d.tricks
['roll over']
>>> e.tricks
['play dead']
函数的定义可以在类外部(不推荐)
# Function defined outside the class
def f1(self, x, y):
return min(x, x+y)
class C:
f = f1
def g(self):
return 'hello world'
h = g
通过self引用函数
class Bag:
def __init__(self):
self.data = []
def add(self, x):
self.data.append(x)
def addtwice(self, x):
self.add(x)
self.add(x)
每一个值都是一个对象,它的对象存储在object.__class__
继承
语法:
class DerivedClassName(BaseClassName):
<statement-1>
.
.
.
<statement-N>
或(moduleName是导入的模块)
class DerivedClassName(moduleName.BaseClassName):
如果引用的属性没有在当前类中找到,会找他的基类。继承的类可以重写基类的方法。
有两个内置的函数很有用:
判断实例的类型:isinstance(obj, int) 判断是否是继承自int类 ( 如果
obj.__class__ 是int或者继承自int类 返回true)
issubclass(bool, int): 判断bool是否是int的子类
多继承
class DerivedClassName(Base1, Base2, Base3):
<statement-1>
.
.
.
<statement-N>
私有变量和类内引用
私有变量一般是以_下划线开头
内部调用方法__双下划线开头:
class Mapping:
def __init__(self, iterable):
self.items_list = []
self.__update(iterable)
def update(self, iterable):
for item in iterable:
self.items_list.append(item)
__update = update # 拷贝一份update方法
class MappingSubclass(Mapping):
def update(self, keys, values): # 子类可以重写update方法 并且不会影响到init方法
for item in zip(keys, values):
self.items_list.append(item)
异常也是一个类
语法:
raise Class, instance
raise instance (raise instance.__class__, instance的简写)
比如:
class B:
pass
class C(B):
pass
class D(C):
pass
for c in [B, C, D]:
try:
raise c()
except D:
print "D"
except C:
print "C"
except B:
print "B"
遍历
大部分的对象都可以遍历
for element in [1, 2, 3]:
print element
for element in (1, 2, 3):
print element
for key in {'one':1, 'two':2}:
print key
for char in "123":
print char
for line in open("myfile.txt"):
print line,
内部:for语句调用了iter()方法,然后调用next()方法访问下一个元素,如果没有下一个会抛出StopInteration异常
>>> s = 'abc'
>>> it = iter(s)
>>> it
<iterator object at 0x00A1DB50>
>>> it.next()
'a'
>>> it.next()
'b'
>>> it.next()
'c'
>>> it.next()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
it.next()
StopIteration
给类增加遍历器:
class Reverse:
"""Iterator for looping over a sequence backwards."""
def __init__(self, data):
self.data = data
self.index = len(data)
def __iter__(self):
return self
def next(self):
if self.index == 0:
raise StopIteration
self.index = self.index - 1
return self.data[self.index]
使用:
>>> rev = Reverse('spam')
>>> iter(rev)
<__main__.Reverse object at 0x00A1DB50>
>>> for char in rev:
... print char
...
m
a
p
s
标准库相关
系统接口
>>> import os
>>> os.getcwd() # 返回当前目录
'C:\\Python26'
>>> os.chdir('/server/accesslogs') # 改变工作目录
>>> os.system('mkdir today') # 运行shell命令:mkdir
0
>>> import os
>>> dir(os)
<returns a list of all module functions>
>>> help(os)
<returns an extensive manual page created from the module's docstrings>
文件操作:
>>> import shutil
>>> shutil.copyfile('data.db', 'archive.db')
>>> shutil.move('/build/executables', 'installdir')
文件通配符
>>> import glob
>>> glob.glob('*.py')
['primes.py', 'random.py', 'quote.py']
命令行参数
比如我们跑了这个命令:python demo.py one two three
demo.py里面的写法是:
>>> import sys
>>> print sys.argv
['demo.py', 'one', 'two', 'three']
getopt模块和argparse模块提供了更多灵活的方式访问命令行参数
退出程序和打印错误
sys.exit()
打印错误:
>>> sys.stderr.write('Warning, log file not found starting a new one\n')
Warning, log file not found starting a new one
字符串匹配
>>> import re
>>> re.findall(r'\bf[a-z]*', 'which foot or hand fell fastest')
['foot', 'fell', 'fastest']
>>> re.sub(r'(\b[a-z]+) \1', r'\1', 'cat in the the hat')
'cat in the hat'
>>> 'tea for too'.replace('too', 'two')
'tea for two'
数学
>>> import math
>>> math.cos(math.pi / 4.0)
0.70710678118654757
>>> math.log(1024, 2)
10.0
>>> import random
>>> random.choice(['apple', 'pear', 'banana'])
'apple'
>>> random.sample(xrange(100), 10) # sampling without replacement
[30, 83, 16, 4, 8, 81, 41, 50, 18, 33]
>>> random.random() # random float
0.17970987693706186
>>> random.randrange(6) # random integer chosen from range(6)
4
网络访问
>>> import urllib2
>>> for line in urllib2.urlopen('http://tycho.usno.navy.mil/cgi-bin/timer.pl'):
... if 'EST' in line or 'EDT' in line: # look for Eastern Time
... print line
<BR>Nov. 25, 09:43:32 PM EST
>>> import smtplib
>>> server = smtplib.SMTP('localhost')
>>> server.sendmail('soothsayer@example.org', 'jcaesar@example.org',
... """To: jcaesar@example.org
... From: soothsayer@example.org
...
... Beware the Ides of March.
... """)
>>> server.quit()
日期
>>> # dates are easily constructed and formatted
>>> from datetime import date
>>> now = date.today()
>>> now
datetime.date(2003, 12, 2)
>>> now.strftime("%m-%d-%y. %d %b %Y is a %A on the %d day of %B.")
'12-02-03. 02 Dec 2003 is a Tuesday on the 02 day of December.'
>>> # dates support calendar arithmetic
>>> birthday = date(1964, 7, 31)
>>> age = now - birthday
>>> age.days
14368
数据压缩
>>> import zlib
>>> s = 'witch which has which witches wrist watch'
>>> len(s)
41
>>> t = zlib.compress(s)
>>> len(t)
37
>>> zlib.decompress(t)
'witch which has which witches wrist watch'
>>> zlib.crc32(s)
226805979
性能测试
>>> from timeit import Timer
>>> Timer('t=a; a=b; b=t', 'a=1; b=2').timeit()
0.57535828626024577
>>> Timer('a,b = b,a', 'a=1; b=2').timeit()
0.54962537085770791
质量控制
运行文档内的测试代码:
def average(values):
"""Computes the arithmetic mean of a list of numbers.
>>> print average([20, 30, 70])
40.0
"""
return sum(values, 0.0) / len(values)
import doctest
doctest.testmod() # automatically validate the embedded tests
运行测试集:
import unittest
class TestStatisticalFunctions(unittest.TestCase):
def test_average(self):
self.assertEqual(average([20, 30, 70]), 40.0)
self.assertEqual(round(average([1, 5, 7]), 1), 4.3)
with self.assertRaises(ZeroDivisionError):
average([])
with self.assertRaises(TypeError):
average(20, 30, 70)
unittest.main() # Calling from the command line invokes all tests
格式化输出
>>> import repr
>>> repr.repr(set('supercalifragilisticexpialidocious'))
"set(['a', 'c', 'd', 'e', 'f', 'g', ...])"
自动换行和格式化:
>>> import pprint
>>> t = [[[['black', 'cyan'], 'white', ['green', 'red']], [['magenta',
... 'yellow'], 'blue']]]
...
>>> pprint.pprint(t, width=30)
[[[['black', 'cyan'],
'white',
['green', 'red']],
[['magenta', 'yellow'],
'blue']]]
限制宽度输出:
>>> import textwrap
>>> doc = """The wrap() method is just like fill() except that it returns
... a list of strings instead of one big string with newlines to separate
... the wrapped lines."""
...
>>> print textwrap.fill(doc, width=40)
The wrap() method is just like fill()
except that it returns a list of strings
instead of one big string with newlines
to separate the wrapped lines.
本地化输出:
>>> import locale
>>> locale.setlocale(locale.LC_ALL, 'English_United States.1252')
'English_United States.1252'
>>> conv = locale.localeconv() # get a mapping of conventions
>>> x = 1234567.8
>>> locale.format("%d", x, grouping=True)
'1,234,567'
>>> locale.format_string("%s%.*f", (conv['currency_symbol'],
... conv['frac_digits'], x), grouping=True)
'$1,234,567.80'
模板
>>> from string import Template
>>> t = Template('${village}folk send $$10 to $cause.')
>>> t.substitute(village='Nottingham', cause='the ditch fund')
'Nottinghamfolk send $10 to the ditch fund.'
substitute会替换模板的关键字。如果传递的参数不对会报异常,建议用safe_substitute:
>>> t = Template('Return the $item to $owner.')
>>> d = dict(item='unladen swallow')
>>> t.substitute(d)
Traceback (most recent call last):
...
KeyError: 'owner'
>>> t.safe_substitute(d)
'Return the unladen swallow to $owner.'
自定义分隔符号:
>>> import time, os.path
>>> photofiles = ['img_1074.jpg', 'img_1076.jpg', 'img_1077.jpg']
>>> class BatchRename(Template):
... delimiter = '%'
>>> fmt = raw_input('Enter rename style (%d-date %n-seqnum %f-format): ')
Enter rename style (%d-date %n-seqnum %f-format): Ashley_%n%f
>>> t = BatchRename(fmt)
>>> date = time.strftime('%d%b%y')
>>> for i, filename in enumerate(photofiles):
... base, ext = os.path.splitext(filename)
... newname = t.substitute(d=date, n=i, f=ext)
... print '{0} --> {1}'.format(filename, newname)
img_1074.jpg --> Ashley_0.jpg
img_1076.jpg --> Ashley_1.jpg
img_1077.jpg --> Ashley_2.jpg
多线程
import threading, zipfile
class AsyncZip(threading.Thread):
def __init__(self, infile, outfile):
threading.Thread.__init__(self)
self.infile = infile
self.outfile = outfile
def run(self):
f = zipfile.ZipFile(self.outfile, 'w', zipfile.ZIP_DEFLATED)
f.write(self.infile)
f.close()
print 'Finished background zip of: ', self.infile
background = AsyncZip('mydata.txt', 'myarchive.zip')
background.start()
print 'The main program continues to run in foreground.'
background.join() # Wait for the background task to finish
print 'Main program waited until background was done.'
建议用单线程,然后Queue模块实现多线程的操作,更加容易试错和设计。
日志
import logging
logging.debug('Debugging information')
logging.info('Informational message')
logging.warning('Warning:config file %s not found', 'server.conf')
logging.error('Error occurred')
logging.critical('Critical error -- shutting down')
弱引用
>>> import weakref, gc
>>> class A:
... def __init__(self, value):
... self.value = value
... def __repr__(self):
... return str(self.value)
...
>>> a = A(10) # 创建一个引用
>>> d = weakref.WeakValueDictionary()
>>> d['primary'] = a # 不会创建引用
>>> d['primary'] #
10
>>> del a # 删除
>>> gc.collect() # 运行垃圾回收
0
>>> d['primary'] # 这个时候访问会报错
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
d['primary']
File "C:/python26/lib/weakref.py", line 46, in __getitem__
o = self.data[key]()
KeyError: 'primary'
Lists相关工具集
队列:
>>> from collections import deque
>>> d = deque(["task1", "task2", "task3"])
>>> d.append("task4")
>>> print "Handling", d.popleft()
Handling task1
操作排序:已经排序的插入一个元素
>>> import bisect
>>> scores = [(100, 'perl'), (200, 'tcl'), (400, 'lua'), (500, 'python')]
>>> bisect.insort(scores, (300, 'ruby'))
>>> scores
[(100, 'perl'), (200, 'tcl'), (300, 'ruby'), (400, 'lua'), (500, 'python')]
精确的浮点操作:
>>> from decimal import *
>>> x = Decimal('0.70') * Decimal('1.05')
>>> x
Decimal('0.7350')
>>> x.quantize(Decimal('0.01')) # round to nearest cent
Decimal(huanying guanzhu : '0.74')
>>> round(.70 * 1.05, 2) # same calculation with floats
0.73