Python语法实战指南

1、 Python 语法实战指南目 录 TOC o 1-3 h z u HYPERLINK l _Toc530830033 1.基础语法 PAGEREF _Toc530830033 h 3 HYPERLINK l _Toc530830034 2.表达式与控制流 PAGEREF _Toc530830034 h 9 HYPERLINK l _Toc530830035 3.基本数据类型 PAGEREF _Toc530830035 h 11 HYPERLINK l _Toc530830036 4.集合类型 PAGEREF _Toc530830036 h 17 HYPERLINK l _Toc5308300

2、37 5.函数 PAGEREF _Toc530830037 h 25 HYPERLINK l _Toc530830038 6.类与对象 PAGEREF _Toc530830038 h 31 HYPERLINK l _Toc530830039 7.异常与测试 PAGEREF _Toc530830039 h 37 HYPERLINK l _Toc530830040 8.存储 PAGEREF _Toc530830040 h 39 HYPERLINK l _Toc530830041 9.网络交互 PAGEREF _Toc530830041 h 45 HYPERLINK l _Toc530830042

3、10.数据存储 PAGEREF _Toc530830042 h 47基础语法Python 是一门高阶、动态类型的多范式编程语言；定义 Python 文件的时候我们往往会先声明文件编码方式:# 指定脚本调用方式#!/usr/bin/env python# 配置 utf-8 编码# -*- coding: utf-8 -*-# 配置其他编码# -*- coding: -*-# Vim 中还可以使用如下方式# vim:fileencoding=人生苦短，请用 Python，大量功能强大的语法糖的同时让很多时候 Python 代码看上去有点像伪代码。譬如我们用 Python 实现的简易的快排相较于 J

4、ava 会显得很短小精悍:def quicksort(arr): if len(arr) = 1: return arr pivot = arrlen(arr) / 2 left = x for x in arr if x pivot return quicksort(left) + middle + quicksort(right)print quicksort(3,6,8,10,1,2,1)# Prints 1, 1, 2, 3, 6, 8, 10控制台交互可以根据_name_关键字来判断是否是直接使用 python 命令执行某个脚本，还是外部引用；Google 开源的 fire 也是不错

5、的快速将某个类封装为命令行工具的框架：import fireclass Calculator(object): A simple calculator class. def double(self, number): return 2 * numberif _name_ = _main_: fire.Fire(Calculator)# python calculator.py double 10 # 20# python calculator.py double -number=15 # 30Python 2 中 print 是表达式，而 Python 3 中 print 是函数；如果希望在

6、Python 2 中将 print 以函数方式使用，则需要自定义引入:from _future_ import print_function我们也可以使用 pprint 来美化控制台输出内容：import pprintstuff = spam, eggs, lumberjack, knights, nipprint.pprint(stuff)# 自定义参数pp = pprint.PrettyPrinter(depth=6)tup = (spam, (eggs, (lumberjack, (knights, (ni, (dead,(parrot, (fresh fruit,)pp.pprint(

7、tup)模块Python 中的模块（Module）即是 Python 源码文件，其可以导出类、函数与全局变量；当我们从某个模块导入变量时，函数名往往就是命名空间（Namespace）。而 Python 中的包（Package）则是模块的文件夹，往往由_init_.py指明某个文件夹为包:# 文件目录someDir/ main.py siblingModule.py# siblingModule.pydef siblingModuleFun(): print(Hello from siblingModuleFun)def siblingModuleFunTwo(): print(Hello fr

8、om siblingModuleFunTwo)import siblingModuleimport siblingModule as sibModsibMod.siblingModuleFun()from siblingModule import siblingModuleFunsiblingModuleFun()try: # Import someModuleA that is only available in Windows import someModuleAexcept ImportError: try: # Import someModuleB that is only avail

9、able in Linux import someModuleB except ImportError:Package 可以为某个目录下所有的文件设置统一入口:someDir/ main.py subModules/ _init_.py subA.py subSubModules/ _init_.py subSubA.py# subA.pydef subAFun(): print(Hello from subAFun)def subAFunTwo(): print(Hello from subAFunTwo)# subSubA.pydef subSubAFun(): print(Hello f

10、rom subSubAFun)def subSubAFunTwo(): print(Hello from subSubAFunTwo)# _init_.py from subDir# Adds subAFun() and subAFunTwo() to the subDir namespace from .subA import *# The following two import statement do the same thing, they add subSubAFun() and subSubAFunTwo() to the subDir namespace. The first

11、one assumes _init_.py is empty in subSubDir, and the second one, assumes _init_.py in subSubDir contains from .subSubA import *.# Assumes _init_.py is empty in subSubDir# Adds subSubAFun() and subSubAFunTwo() to the subDir namespacefrom .subSubDir.subSubA import *# Assumes _init_.py in subSubDir has

12、 from .subSubA import *# Adds subSubAFun() and subSubAFunTwo() to the subDir namespacefrom .subSubDir import *# _init_.py from subSubDir# Adds subSubAFun() and subSubAFunTwo() to the subSubDir namespacefrom .subSubA import *# main.pyimport subDirsubDir.subAFun() # Hello from subAFunsubDir.subAFunTwo

13、() # Hello from subAFunTwosubDir.subSubAFun() # Hello from subSubAFunsubDir.subSubAFunTwo() # Hello from subSubAFunTwo表达式与控制流条件选择Python 中使用 if、elif、else 来进行基础的条件选择操作：if x 0: x = 0 print(Negative changed to zero) elif x = 0: print(Zero) else: print(More)Python 同样支持 ternary conditional operator:a if c

14、ondition else b也可以使用 Tuple 来实现类似的效果：# test 需要返回 True 或者 False(falseValue, trueValue)test# 更安全的做法是进行强制判断(falseValue, trueValue)test = True# 或者使用 bool 类型转换函数(falseValue, trueValue)bool()循环遍历for-in 可以用来遍历数组与字典：words = cat, window, defenestratefor w in words: print(w, len(w)# 使用数组访问操作符，能够迅速地生成数组的副本for w

15、 in words: if len(w) 6: words.insert(0, w)# words - defenestrate, cat, window, defenestrate如果我们希望使用数字序列进行遍历，可以使用 Python 内置的range函数：a = Mary, had, a, little, lambfor i in range(len(a): print(i, ai)基本数据类型可以使用内建函数进行强制类型转换（Casting）:int(str)float(str)str(int)str(float)Number: 数值类型x = 3print type(x) # Pri

16、nts print x # Prints 3print x + 1 # Addition; prints 4print x - 1 # Subtraction; prints 2print x * 2 # Multiplication; prints 6print x * 2 # Exponentiation; prints 9x += 1print x # Prints 4x *= 2print x # Prints 8y = 2.5print type(y) # Prints print y, y + 1, y * 2, y * 2 # Prints 2.5 3.5 5.0 6.25布尔类

17、型Python 提供了常见的逻辑操作符，不过需要注意的是 Python 中并没有使用 &、| 等，而是直接使用了英文单词。t = Truef = Falseprint type(t) # Prints print t and f # Logical AND; prints Falseprint t or f # Logical OR; prints Trueprint not t # Logical NOT; prints Falseprint t != f # Logical XOR; prints TrueString: 字符串Python 2 中支持 Ascii 码的 str() 类型，

18、独立的 unicode() 类型，没有 byte 类型；而 Python 3 中默认的字符串为 utf-8 类型，并且包含了 byte 与 bytearray 两个字节类型：type(Guido) # string type is str in python2# # 使用 _future_ 中提供的模块来降级使用 Unicodefrom _future_ import unicode_literalstype(Guido) # string type become unicode# Python 字符串支持分片、模板字符串等常见操作:var1 = Hello World!var2 = Pyth

19、on Programmingprint var10: , var10print var21:5: , var21:5# var10: H# var21:5: ythoprint My name is %s and weight is %d kg! % (Zara, 21)# My name is Zara and weight is 21 kg!str0:4len(str)string.replace(-, ),.join(list)hi 0.format(j)str.find(,)str.index(,) # same, but raises IndexErrorstr.count(,)st

20、r.split(,)str.lower()str.upper()str.title()str.lstrip()str.rstrip()str.strip()str.islower()# 移除所有的特殊字符re.sub(A-Za-z0-9+, , mystring)如果需要判断是否包含某个子字符串，或者搜索某个字符串的下标:# in 操作符可以判断字符串if blah not in somestring: continue# find 可以搜索下标s = This be a stringif s.find(is) = -1: print No is here!else: print Found

21、is in the string.Regex: 正则表达式import re# 判断是否匹配re.match(raeiou, str)# 以第二个参数指定的字符替换原字符串中内容re.sub(raeiou, ?, str)re.sub(r(xyz), r1, str)# 编译生成独立的正则表达式对象expr = pile(r.$)expr.match(.)expr.sub(.)下面列举了常见的表达式使用场景:# 检测是否为 HTML 标签re.search(*, )# 常见的用户名密码re.match(a-zA-Z0-9-_3,16$, Foo) is not Nonere.match(w|-

22、_3,16$, Foo) is not None# Emailre.match(a-z0-9_.-+)(da-z.-+).(a-z.2,6)$, hello.world)# Urlexp = pile(r(https?:/)? # match http or https (da-z.-+) # match domain .(a-z.2,6) # match domain (/w .-*)/?$ # match api or file , re.X)exp.match()# IP 地址exp = pile(r(?:(?:250-5 |20-40-9 |1?0-90-9?).)3 (?:250-5

23、 |20-40-9 |1?0-90-9?)$, re.X)exp.match()集合类型List: 列表Operation: 创建增删list 是基础的序列类型：l = l = list()# 使用字符串的 split 方法，可以将字符串转化为列表str.split(.)# 如果需要将数组拼装为字符串，则可以使用 join list1 = 1, 2, 3str1 = .join(list1)# 如果是数值数组，则需要先进行转换list1 = 1, 2, 3str1 = .join(str(e) for e in list1)可以使用 append 与 extend 向数组中插入元素或者进行数组

24、连接x = 1, 2, 3x.append(4, 5) # 1, 2, 3, 4, 5x.extend(4, 5) # 1, 2, 3, 4, 5，注意 extend 返回值为 None可以使用 pop、slices、del、remove 等移除列表中元素：myList = 10,20,30,40,50# 弹出第二个元素myList.pop(1) # 20# myList: myList.pop(1)# 如果不加任何参数，则默认弹出最后一个元素myList.pop()# 使用 slices 来删除某个元素a = 1, 2, 3, 4, 5, 6 index = 3 # Only Positiv

25、e indexa = a:index + aindex+1 :# 根据下标删除元素myList = 10,20,30,40,50rmovIndxNo = 3del myListrmovIndxNo # myList: 10, 20, 30, 50# 使用 remove 方法，直接根据元素删除letters = a, b, c, d, enumbers.remove(numbers1)print(*letters) # used a * to make it unpack you dont have toIteration: 索引遍历你可以使用基本的 for 循环来遍历数组中的元素，就像下面介个

26、样纸:animals = cat, dog, monkeyfor animal in animals: print animal# Prints cat, dog, monkey, each on its own line.如果你在循环的同时也希望能够获取到当前元素下标，可以使用 enumerate 函数:animals = cat, dog, monkeyfor idx, animal in enumerate(animals): print #%d: %s % (idx + 1, animal)# Prints #1: cat, #2: dog, #3: monkey, each on i

27、ts own linePython 也支持切片（Slices）:nums = range(5) # range is a built-in function that creates a list of integersprint nums # Prints 0, 1, 2, 3, 4print nums2:4 # Get a slice from index 2 to 4 (exclusive); prints 2, 3print nums2: # Get a slice from index 2 to the end; prints 2, 3, 4print nums:2 # Get a

28、slice from the start to index 2 (exclusive); prints 0, 1print nums: # Get a slice of the whole list; prints 0, 1, 2, 3, 4print nums:-1 # Slice indices can be negative; prints 0, 1, 2, 3nums2:4 = 8, 9 # Assign a new sublist to a sliceprint nums # Prints 0, 1, 8, 9, 4Comprehensions: 变换Python 中同样可以使用 m

29、ap、reduce、filter，map 用于变换数组:# 使用 map 对数组中的每个元素计算平方items = 1, 2, 3, 4, 5squared = list(map(lambda x: x*2, items)# map 支持函数以数组方式连接使用def multiply(x): return (x*x)def add(x): return (x+x)funcs = multiply, addfor i in range(5): value = list(map(lambda x: x(i), funcs) print(value)reduce 用于进行归纳计算:# reduce

30、将数组中的值进行归纳from functools import reduceproduct = reduce(lambda x, y: x * y), 1, 2, 3, 4)# Output: 24filter 则可以对数组进行过滤:number_list = range(-5, 5)less_than_zero = list(filter(lambda x: x 0: return positive elif x 0: return negative else: return zerofor x in -1, 0, 1: print sign(x)# Prints negative, zer

31、o, positivePython 支持运行时创建动态函数，也即是所谓的 lambda 函数：def f(x): return x*2# 等价于g = lambda x: x*2参数Option Arguments: 不定参数def example(a, b=None, *args, *kwargs): print a, b print args print kwargsexample(1, var, 2, 3, word=hello)# 1 var# (2, 3)# word: helloa_tuple = (1, 2, 3, 4, 5)a_dict = 1:1, 2:2, 3:3examp

32、le(1, var, *a_tuple, *a_dict)# 1 var# (1, 2, 3, 4, 5)# 1: 1, 2: 2, 3: 3生成器def simple_generator_function(): yield 1 yield 2 yield 3for value in simple_generator_function(): print(value)# 输出结果# 1# 2# 3our_generator = simple_generator_function()next(our_generator)# 1next(our_generator)# 2next(our_gener

33、ator)#3# 生成器典型的使用场景譬如无限数组的迭代def get_primes(number): while True: if is_prime(number): yield number number += 1装饰器装饰器是非常有用的设计模式:# 简单装饰器from functools import wrapsdef decorator(func): wraps(func) def wrapper(*args, *kwargs): print(wrap function) return func(*args, *kwargs) return wrapperdecoratordef ex

34、ample(*a, *kw): passexample._name_ # attr of function preserve# example# Decorator # 带输入值的装饰器from functools import wrapsdef decorator_with_argument(val): def decorator(func): wraps(func) def wrapper(*args, *kwargs): print Val is 0.format(val) return func(*args, *kwargs) return wrapper return decorat

35、ordecorator_with_argument(10)def example(): print This is example function.example()# Val is 10# This is example function.# 等价于def example(): print This is example function.example = decorator_with_argument(10)(example)example()# Val is 10# This is example function.类与对象类定义Python 中对于类的定义也很直接:class Gr

36、eeter(object): # Constructor def _init_(self, name): = name # Create an instance variable # Instance method def greet(self, loud=False): if loud: print HELLO, %s! % .upper() else: print Hello, %s % g = Greeter(Fred) # Construct an instance of the Greeter classg.greet() # Call an instance method; pri

37、nts Hello, Fredg.greet(loud=True) # Call an instance method; prints HELLO, FRED!# isinstance 方法用于判断某个对象是否源自某个类ex = 10isinstance(ex,int)Managed Attributes: 受控属性# property、setter、deleter 可以用于复写点方法class Example(object): def _init_(self, value): self._val = value property def val(self): return self._val

38、 val.setter def val(self, value): if not isintance(value, int): raise TypeError(Expected int) self._val = value val.deleter def val(self): del self._val property def square3(self): return 2*3ex = Example(123)ex.val = str# Traceback (most recent call last):# File , line 1, in# File test.py, line 12,

39、in val# raise TypeError(Expected int)# TypeError: Expected int类方法与静态方法class example(object): classmethod def clsmethod(cls): print I am classmethod staticmethod def stmethod(): print I am staticmethod def instmethod(self): print I am instancemethodex = example()ex.clsmethod()# I am classmethodex.stm

40、ethod()# I am staticmethodex.instmethod()# I am instancemethodexample.clsmethod()# I am classmethodexample.stmethod()# I am staticmethodexample.instmethod()# Traceback (most recent call last):# File , line 1, in# TypeError: unbound method instmethod() .对象实例化属性操作Python 中对象的属性不同于字典键，可以使用点运算符取值，直接使用 in

41、 判断会存在问题:class A(object): property def prop(self): return 3a = A()print prop in a._dict_ =, prop in a._dict_print hasattr(a, prop) =, hasattr(a, prop)print p =, p# prop in a._dict_ = False# hasattr(a, prop) = True# p = 3建议使用 hasattr、getattr、setattr 这种方式对于对象属性进行操作:class Example(object): def _init_(se

42、lf): = ex def printex(self): print This is an example# Check object has attributes# hasattr(obj, attr)ex = Example()hasattr(ex,name)# Truehasattr(ex,printex)# Truehasattr(ex,print)# False# Get object attribute# getattr(obj, attr)getattr(ex,name)# ex# Set object attribute# setattr(obj, attr, value)se

43、tattr(ex,name,example)# example异常与测试异常处理Context Manager - withwith 常用于打开或者关闭某些资源:host = localhostport = 5566with Socket(host, port) as s: while True: conn, addr = s.accept() msg = conn.recv(1024) print msg conn.send(msg) conn.close()单元测试from _future_ import print_functionimport unittestdef fib(n): r

44、eturn 1 if n=2 else fib(n-1)+fib(n-2)def setUpModule(): print(setup module)def tearDownModule(): print(teardown module)class TestFib(unittest.TestCase): def setUp(self): print(setUp) self.n = 10 def tearDown(self): print(tearDown) del self.n classmethod def setUpClass(cls): print(setUpClass) classme

45、thod def tearDownClass(cls): print(tearDownClass) def test_fib_assert_equal(self): self.assertEqual(fib(self.n), 55) def test_fib_assert_true(self): self.assertTrue(fib(self.n) = 55)if _name_ = _main_: unittest.main()存储文件读写路径处理Python 内置的_file_关键字会指向当前文件的相对路径，可以根据它来构造绝对路径，或者索引其他文件:# 获取当前文件的相对目录dir =

46、os.path.dirname(_file_) # srcapp# once youre at the directory level you want, with the desired directory as the final path node:dirname1 = os.path.basename(dir) dirname2 = os.path.split(dir)1 # if you look at the documentation, this is exactly what os.path.basename does.# 获取当前代码文件的绝对路径，abspath 会自动根据

47、相对路径与当前工作空间进行路径补全os.path.abspath(os.path.dirname(_file_) # D:WorkSpaceOWStoolui-tool-svnpythonsrcapp# 获取当前文件的真实路径os.path.dirname(os.path.realpath(_file_) # D:WorkSpaceOWStoolui-tool-svnpythonsrcapp# 获取当前执行路径os.getcwd()可以使用 listdir、walk、glob 模块来进行文件枚举与检索：# 仅列举所有的文件from os import listdirfrom os.path i

48、mport isfile, joinonlyfiles = f for f in listdir(mypath) if isfile(join(mypath, f)# 使用 walk 递归搜索from os import walkf = for (dirpath, dirnames, filenames) in walk(mypath): f.extend(filenames) break# 使用 glob 进行复杂模式匹配import globprint(glob.glob(/home/adam/*.txt)# /home/adam/file1.txt, /home/adam/file2.t

49、xt, 简单文件读写# 可以根据文件是否存在选择写入模式mode = a if os.path.exists(writepath) else w# 使用 with 方法能够自动处理异常with open(file.dat,mode) as f: f.write(.) . # 操作完毕之后记得关闭文件 f.close()# 读取文件内容message = f.read()复杂格式文件JSONimport json# Writing JSON datawith open(data.json, w) as f: json.dump(data, f)# Reading data backwith op

50、en(data.json, r) as f: data = json.load(f)XML我们可以使用lxml来解析与处理 XML 文件，本部分即对其常用操作进行介绍。lxml 支持从字符串或者文件中创建 Element 对象：from lxml import etree# 可以从字符串开始构造xml = root = etree.fromstring(xml)etree.tostring(root)# b# 也可以从某个文件开始构造tree = etree.parse(doc/test.xml)# 或者指定某个 baseURLroot = etree.fromstring(xml, base

51、_url=http:/where.it/is/from.xml)其提供了迭代器以对所有元素进行遍历：# 遍历所有的节点for tag in tree.iter(): if not len(tag): print tag.keys() # 获取所有自定义属性 print (tag.tag, tag.text) # text 即文本子元素值# 获取 XPathfor e in root.iter(): print tree.getpath(e)lxml 支持以 XPath 查找元素，不过需要注意的是，XPath 查找的结果是数组，并且在包含命名空间的情况下，需要指定命名空间：root.xpath(/page/text/text(),ns=prefix:url)# 可以使用 getpare