Guangdong Ocean University Electronic 1151-hole Yanfei Python language programming eighth week

Six, package and module

1 module

     Python中每一个.py脚本定义一个模块，所以我们可以在一个.py脚本中定义一个实现某个功能的函数或者脚本，这样其他的.py脚本就可以调用这个模块了。调用的方式有三种，如下：

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################################### # # Package and Module # # # # # A. py file define a module which can be used in other Script # # As a script, the name of the module is the same as the name of the. py File # # and we use the name to import to a  New Script # # e.g., items.py, import items # # Python contains many. py files, which we can import and use # VI cal.py      def add (x, y): return x + y def sub (x, y): Return xy def mul (x, y): return x * y def div (x, y):   return x/y print "Your answer is:", add (3, 5) if __name__ = = "__main__" R = Add (1, 3) print R # VI test.py Import Cal # would expand cal.py here # So, this would execute the following code in cal.py # print "Your answer is:", Add (3, 5) # It'll print "Your answer Is:8" # But as we import cal.py, we just want to use those functions # so the A Bove code can do this for me, the R=add (1, 3) would not execute result = Cal.add (1, 2) Print result # or import cal as c result = C.add (1, 2) # or from cal Import Add result = Add (1, 2)   

2. Package Packages

   python 的每个.py文件执行某种功能，那有时候我们需要多个.py完成某个更大的功能，或者我们需要将同类功能的.py文件组织到一个地方，这样就可以很方便我们的使用。模块可以按目录组织为包，创建一个包的步骤：

1, create a name for the package name of the folder 2, under the folder created a Init. py empty file 3, store it under this folder as needed. py script file, compiled extension and child package 4, import pack.m1,pack.m2 pack.m3

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#### package 包  ## python 的模块可以按目录组织为包，创建一个包的步骤：  # 1、建立一个名字为包名字的文件夹  # 2、在该文件夹下创建一个__init__.py 空文件  # 3、根据需要在该文件夹下存放.py脚本文件、已编译拓展及子包  # 4、import pack.m1, pack.m2 pack.m3  mkdir calSet  cd calSet  touch __init_.py  cp cal.py .  # vi test.py  import calSet.cal  result = calSet.cal.add(1, 2)  print result  

Vii. Regular Expressions

   正则表达式，（英语：RegularExpression，在代码中常简写为regex、regexp或RE），计算机科学的一个概念。正则表达式使用单个字符串来描述、匹配一系列符合某个句法规则的字符串。在很多文本编辑器里，正则表达式通常被用来检索、替换那些符合某个模式的文本。     Python提供了功能强大的正则表达式引擎re，我们可以利用这个模块来利用正则表达式进行字符串操作。我们用import re来导入这个模块。     正则表达式包含了很多规则，如果能灵活的使用，在匹配字符串方面是非常高效率的。更多的规则，我们需要查阅其他的资料。

1, Meta-character

     很多，一些常用的元字符的使用方法如下：

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############################## # # Regular Expression re # # RE module in python import RE rule = R ' abc ' # r prefix, the rule you wan T to check in a given string re.findall (rule, "AAAAABCAAAAAABCAA") # return [' abc ', ' ABC '] # [] used to specify a character set [ABC] to represent ABC Any one character conforming can rule = r "T[io]p" re.findall (rule, "Tip Tep Twp Top") # return [' Tip ', ' top '] # ^ denotes a complement, e.g. [^io] means other words except I and O  Rule = r "T[^io]p" re.findall (rule, "Tip Tep Twp Top") # return [' Tep ', ' Twp '] # ^ can also match the beginning of the line, indicating to match at the beginning of the line, other places do not match rule =  R "^hello" re.findall (rule, "Hello Tep twp Hello") # return [' Hello '] re.findall (rule, "Tep Twp Hello") # return [] # $  Represents the match line end of rule = R "hello$" re.findall (rule, "Hello Tep twp Hello") # return [' Hello '] re.findall (rule, "Hello Tep Twp") # return [] #-Indicates the range rule = r "X[0123456789]x" # the same as Rule = R "X[0-9]x" re.findall (rule, "x1x x4x xxx") # return [' x1x ', ' x4x '] rule = r "X[a-za-z]x" # \ means escape character rule = r "\^hello" re.findall (rule, "Hello Twp ^hello") # return [' ^hello '] # \d matches a numeric character. Equivalent to [0-9]. # \d matches a non-numeric character.  equivalent to [^0-9]. # \ n matches a line break.  Equivalent to \x0a and \CJ. # \ R matches a carriage return character.  Equivalent to \x0d and \cm. # \s matches any whitespace character, including spaces, tabs, page breaks, and so on.  equivalent to [\f\n\r\t\v]. # \s matches any non-whitespace character.  equivalent to [^ \f\n\r\t\v]. # \ t matches a tab.  Equivalent to \x09 and \ci. # \w matches any word character that includes an underscore.  Equivalent to "[a-za-z0-9_]". # \w matches any non-word character.  Equivalent to "[^a-za-z0-9_]". # {} represents a repeating rule # for example we want to find out if the match is Guangzhou's number, 020-eight bits of data # The following three ways can be implemented Rule = r "^020-\d\d\d\d\d\d\d\d$" rule = r "^020-\d{8}$" # {8} table The preceding rule is repeated 8 times rule = r "^020-[0-9]{8}$" re.findall (rule, "020-23546813") # return [' 020-23546813 '] # * means to repeat the preceding character 0 or more Ru Le = r "ab*" re.findall (Rule, "a") # return [' A '] re.findall (rule, "AB") # return [' AB '] # + means to repeat the preceding character 1 or more rule = r "  ab+ "re.findall (Rule," a ") # return [] re.findall (rule," AB ") # return [' AB '] re.findall (rule," ABB ") # return [' ABB '] # ? Indicates that the preceding character is optional rule = r "^020-?\d{8}$" re.findall (rule, "02023546813") # return [' 020-23546813 re.findall (rule, "020-235468 ") # return [' 020-23546813 '] re.findall (rule," 020--23546813 ") # return [] #?  Represents a non-greedy match rule = r "ab+?" re.fiNdall (rule, "abbbbbbb") # return [' AB '] # {} can represent range rule = r "a{1,3}" re.findall (rule, "a") # return [' A '] Re.findall (r Ule, "AA") # return [' AA '] re.findall (rule, "AAA") # return [' AAA '] re.findall (rule, "AAAA") # return [' AAA ', ' A '] # # C Ompile re String rule = r "\d{3,4}-?\d{8}" re.findall (rule, "020-23546813") # Faster when you compile it # return a obj ECT P_tel = re.compile (rule) p_tel.findall ("020-23546813") # the parameter re. I is case insensitive name_re = Re.compile (r "Xiaoyi", re.   I) Name_re.findall ("Xiaoyi") Name_re.findall ("Xiaoyi") Name_re.findall ("Xiaoyi")

2. Common functions

     Re模块作为一个对象，它还支持很多的操作，例如：

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# the object contain some methods we can use  # match 去搜索字符串开头，如果匹配对，那就返回一个对象，否则返回空  obj = name_re.match(‘Xiaoyi, Zou‘)  # search 去搜索字符串（任何位置），如果匹配对，那就返回一个对象  obj = name_re.search(‘Zou, Xiaoyi‘)  # 然后可以用它来进行判断某字符串是否存在我们的正则表达式  if obj:      pass  # findall 返回一个满足正则的列表  name_re.findall("Xiaoyi")  # finditer 返回一个满足正则的迭代器  name_re.finditer("Xiaoyi")  # 正则替换  rs = r"z..x"  re.sub(rs, ‘python‘, ‘zoux ni ziox me‘) # return ‘python ni python me‘  re.subn(rs, ‘python‘, ‘zoux ni ziox me‘) # return (‘python ni python me‘, 2), contain a number  # 正则切片  str = "123+345-32*78"  re.split(r‘[\+\-\*]‘, str) # return [‘123‘, ‘345‘, ‘32‘, ‘78‘]  # 可以打印re模块支持的属性和方法，然后用help  dir(re)  ##### 编译正则表达式式 可以加入一些属性，可以增加很多功能  # 多行匹配  str = """     hello xiaoyi     xiaoyi hello     hello zou     xiaoyi hello     """  re.findall(r‘xiaoyi‘, str, re.M)  

3. Grouping

     分组有两个作用，它用()来定义一个组，组内的规则只对组内有效。

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# () 分组  email = r"\w{3}@\w+(\.com|\.cn|\.org)"    re.match(email, "[email protected]")  re.match(email, "[email protected]")  re.match(email, "[email protected]")  另外，分组可以优先返回分组内匹配的字符串。

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# 另外，分组可以优先返回分组内匹配的字符串  str = """     idk hello name=zou yes ok d     hello name=xiaoyi yes no dksl     dfi lkasf dfkdf hello name=zouxy yes d     """  r1 = r"hello name=.+ yes"  re.findall(r1, str) # return [‘hello name=zou yes‘, ‘hello name=xiaoyi yes‘, ‘hello name=zouxy yes‘]  r2 = r"hello name=(.+) yes"  re.findall(r2, str) # return [‘zou‘, ‘xiaoyi‘, ‘zouxy‘]  # 可以看到，它会匹配整个正则表达式，但只会返回()括号分组内的字符串，  # 用这个属性，我们就可以进行爬虫，抓取一些想要的数据  

4, a small instance-crawler

     这个实例利用上面的正则和分组的优先返回特性来实现一个小爬虫算法。它的功能是到一个给定的网址里面将.jpg后缀的图片全部下载下来。

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## 一个小爬虫  ## 下载贴吧 或 空间中的所有图片  ## getJpg.py  #!/usr/bin/python  import re  import urllib  # Get the source code of a website  def getHtml(url):      print ‘Getting html source code...‘      page = urllib.open(url)      html = page.read()      return html  # Open the website and check up the address of images,  # and find the common features to decide the re_rule  def getImageAddrList(html):      print ‘Getting all address of images...‘      rule = r"src=\"(.+\.jpg)\" pic_ext"      imReg = re.compile(rule)      imList = re.findall(imReg, html)      return imList  def getImage(imList):      print ‘Downloading...‘      name = 1;      for imgurl in imList:          urllib.urlretrieve(imgurl, ‘%s.jpg‘ % name)          name += 1      print ‘Got ‘, len(imList), ‘ images!‘  ## main  htmlAddr = "http://tieba.baidu.com/p/2510089409"  html = getHtml(htmlAddr)  imList = getImageAddrList(html)  getImage(imList)  

Eight, deep copy and shallow copy

There are two differences in python that need to be noted for copying data:

Shallow copy: A copy of the Reference object (copy only the parent object), deep copy: A copy of the object's resources. The specific differences are as follows:

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##############################  ### memory operation  ## 浅拷贝：对引用对象的拷贝（只拷贝父对象）  ## 深拷贝：对对象资源的拷贝  a = [1, 2, 3]  b = a # id(a) == id (b), 同一个标签，相当于引用  a.append(4) # a = [1, 2, 3, 4], and b also change to = [1, 2, 3, 4]  import copy  a = [1, 2, [‘a‘, ‘b‘]] # 二元列表  c = copy.copy(a)  # id(c) != id(a)  a.append(‘d‘) # a = [1, 2, [‘a‘, ‘b‘], ‘d‘] but c keeps not changed  # 但只属于浅拷贝，只拷贝父对象  # 所以 id(a[0]) == id(c[0])，也就是说对a追加的元素不影响c，  # 但修改a被拷贝的数据后，c的对应数据也会改变，因为拷贝不会改变元素的地址  a[2].append(‘d‘) # will change c, too  a[1] = 3 # will change c, too  # 深拷贝  d = copy.deepcopy(a) # 全部拷贝，至此恩断义绝，两者各走  # 各的阳关道和独木桥，以后毫无瓜葛  

IX. Documents and directories

1. file reading and writing

    Python的文件操作和其他的语言没有太大的差别。通过open或者file类来访问。但python支持了很多的方法，以支持文件内容和list等类型的交互。具体如下：

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########################  ## file and directory  # file_handler = open(filename, mode)  # mode is the same as other program langurage  ## read  # method 1  fin = open(‘./test.txt‘)  fin.read()  fin.close()  # method 2, class file  fin = file(‘./test.txt‘)  fin.read()  fin.close()  ## write  fin = open(‘./test.txt‘, ‘r+‘) # r, r+, w, w+, a, a+, b, U  fin.write(‘hello‘)  fin.close()  ### 文件对象的方法  ## help(file)  for i in open(‘test.txt‘):      print i  str = fin.readline() # 每次读取一行  list = fin.readlines() # 读取多行，返回一个列表，每行作为列表的一个元素  fin.next() # 读取改行，指向下一行  # 用列表来写入多行  fin.writelines(list)  # 移动指针  fin.seek(0, 0)  fin.seek(0, 1)  fin.seek(-1, 2)  # 提交更新  fin.flush() # 平时写数据需要close才真正写入文件，这个函数可以立刻写入文件  

2. OS Module

     os模块提供了很多对系统的操作。例如对目录的操作等。我们需要用import os来插入这个模块以便使用。

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#########################  ## OS module  ## directory operation should import this  import os  os.mkdir(‘xiaoyi‘) # mkdir  os.makedirs(‘a/b/c‘, mode = 666) # 创建分级的目录  os.listdir() # ls 返回当前层所有文件或者文件夹名到一个列表中（不包括子目录）  os.chdir() # cd  os.getcwd() # pwd  os.rmdir() # rm  

3. Directory traversal

   目录遍历的实现可以做很多普遍的功能，例如杀毒软件，垃圾清除软件，文件搜索软件等等。因为他们都涉及到了扫描某目录下所有的包括子目录下的文件。所以需要对目录进行遍历。在这里我们可以使用两种方法对目录进行遍历：

1) recursion

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#!/usr/bin/python  #coding:utf8  import os  def dirList(path):      fileList = os.listdir(path)      allFile = []      for fileName in fileList:          # allFile.append(dirPath + ‘/‘ + fileName) # the same as below          filePath = os.path.join(path, fileName)          if os.path.isdir(filePath):              dirList(filePath)          allFile.append(filePath)      return allFile  

2) Os.walk function

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# os.walk 返回一个生成器，每次是一个三元组 [目录, 子目录, 文件]  gen = os.walk(‘/‘)  for path, dir, filelist in os.walk(‘/‘):      for filename in filelist:          os.path.join(path, filename)  

X. Exception Handling

  异常意味着错误，未经处理的异常会中止程序运行。而异常抛出机制，为程序开发人员提供一种在运行时发现错误，并进行恢复处理，然后继续执行的能力。

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###################################  ### 异常处理  # 异常抛出机制，为程序开发人员提供一种在运行时发现错误，  # 进行恢复处理，然后继续执行的能力  # 用try去尝试执行一些代码，如果错误，就抛出异常，  # 异常由except来捕获，并由我们写代码来处理这种异常  try:      fin = open("abc.txt")      print hello      ### your usually process code here  except IOError, msg:      print "On such file!"      ### your code to handle this error  except NameError, msg:      print msg      ### your code to handle this error  finally: # 不管上面有没有异常，这个代码块都会被执行      print ‘ok‘  # 抛出异常，异常类型要满足python内定义的  if filename == "hello":      raise TypeError("Nothing!!")  

Guangdong Ocean University Electronic 1151-hole Yanfei Python language programming eighth week