# 原创 ： Python Tutorial 2.7.14总结 # Python Tutorial 2.7.14总结 #### 目录 ### 编码风格 [**PEP 8**](https://www.python.org/dev/peps/pep-0008) 引入了大多数项目遵循的风格指导，以下是比较实用的编码风格： ### 数据结构 #### 列表常用函数 对象方法描述 |------ `list.append`(**x**)把一个元素添加到链表的结尾（入栈） `list.pop`([**i**])从链表的指定位置删除元素，**并将其返回**，如果没有指定索引，`a.pop()` 返回最后一个元素。（出栈） `list.sort`(**cmp=None**, **key=None**, **reverse=False**)对链表中的元素就地进行排序 `list.reverse`()就地倒排链表中的元素 `list.remove`(**x**)删除链表中值为 **x** 的第一个元素。如果没有这样的元素，就会返回一个错误。 `list.insert`(**i**, **x**)在指定位置插入一个元素 `list.index`(**x**)返回链表中第一个值为 **x** 的元素的索引，如果没有匹配的元素就会返回一个错误 `list.count`(**x**)返回 **x** 在链表中出现的次数 `list.extend`(**L**)将一个给定列表中的所有元素都添加到另一个列表中，相当于 `a[len(a):] = L` 队列实现`collections.deque()`，`append()`和`popleft()` ``` >>> 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']) ``` #### 函数式编程工具 对于链表： [filter()](https://docs.python.org/2.7/library/functions.html#filter)，[map()](https://docs.python.org/2.7/library/functions.html#map) 以及 [reduce()](https://docs.python.org/2.7/library/functions.html#reduce) ``` >>> 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] ``` ``` >>> def cube(x): return x*x*x ... >>> map(cube, range(1, 11)) [1, 8, 27, 64, 125, 216, 343, 512, 729, 1000] ``` ``` >>> def add(x,y): return x+y ... >>> reduce(add, range(1, 11)) 55 ``` 列表推导式： ``` squares = [x**2 for x in range(10)] ``` #### 元组和序列 元组不可变`>>> singleton = 'hello', # <-- note trailing comma` #### 集合 集合是一个无序不重复元素的集，基本功能包括关系测试和消除重复元素 ``` >>> a = set('abracadabra') >>> a # unique letters in a set(['a', 'r', 'b', 'c', 'd']) >>> a = {x for x in 'abracadabra' if x not in 'abc'} >>> a {'r', 'd'} ``` #### 字典 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} ``` #### 循环技巧 在**序列**中循环时，索引位置和对应值可以使用 [enumerate()](https://docs.python.org/2.7/library/functions.html#enumerate) 函数同时得到: ``` list = ['tic', 'tac', 'toe'] >>> for i, v in enumerate(list): ... print(i, v) ... 0 tic 1 tac 2 toe ``` 多个循环，使用`zip()`整体打包循环： ``` >>> 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. ``` 遍历字典时，使用 `iteritems()` 方法可以同时得到键和对应的值。: ``` >>> knights = {'gallahad': 'the pure', 'robin': 'the brave'} >>> for k, v in knights.iteritems(): ... print k, v ... gallahad the pure robin the brave ``` ### 模块 #### 包 包内引用：包中使用了子包结构，可以按绝对位置从相邻的包中引入子模块 ``` from . import echo from .. import formats from ..filters import equalizer ``` ### 输入与输出 #### 格式化输出 ``` >>> s = 'Hello, world.' >>> str(s) 'Hello, world.' >>> repr(s) "'Hello, world.'" ``` ``` >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678} >>> print 'Jack: {Jack:d}; Sjoerd: {Sjoerd:d}; Dcab: {Dcab:d}'.format(**table) Jack: 4098; Sjoerd: 4127; Dcab: 8637678 ``` ``` >>> import math >>> print 'The value of PI is approximately %5.3f.' % math.pi The value of PI is approximately 3.142. ``` ### 文件读写 #### 使用 [json](https://docs.python.org/2.7/library/json.html#module-json) 存储结构化数据 标准模块 [json](https://docs.python.org/2.7/library/json.html#module-json) 可以接受 Python 数据结构，并将它们转换为字符串表示形式；此过程称为 **序列化**。从字符串表示形式重新构建数据结构称为 **反序列化**。 > JSON 格式经常用于现代应用程序中进行数据交换。许多程序员都已经熟悉它了，使它成为相互协作的一个不错的选择。 ``` >>> json.dumps([1, 'simple', 'list']) '[1, "simple", "list"]' ``` [dumps()](https://docs.python.org/2.7/library/json.html#json.dumps) 函数的另外一个变体 [dump()](https://docs.python.org/2.7/library/json.html#json.dump)，直接将对象序列化到一个文件。所以如果 `f` 是为写入而打开的一个 [文件对象](https://docs.python.org/2.7/glossary.html#term-file-object)，我们可以这样做:`json.dump(x, f)` `x = json.load(f)`：重新解码对象。 ### 错误和异常 ``` try: raise ... except Exception as e: ... finally: ... ``` ### 类 #### 迭代器 大多数容器对象都可以用 [for](https://docs.python.org/2.7/reference/compound_stmts.html#for) 遍历: 在后台，[for](https://docs.python.org/2.7/reference/compound_stmts.html#for) 语句在容器对象中调用 [iter()](https://docs.python.org/2.7/library/functions.html#iter)。 该函数返回一个定义了 [next()](https://docs.python.org/2.7/library/stdtypes.html#iterator.next) 方法的迭代器对象，它在容器中逐一访问元素。没有后续的元素时，[next()](https://docs.python.org/2.7/library/stdtypes.html#iterator.next) 抛出一个 [StopIteration](https://docs.python.org/2.7/library/exceptions.html#exceptions.StopIteration) 异常通知 [for](https://docs.python.org/2.7/reference/compound_stmts.html#for) 语句循环结束。以下是其工作原理的示例: ``` >>> s = 'abc' >>> it = iter(s) >>> it <iterator object at 0x00A1DB50> >>> next(it) 'a' >>> next(it) 'b' >>> next(it) 'c' >>> next(it) Traceback (most recent call last): File "<stdin>", line 1, in ? next(it) StopIteration ``` #### 给自己的类定义迭代器 定义一个 [`__iter__()`](https://docs.python.org/2.7/reference/datamodel.html#object.__iter__) 方法，使其返回一个带有 [next()](https://docs.python.org/2.7/library/stdtypes.html#iterator.next) 方法的对象。如果这个类已经定义了 [next()](https://docs.python.org/2.7/library/stdtypes.html#iterator.next)，那么 [`__iter__()`](https://docs.python.org/2.7/reference/datamodel.html#object.__iter__) 只需要返回 `self`: ``` 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] >>> rev = Reverse('spam') >>> iter(rev) <__main__.Reverse object at 0x00A1DB50> >>> for char in rev: ... print(char) ... m a p s ``` #### 生成器 [yield](https://docs.python.org/2.7/reference/simple_stmts.html#yield) 语句，每次 [next()](https://docs.python.org/2.7/library/functions.html#next) 被调用时，生成器回复它脱离的位置(它记忆语句最后一次执行的位置和所有的数据值)。当发生器终结时，还会自动抛出 [StopIteration](https://docs.python.org/2.7/library/exceptions.html#exceptions.StopIteration)异常。 ``` >>> sum(i*i for i in range(10)) # sum of squares 285 >>> xvec = [10, 20, 30] >>> yvec = [7, 5, 3] >>> sum(x*y for x,y in zip(xvec, yvec)) # dot product 260 >>> from math import pi, sin >>> sine_table = {x: sin(x*pi/180) for x in range(0, 91)} >>> unique_words = set(word for line in page for word in line.split()) >>> valedictorian = max((student.gpa, student.name) for student in graduates) >>> data = 'golf' >>> list(data[i] for i in range(len(data)-1, -1, -1)) ['f', 'l', 'o', 'g'] ``` ### Python标准库概览 #### 操作系统接口 ``` >>> import os >>> os.getcwd() # Return the current working directory 'C:\\Python27' >>> os.chdir('/server/accesslogs') # Change current working directory >>> os.system('mkdir today') # Run the command mkdir in the system shell 0 # 文件管理 >>> import shutil >>> shutil.copyfile('data.db', 'archive.db') >>> shutil.move('/build/executables', 'installdir') # 从目录通配符搜索中生成文件列表 >>> import glob >>> glob.glob('*.py') ['primes.py', 'random.py', 'quote.py'] ``` #### random ``` >>> 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 ``` #### 互联网访问 用于处理从 urls 接收的数据的 [urllib2](https://docs.python.org/2.7/library/urllib2.html#module-urllib2) 以及用于发送电子邮件的 [smtplib](https://docs.python.org/2.7/library/smtplib.html#module-smtplib): ``` >>> import urllib2 >>> for line in urllib2.urlopen('http://tycho.usno.navy.mil/cgi-bin/timer.pl'): ... line = line.decode('utf-8') # Decoding the binary data to text. ... if 'EST' in line or 'EDT' in line: # look for Eastern Time ... print line <BR>Nov. 25, 09:43:32 PM EST # 需要在 localhost 运行一个邮件服务器 >>> 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() ``` #### 日期和时间 ``` >>> # 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 [zlib](https://docs.python.org/2.7/library/zlib.html#module-zlib)，[gzip](https://docs.python.org/2.7/library/gzip.html#module-gzip)，[bz2](https://docs.python.org/2.7/library/bz2.html#module-bz2)，[zipfile](https://docs.python.org/2.7/library/zipfile.html#module-zipfile) 以及 [tarfile](https://docs.python.org/2.7/library/tarfile.html#module-tarfile) ``` >>> import zlib >>> s = b'witch which has which witches wrist watch' >>> len(s) 41 >>> t = zlib.compress(s) >>> len(t) 37 >>> zlib.decompress(t) b'witch which has which witches wrist watch' >>> zlib.crc32(s) 226805979 ``` #### 性能度量 [timeit](https://docs.python.org/2.7/library/timeit.html#module-timeit) ``` >>> 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 ``` > 更多细节见：[http://www.pythondoc.com/pythontutorial27/stdlib2.html](http://www.pythondoc.com/pythontutorial27/stdlib2.html)
参考书籍：[http://www.pythondoc.com/pythontutorial27/](http://www.pythondoc.com/pythontutorial27/)