424 lines
13 KiB
Markdown
424 lines
13 KiB
Markdown
# 原创
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： Python Tutorial 2.7.14总结
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# Python Tutorial 2.7.14总结
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#### 目录
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### 编码风格
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[**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：
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### 数据结构
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#### 列表常用函数
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<th align="center">对象方法</th><th align="left">描述</th>
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|------
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<td align="center">`list.append`(**x**)</td><td align="left">把一个元素添加到链表的结尾（入栈）</td>
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<td align="center">`list.pop`([**i**])</td><td align="left">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）</td>
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<td align="center">`list.sort`(**cmp=None**, **key=None**, **reverse=False**)</td><td align="left">对链表中的元素就地进行排序</td>
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<td align="center">`list.reverse`()</td><td align="left">就地倒排链表中的元素</td>
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<td align="center">`list.remove`(**x**)</td><td align="left">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。</td>
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<td align="center">`list.insert`(**i**, **x**)</td><td align="left">在指定位置插入一个元素</td>
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<td align="center">`list.index`(**x**)</td><td align="left">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</td>
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<td align="center">`list.count`(**x**)</td><td align="left">返回 **x** 在链表中出现的次数</td>
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<td align="center">`list.extend`(**L**)</td><td align="left">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`</td>
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队列实现`collections.deque()`，`append()`和`popleft()`
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```
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>>> from collections import deque
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>>> queue = deque(["Eric", "John", "Michael"])
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>>> queue.append("Terry") # Terry arrives
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>>> queue.append("Graham") # Graham arrives
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>>> queue.popleft() # The first to arrive now leaves
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'Eric'
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>>> queue.popleft() # The second to arrive now leaves
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'John'
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>>> queue # Remaining queue in order of arrival
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deque(['Michael', 'Terry', 'Graham'])
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```
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#### 函数式编程工具
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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)
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```
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>>> def f(x): return x % 3 == 0 or x % 5 == 0
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...
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>>> filter(f, range(2, 25))
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[3, 5, 6, 9, 10, 12, 15, 18, 20, 21, 24]
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```
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```
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>>> def cube(x): return x*x*x
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...
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>>> map(cube, range(1, 11))
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[1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
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```
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```
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>>> def add(x,y): return x+y
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...
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>>> reduce(add, range(1, 11))
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55
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```
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列表推导式：
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```
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squares = [x**2 for x in range(10)]
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```
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#### 元组和序列
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元组不可变`>>> singleton = 'hello', # <-- note trailing comma`
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#### 集合
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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
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```
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>>> a = set('abracadabra')
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>>> a # unique letters in a
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set(['a', 'r', 'b', 'c', 'd'])
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>>> a = {x for x in 'abracadabra' if x not in 'abc'}
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>>> a
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{'r', 'd'}
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```
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#### 字典
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创建字典：
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```
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>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
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{'sape': 4139, 'jack': 4098, 'guido': 4127}
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>>> {x: x**2 for x in (2, 4, 6)}
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{2: 4, 4: 16, 6: 36}
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```
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#### 循环技巧
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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:
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```
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list = ['tic', 'tac', 'toe']
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>>> for i, v in enumerate(list):
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... print(i, v)
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...
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0 tic
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1 tac
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2 toe
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```
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多个循环，使用`zip()`整体打包循环：
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```
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>>> questions = ['name', 'quest', 'favorite color']
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>>> answers = ['lancelot', 'the holy grail', 'blue']
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>>> for q, a in zip(questions, answers):
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... print 'What is your {0}? It is {1}.'.format(q, a)
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...
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What is your name? It is lancelot.
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What is your quest? It is the holy grail.
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What is your favorite color? It is blue.
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```
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遍历字典时，使用 `iteritems()` 方法可以同时得到键和对应的值。:
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```
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>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
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>>> for k, v in knights.iteritems():
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... print k, v
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...
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gallahad the pure
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robin the brave
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```
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### 模块
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#### 包
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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
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```
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from . import echo
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from .. import formats
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from ..filters import equalizer
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```
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### 输入与输出
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#### 格式化输出
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```
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>>> s = 'Hello, world.'
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>>> str(s)
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'Hello, world.'
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>>> repr(s)
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"'Hello, world.'"
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```
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```
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>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
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>>> print 'Jack: {Jack:d}; Sjoerd: {Sjoerd:d}; Dcab: {Dcab:d}'.format(**table)
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Jack: 4098; Sjoerd: 4127; Dcab: 8637678
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```
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```
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>>> import math
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>>> print 'The value of PI is approximately %5.3f.' % math.pi
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The value of PI is approximately 3.142.
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```
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### 文件读写
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#### 使用 [json](https://docs.python.org/2.7/library/json.html#module-json) 存储结构化数据
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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**。
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>
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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。
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```
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>>> json.dumps([1, 'simple', 'list'])
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'[1, "simple", "list"]'
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```
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[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)`
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`x = json.load(f)`：重新解码对象。
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### 错误和异常
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```
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try:
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raise ...
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except Exception as e:
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...
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finally:
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...
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```
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### 类
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#### 迭代器
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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:
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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:
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```
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>>> s = 'abc'
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>>> it = iter(s)
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>>> it
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<iterator object at 0x00A1DB50>
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>>> next(it)
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'a'
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>>> next(it)
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'b'
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>>> next(it)
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'c'
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>>> next(it)
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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next(it)
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StopIteration
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```
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#### 给自己的类定义迭代器
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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`:
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```
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class Reverse:
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"""Iterator for looping over a sequence backwards."""
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def __init__(self, data):
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self.data = data
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self.index = len(data)
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def __iter__(self):
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return self
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def __next__(self):
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if self.index == 0:
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raise StopIteration
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self.index = self.index - 1
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return self.data[self.index]
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>>> rev = Reverse('spam')
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>>> iter(rev)
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<__main__.Reverse object at 0x00A1DB50>
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>>> for char in rev:
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... print(char)
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...
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m
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a
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p
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s
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```
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#### 生成器
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[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。
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```
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>>> sum(i*i for i in range(10)) # sum of squares
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285
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>>> xvec = [10, 20, 30]
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>>> yvec = [7, 5, 3]
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>>> sum(x*y for x,y in zip(xvec, yvec)) # dot product
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260
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>>> from math import pi, sin
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>>> sine_table = {x: sin(x*pi/180) for x in range(0, 91)}
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>>> unique_words = set(word for line in page for word in line.split())
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>>> valedictorian = max((student.gpa, student.name) for student in graduates)
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>>> data = 'golf'
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>>> list(data[i] for i in range(len(data)-1, -1, -1))
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['f', 'l', 'o', 'g']
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```
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### Python标准库概览
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#### 操作系统接口
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```
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>>> import os
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>>> os.getcwd() # Return the current working directory
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'C:\\Python27'
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>>> os.chdir('/server/accesslogs') # Change current working directory
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>>> os.system('mkdir today') # Run the command mkdir in the system shell
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0
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# 文件管理
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>>> import shutil
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>>> shutil.copyfile('data.db', 'archive.db')
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>>> shutil.move('/build/executables', 'installdir')
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# 从目录通配符搜索中生成文件列表
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>>> import glob
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>>> glob.glob('*.py')
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['primes.py', 'random.py', 'quote.py']
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```
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#### random
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```
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>>> import random
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>>> random.choice(['apple', 'pear', 'banana'])
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'apple'
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>>> random.sample(xrange(100), 10) # sampling without replacement
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[30, 83, 16, 4, 8, 81, 41, 50, 18, 33]
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>>> random.random() # random float
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0.17970987693706186
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>>> random.randrange(6) # random integer chosen from range(6)
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4
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```
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#### 互联网访问
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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):
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```
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>>> import urllib2
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>>> for line in urllib2.urlopen('http://tycho.usno.navy.mil/cgi-bin/timer.pl'):
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... line = line.decode('utf-8') # Decoding the binary data to text.
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... if 'EST' in line or 'EDT' in line: # look for Eastern Time
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... print line
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<BR>Nov. 25, 09:43:32 PM EST
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# 需要在 localhost 运行一个邮件服务器
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>>> import smtplib
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>>> server = smtplib.SMTP('localhost')
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>>> server.sendmail('soothsayer@example.org', 'jcaesar@example.org',
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... """To: jcaesar@example.org
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... From: soothsayer@example.org
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...
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... Beware the Ides of March.
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... """)
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>>> server.quit()
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```
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#### 日期和时间
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```
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>>> # dates are easily constructed and formatted
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>>> from datetime import date
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>>> now = date.today()
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>>> now
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datetime.date(2003, 12, 2)
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>>> now.strftime("%m-%d-%y. %d %b %Y is a %A on the %d day of %B.")
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'12-02-03. 02 Dec 2003 is a Tuesday on the 02 day of December.'
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>>> # dates support calendar arithmetic
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>>> birthday = date(1964, 7, 31)
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>>> age = now - birthday
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>>> age.days
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14368
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```
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#### 数据压缩
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[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)
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```
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>>> import zlib
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>>> s = b'witch which has which witches wrist watch'
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>>> len(s)
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41
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>>> t = zlib.compress(s)
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>>> len(t)
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37
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>>> zlib.decompress(t)
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b'witch which has which witches wrist watch'
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>>> zlib.crc32(s)
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226805979
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```
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#### 性能度量
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[timeit](https://docs.python.org/2.7/library/timeit.html#module-timeit)
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```
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>>> from timeit import Timer
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>>> Timer('t=a; a=b; b=t', 'a=1; b=2').timeit()
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0.57535828626024577
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>>> Timer('a,b = b,a', 'a=1; b=2').timeit()
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0.54962537085770791
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```
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>
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更多细节见：[http://www.pythondoc.com/pythontutorial27/stdlib2.html](http://www.pythondoc.com/pythontutorial27/stdlib2.html)<br/> 参考书籍：[http://www.pythondoc.com/pythontutorial27/](http://www.pythondoc.com/pythontutorial27/)
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