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Python-元组(tuple),文件

时间:2014-08-28 22:30:46      阅读:299      评论:0      收藏:0      [点我收藏+]

标签:os   使用   ar   for   文件   数据   art   代码   sp   

基础:

1. 元组由简单对象组构成。

2. 元组与列表类似,不过不能在原处修改(它们是不可变的),并且通常写成圆括号(),而不是方框号[]中的一系列项。

==========================================================================

>>> (1,2) + (3,4)

(1,2,3,4)

>>> (1,2)*4

(1,2,1,2,1,2,1,2)

>>> T = (1,2,3,4)

>>> T[0], T[1:3]

(1, (2,3))

===========================================================================

>>> x = (40)  # An integer!

>>> x

40

>>> y = (40,)  #A tuple containing an integer

>>> y

(40,)

注:在不会引发语法冲突的情况系啊,Python允许忽略元组的圆括号。

如果圆括号里的单一对象是元组对象而不是一个简单的表达式(圆括号可以把表达式括起来), 需要对Python进行特别说明。

如果确实像得到一个远足,只要在这一单个元素之后,关闭圆括号之前加一个逗号即可。

=============================================================================

>>> T = (‘cc‘, ‘aa‘, ‘dd‘, ‘bb’)

>>> tmp = list(T)          # Make a list from a tuple‘s items

>>> tmp.sort()

>>> tmp

[‘aa‘, ‘bb‘, ‘cc‘, ‘dd‘]

>>> T = tuple(tmp)          # Make a tumple from the list‘s items

>>> T

(‘aa‘, ‘bb‘, ‘cc‘, ‘dd‘)

>>> sorted(T)            # Or use the sorted built-in

[‘aa‘, ‘bb‘, ‘cc‘, ‘dd‘]

=============================================================================

>>> T = (1, [2,3], 4)

>>> T[1] = ‘spam‘        # This fails: can‘t change tuple itself

TypeError

>>> T[1][0] = ‘spam‘       # This works: can change mutables inside

>>> T

(1, [‘spam‘, 3], 4)

=============================================================================

eval能够把字符串当做可执行程序代码(从技术上来讲,就是一个含有Python表达式的字符串)

>>> line = "[1,2,3]${‘a‘:1, ‘b‘:2}\n"

>>> line

"[1,2,3]${‘a‘:1, ‘b‘:2}\n"

>>> parts = line.split(‘$‘)

>>> parts

[‘[1,2,3]‘,"{‘a‘:1, ‘b‘:2}\n"]

>>> eval(parts[0])

[1,2,3]

>>> objects = [eval(P) for P in parts]

>>> objects

[[1,2,3], {‘a‘:1, ‘b‘:2}]

=========================================================

用pickle存储Python的原生对象

pickle与eval的区别:

eval能够执行Python的任何表达式,有可能会删除计算机上所有文件的表达式;

pickle能够存储Python原生对象,也不要求把字符串转换。

>>> D = {‘a‘: 1, ‘b‘: 2}

>>> F = open(‘datafile.pkl‘, ‘wb‘)

>>> import pickle

>>> pickle.dump(D, F)      # Pickle any object to file

>>> F.close()

之后想要取回字典时,只要简单的再用一次pickle进行重建就可以了;

>>> F = open(‘datafile.pkl‘, ‘wb‘)

>>> E = pickle.load(F)

>>> E

{‘a‘: 1, ‘b‘: 2}

>>> open(‘datafile.pkl‘, ‘rb‘).read()        # Format is prone to change!

b‘\x90\x03}q\x00(X\x01\x00\x00…….‘

注:在这里是使用二进制模式打开用于储存pickle化的对象的文件,因为二进制模式总是Python 3.X中必须的,同时pickle程序创建和使用一个bytes字符串对象,并且这些对象意味着二进制模式文件(文本模式文件意味着Python 3.X中的str字符串)

===========================================================

struct模块能够创造并解析打包的二进制数据;

从某种意义上说,它是另一个数据转换工具。

>>> F = open(‘data.bin‘, ‘wb‘)

>>> import struct

>>> data = struct.pack(‘>i4sh‘, 7, ‘spam‘, 8)      # Make packed binary data

>>> data

b‘\x00\x00\x00\x07spam\x00\x08‘

>>> F.wirte(data)                    # Write byte string

>>> F.close()

 

>>> F = open(‘data.bin‘, ‘rb‘)

>>> data = F.read()

>>> data

b‘\x00\x00\x00\x07spam\x00\x08‘

>>> values = struct.unpack(‘>i4sh‘, data)        # Convert to Python objects

>>> values

(7, ‘spam‘, 8)

=========================================================

引用:

>>> X = [1,2,3]

>>> L = [‘a‘, X, ‘b‘]

>>> D = {‘x‘: X, ‘y‘: 2}

>>> X[1] = ‘surprise‘

>>> L 

[‘a‘, [1, ‘surprise‘, 3], ‘b‘]

>>> D

{‘x‘: [1, ‘surprise‘, 3], ‘y‘: 2}

 

复制:

>>> L = [1,2,3]

>>> D = {‘a‘: 1, ‘b‘: 2}

>>> A = L[:]

>>> B = D.copy()

>>> A[1] = ‘N1‘

>>> D[‘c‘] = ‘spam‘

>>> L,D

([1,2,3], {‘a‘: 1, ‘c‘: ‘spam‘, ‘b‘: 2})

>>> A,B

([1, ‘Ni‘, 3], {‘a‘: 1, ‘b‘: 2})

如果将引用中修改为

>>> X = [1,2,3]

>>> L = [‘a‘: X[:], ‘b‘]

>>> D = {‘x‘: X[:], ‘y‘: 2]

则X的修改不会影响到L与D

========================================================

判断“一致性”与“相等性”

>>> L1 = [1,(‘a‘, 3)]

>>> L2 = [1,(‘a‘, 3)]

>>> L1 == L2, L1 is L2

(True, False)

“==”判断相等性,“is”判断一致性;

>>> S1 = ‘spam‘

>>> S2 = ‘spam‘

>>> S1 == S2, S1 is S2

(True, True)

>>> S1 = ‘a longer string‘

>>> S2 = ‘a longer string‘

>>> S1 == S2, S1 is S2

(True, false)

理由:

Python内部暂时存储并重复使用段字符串作为最佳化,因为‘spam‘实际上在内存中只存在一个字符串用于分享;

 

Python-元组(tuple),文件

标签:os   使用   ar   for   文件   数据   art   代码   sp   

原文地址:http://www.cnblogs.com/yy-is-ing/p/3942747.html

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