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python基础

一 python字符串

在最新的Python 3版本中,字符串是以Unicode编码的,也就是说,Python的字符串支持多语言。

对于单个字符的编码,Python提供了ord()函数获取字符的整数表示,chr()函数把编码转换为对应的字符。

>>> ord(A)65>>> ord()20013>>> chr(66)B>>> chr(25991)>>> \u4e2d\u6587中文

由于Python的字符串类型是str,在内存中以Unicode表示,一个字符对应若干个字节。如果要在网络上传输,或者保存到磁盘上,就需要把str变为以字节为单位的bytes

Python对bytes类型的数据用带b前缀的单引号或双引号表示:

要注意区分‘ABCb‘ABC‘,前者是str,后者虽然内容显示得和前者一样,但bytes的每个字符都只占用一个字节。

以Unicode表示的str通过encode()方法可以编码为指定的bytes,例如:

>>> ABC.encode(ascii)bABC>>> 中文.encode(utf-8)b\xe4\xb8\xad\xe6\x96\x87>>> 中文.encode(ascii)Traceback (most recent call last):  File "<stdin>", line 1, in <module>UnicodeEncodeError: ascii codec cant encode characters in position 0-1: ordinal not in range(128)

纯英文的str可以用ASCII编码为bytes,内容是一样的,含有中文的str可以用UTF-8编码为bytes。含有中文的str无法用ASCII编码,因为中文编码的范围超过了ASCII编码的范围,Python会报错。

bytes中,无法显示为ASCII字符的字节,用\x##显示。

反过来,如果我们从网络或磁盘上读取了字节流,那么读到的数据就是bytes。要把bytes变为str,就需要用decode()方法。

在操作字符串时,我们经常遇到strbytes的互相转换。为了避免乱码问题,应当始终坚持使用UTF-8编码对strbytes进行转换。

由于Python源代码也是一个文本文件,所以,当你的源代码中包含中文的时候,在保存源代码时,就需要务必指定保存为UTF-8编码。当Python解释器读取源代码时,为了让它按UTF-8编码读取,我们通常在文件开头写上这两行:

#!/usr/bin/env python3# -*- coding: utf-8 -*-

申明了UTF-8编码并不意味着你的.py文件就是UTF-8编码的,必须并且要确保文本编辑器正在使用UTF-8 without BOM编码。

 

字符串操作:

技术分享
class str(basestring):    """    str(object=‘‘) -> string        Return a nice string representation of the object.    If the argument is a string, the return value is the same object.    """    def capitalize(self):          """ 首字母变大写 """        """        S.capitalize() -> string                Return a copy of the string S with only its first character        capitalized.        """        return ""    def center(self, width, fillchar=None):          """ 内容居中,width:总长度;fillchar:空白处填充内容,默认无 """        """        S.center(width[, fillchar]) -> string                Return S centered in a string of length width. Padding is        done using the specified fill character (default is a space)        """        return ""    def count(self, sub, start=None, end=None):          """ 子序列个数 """        """        S.count(sub[, start[, end]]) -> int                Return the number of non-overlapping occurrences of substring sub in        string S[start:end].  Optional arguments start and end are interpreted        as in slice notation.        """        return 0    def decode(self, encoding=None, errors=None):          """ 解码 """        """        S.decode([encoding[,errors]]) -> object                Decodes S using the codec registered for encoding. encoding defaults        to the default encoding. errors may be given to set a different error        handling scheme. Default is ‘strict‘ meaning that encoding errors raise        a UnicodeDecodeError. Other possible values are ‘ignore‘ and ‘replace‘        as well as any other name registered with codecs.register_error that is        able to handle UnicodeDecodeErrors.        """        return object()    def encode(self, encoding=None, errors=None):          """ 编码,针对unicode """        """        S.encode([encoding[,errors]]) -> object                Encodes S using the codec registered for encoding. encoding defaults        to the default encoding. errors may be given to set a different error        handling scheme. Default is ‘strict‘ meaning that encoding errors raise        a UnicodeEncodeError. Other possible values are ‘ignore‘, ‘replace‘ and        ‘xmlcharrefreplace‘ as well as any other name registered with        codecs.register_error that is able to handle UnicodeEncodeErrors.        """        return object()    def endswith(self, suffix, start=None, end=None):          """ 是否以 xxx 结束 """        """        S.endswith(suffix[, start[, end]]) -> bool                Return True if S ends with the specified suffix, False otherwise.        With optional start, test S beginning at that position.        With optional end, stop comparing S at that position.        suffix can also be a tuple of strings to try.        """        return False    def expandtabs(self, tabsize=None):          """ 将tab转换成空格,默认一个tab转换成8个空格 """        """        S.expandtabs([tabsize]) -> string                Return a copy of S where all tab characters are expanded using spaces.        If tabsize is not given, a tab size of 8 characters is assumed.        """        return ""    def find(self, sub, start=None, end=None):          """ 寻找子序列位置,如果没找到,返回 -1 """        """        S.find(sub [,start [,end]]) -> int                Return the lowest index in S where substring sub is found,        such that sub is contained within S[start:end].  Optional        arguments start and end are interpreted as in slice notation.                Return -1 on failure.        """        return 0    def format(*args, **kwargs): # known special case of str.format        """ 字符串格式化,动态参数,将函数式编程时细说 """        """        S.format(*args, **kwargs) -> string                Return a formatted version of S, using substitutions from args and kwargs.        The substitutions are identified by braces (‘{‘ and ‘}‘).        """        pass    def index(self, sub, start=None, end=None):          """ 子序列位置,如果没找到,报错 """        S.index(sub [,start [,end]]) -> int                Like S.find() but raise ValueError when the substring is not found.        """        return 0    def isalnum(self):          """ 是否是字母和数字 """        """        S.isalnum() -> bool                Return True if all characters in S are alphanumeric        and there is at least one character in S, False otherwise.        """        return False    def isalpha(self):          """ 是否是字母 """        """        S.isalpha() -> bool                Return True if all characters in S are alphabetic        and there is at least one character in S, False otherwise.        """        return False    def isdigit(self):          """ 是否是数字 """        """        S.isdigit() -> bool                Return True if all characters in S are digits        and there is at least one character in S, False otherwise.        """        return False    def islower(self):          """ 是否小写 """        """        S.islower() -> bool                Return True if all cased characters in S are lowercase and there is        at least one cased character in S, False otherwise.        """        return False    def isspace(self):          """        S.isspace() -> bool                Return True if all characters in S are whitespace        and there is at least one character in S, False otherwise.        """        return False    def istitle(self):          """        S.istitle() -> bool                Return True if S is a titlecased string and there is at least one        character in S, i.e. uppercase characters may only follow uncased        characters and lowercase characters only cased ones. Return False        otherwise.        """        return False    def isupper(self):          """        S.isupper() -> bool                Return True if all cased characters in S are uppercase and there is        at least one cased character in S, False otherwise.        """        return False    def join(self, iterable):          """ 连接 """        """        S.join(iterable) -> string                Return a string which is the concatenation of the strings in the        iterable.  The separator between elements is S.        """        return ""    def ljust(self, width, fillchar=None):          """ 内容左对齐,右侧填充 """        """        S.ljust(width[, fillchar]) -> string                Return S left-justified in a string of length width. Padding is        done using the specified fill character (default is a space).        """        return ""    def lower(self):          """ 变小写 """        """        S.lower() -> string                Return a copy of the string S converted to lowercase.        """        return ""    def lstrip(self, chars=None):          """ 移除左侧空白 """        """        S.lstrip([chars]) -> string or unicode                Return a copy of the string S with leading whitespace removed.        If chars is given and not None, remove characters in chars instead.        If chars is unicode, S will be converted to unicode before stripping        """        return ""    def partition(self, sep):          """ 分割,前,中,后三部分 """        """        S.partition(sep) -> (head, sep, tail)                Search for the separator sep in S, and return the part before it,        the separator itself, and the part after it.  If the separator is not        found, return S and two empty strings.        """        pass    def replace(self, old, new, count=None):          """ 替换 """        """        S.replace(old, new[, count]) -> string                Return a copy of string S with all occurrences of substring        old replaced by new.  If the optional argument count is        given, only the first count occurrences are replaced.        """        return ""    def rfind(self, sub, start=None, end=None):          """        S.rfind(sub [,start [,end]]) -> int                Return the highest index in S where substring sub is found,        such that sub is contained within S[start:end].  Optional        arguments start and end are interpreted as in slice notation.                Return -1 on failure.        """        return 0    def rindex(self, sub, start=None, end=None):          """        S.rindex(sub [,start [,end]]) -> int                Like S.rfind() but raise ValueError when the substring is not found.        """        return 0    def rjust(self, width, fillchar=None):          """        S.rjust(width[, fillchar]) -> string                Return S right-justified in a string of length width. Padding is        done using the specified fill character (default is a space)        """        return ""    def rpartition(self, sep):          """        S.rpartition(sep) -> (head, sep, tail)                Search for the separator sep in S, starting at the end of S, and return        the part before it, the separator itself, and the part after it.  If the        separator is not found, return two empty strings and S.        """        pass    def rsplit(self, sep=None, maxsplit=None):          """        S.rsplit([sep [,maxsplit]]) -> list of strings                Return a list of the words in the string S, using sep as the        delimiter string, starting at the end of the string and working        to the front.  If maxsplit is given, at most maxsplit splits are        done. If sep is not specified or is None, any whitespace string        is a separator.        """        return []    def rstrip(self, chars=None):          """        S.rstrip([chars]) -> string or unicode                Return a copy of the string S with trailing whitespace removed.        If chars is given and not None, remove characters in chars instead.        If chars is unicode, S will be converted to unicode before stripping        """        return ""    def split(self, sep=None, maxsplit=None):          """ 分割, maxsplit最多分割几次 """        """        S.split([sep [,maxsplit]]) -> list of strings                Return a list of the words in the string S, using sep as the        delimiter string.  If maxsplit is given, at most maxsplit        splits are done. If sep is not specified or is None, any        whitespace string is a separator and empty strings are removed        from the result.        """        return []    def splitlines(self, keepends=False):          """ 根据换行分割 """        """        S.splitlines(keepends=False) -> list of strings                Return a list of the lines in S, breaking at line boundaries.        Line breaks are not included in the resulting list unless keepends        is given and true.        """        return []    def startswith(self, prefix, start=None, end=None):          """ 是否起始 """        """        S.startswith(prefix[, start[, end]]) -> bool                Return True if S starts with the specified prefix, False otherwise.        With optional start, test S beginning at that position.        With optional end, stop comparing S at that position.        prefix can also be a tuple of strings to try.        """        return False    def strip(self, chars=None):          """ 移除两段空白 """        """        S.strip([chars]) -> string or unicode                Return a copy of the string S with leading and trailing        whitespace removed.        If chars is given and not None, remove characters in chars instead.        If chars is unicode, S will be converted to unicode before stripping        """        return ""    def swapcase(self):          """ 大写变小写,小写变大写 """        """        S.swapcase() -> string                Return a copy of the string S with uppercase characters        converted to lowercase and vice versa.        """        return ""    def title(self):          """        S.title() -> string                Return a titlecased version of S, i.e. words start with uppercase        characters, all remaining cased characters have lowercase.        """        return ""    def translate(self, table, deletechars=None):          """        转换,需要先做一个对应表,最后一个表示删除字符集合        intab = "aeiou"        outtab = "12345"        trantab = maketrans(intab, outtab)        str = "this is string example....wow!!!"        print str.translate(trantab, xm)        """        """        S.translate(table [,deletechars]) -> string                Return a copy of the string S, where all characters occurring        in the optional argument deletechars are removed, and the        remaining characters have been mapped through the given        translation table, which must be a string of length 256 or None.        If the table argument is None, no translation is applied and        the operation simply removes the characters in deletechars.        """        return ""    def upper(self):          """        S.upper() -> string                Return a copy of the string S converted to uppercase.        """        return ""    def zfill(self, width):          """方法返回指定长度的字符串,原字符串右对齐,前面填充0。"""        """        S.zfill(width) -> string                Pad a numeric string S with zeros on the left, to fill a field        of the specified width.  The string S is never truncated.        """        return ""    def _formatter_field_name_split(self, *args, **kwargs): # real signature unknown        pass    def _formatter_parser(self, *args, **kwargs): # real signature unknown        pass    def __add__(self, y):          """ x.__add__(y) <==> x+y """        pass    def __contains__(self, y):          """ x.__contains__(y) <==> y in x """        pass    def __eq__(self, y):          """ x.__eq__(y) <==> x==y """        pass    def __format__(self, format_spec):          """        S.__format__(format_spec) -> string                Return a formatted version of S as described by format_spec.        """        return ""    def __getattribute__(self, name):          """ x.__getattribute__(name) <==> x.name """        pass    def __getitem__(self, y):          """ x.__getitem__(y) <==> x[y] """        pass    def __getnewargs__(self, *args, **kwargs): # real signature unknown        pass    def __getslice__(self, i, j):          """        x.__getslice__(i, j) <==> x[i:j]                                      Use of negative indices is not supported.        """        pass    def __ge__(self, y):          """ x.__ge__(y) <==> x>=y """        pass    def __gt__(self, y):          """ x.__gt__(y) <==> x>y """        pass    def __hash__(self):          """ x.__hash__() <==> hash(x) """        pass    def __init__(self, string=‘‘): # known special case of str.__init__        """        str(object=‘‘) -> string                Return a nice string representation of the object.        If the argument is a string, the return value is the same object.        # (copied from class doc)        """        pass    def __len__(self):          """ x.__len__() <==> len(x) """        pass    def __le__(self, y):          """ x.__le__(y) <==> x<=y """        pass    def __lt__(self, y):          """ x.__lt__(y) <==> x<y """        pass    def __mod__(self, y):          """ x.__mod__(y) <==> x%y """        pass    def __mul__(self, n):          """ x.__mul__(n) <==> x*n """        pass    @staticmethod # known case of __new__    def __new__(S, *more):          """ T.__new__(S, ...) -> a new object with type S, a subtype of T """        pass    def __ne__(self, y):          """ x.__ne__(y) <==> x!=y """        pass    def __repr__(self):          """ x.__repr__() <==> repr(x) """        pass    def __rmod__(self, y):          """ x.__rmod__(y) <==> y%x """        pass    def __rmul__(self, n):          """ x.__rmul__(n) <==> n*x """        pass    def __sizeof__(self):          """ S.__sizeof__() -> size of S in memory, in bytes """        pass    def __str__(self):          """ x.__str__() <==> str(x) """        passstr
str

二 列表

Python内置的一种数据类型是列表:list。list是一种有序的集合,可以随时添加和删除其中的元素。

技术分享
class list(object):    """    list() -> new empty list    list(iterable) -> new list initialized from iterable‘s items    """    def append(self, p_object): # real signature unknown; restored from __doc__        """ L.append(object) -- append object to end """        pass    def count(self, value): # real signature unknown; restored from __doc__        """ L.count(value) -> integer -- return number of occurrences of value """        return 0    def extend(self, iterable): # real signature unknown; restored from __doc__        """ L.extend(iterable) -- extend list by appending elements from the iterable """        pass    def index(self, value, start=None, stop=None): # real signature unknown; restored from __doc__        """        L.index(value, [start, [stop]]) -> integer -- return first index of value.        Raises ValueError if the value is not present.        """        return 0    def insert(self, index, p_object): # real signature unknown; restored from __doc__        """ L.insert(index, object) -- insert object before index """        pass    def pop(self, index=None): # real signature unknown; restored from __doc__        """        L.pop([index]) -> item -- remove and return item at index (default last).        Raises IndexError if list is empty or index is out of range.        """        pass    def remove(self, value): # real signature unknown; restored from __doc__        """        L.remove(value) -- remove first occurrence of value.        Raises ValueError if the value is not present.        """        pass    def reverse(self): # real signature unknown; restored from __doc__        """ L.reverse() -- reverse *IN PLACE* """        pass    def sort(self, cmp=None, key=None, reverse=False): # real signature unknown; restored from __doc__        """        L.sort(cmp=None, key=None, reverse=False) -- stable sort *IN PLACE*;        cmp(x, y) -> -1, 0, 1        """        pass    def __add__(self, y): # real signature unknown; restored from __doc__        """ x.__add__(y) <==> x+y """        pass    def __contains__(self, y): # real signature unknown; restored from __doc__        """ x.__contains__(y) <==> y in x """        pass    def __delitem__(self, y): # real signature unknown; restored from __doc__        """ x.__delitem__(y) <==> del x[y] """        pass    def __delslice__(self, i, j): # real signature unknown; restored from __doc__        """        x.__delslice__(i, j) <==> del x[i:j]                                      Use of negative indices is not supported.        """        pass    def __eq__(self, y): # real signature unknown; restored from __doc__        """ x.__eq__(y) <==> x==y """        pass    def __getattribute__(self, name): # real signature unknown; restored from __doc__        """ x.__getattribute__(‘name‘) <==> x.name """        pass    def __getitem__(self, y): # real signature unknown; restored from __doc__        """ x.__getitem__(y) <==> x[y] """        pass    def __getslice__(self, i, j): # real signature unknown; restored from __doc__        """        x.__getslice__(i, j) <==> x[i:j]                                      Use of negative indices is not supported.        """        pass    def __ge__(self, y): # real signature unknown; restored from __doc__        """ x.__ge__(y) <==> x>=y """        pass    def __gt__(self, y): # real signature unknown; restored from __doc__        """ x.__gt__(y) <==> x>y """        pass    def __iadd__(self, y): # real signature unknown; restored from __doc__        """ x.__iadd__(y) <==> x+=y """        pass    def __imul__(self, y): # real signature unknown; restored from __doc__        """ x.__imul__(y) <==> x*=y """        pass    def __init__(self, seq=()): # known special case of list.__init__        """        list() -> new empty list        list(iterable) -> new list initialized from iterable‘s items        # (copied from class doc)        """        pass    def __iter__(self): # real signature unknown; restored from __doc__        """ x.__iter__() <==> iter(x) """        pass    def __len__(self): # real signature unknown; restored from __doc__        """ x.__len__() <==> len(x) """        pass    def __le__(self, y): # real signature unknown; restored from __doc__        """ x.__le__(y) <==> x<=y """        pass    def __lt__(self, y): # real signature unknown; restored from __doc__        """ x.__lt__(y) <==> x<y """        pass    def __mul__(self, n): # real signature unknown; restored from __doc__        """ x.__mul__(n) <==> x*n """        pass    @staticmethod # known case of __new__    def __new__(S, *more): # real signature unknown; restored from __doc__        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """        pass    def __ne__(self, y): # real signature unknown; restored from __doc__        """ x.__ne__(y) <==> x!=y """        pass    def __repr__(self): # real signature unknown; restored from __doc__        """ x.__repr__() <==> repr(x) """        pass    def __reversed__(self): # real signature unknown; restored from __doc__        """ L.__reversed__() -- return a reverse iterator over the list """        pass    def __rmul__(self, n): # real signature unknown; restored from __doc__        """ x.__rmul__(n) <==> n*x """        pass    def __setitem__(self, i, y): # real signature unknown; restored from __doc__        """ x.__setitem__(i, y) <==> x[i]=y """        pass    def __setslice__(self, i, j, y): # real signature unknown; restored from __doc__        """        x.__setslice__(i, j, y) <==> x[i:j]=y                                      Use  of negative indices is not supported.        """        pass    def __sizeof__(self): # real signature unknown; restored from __doc__        """ L.__sizeof__() -- size of L in memory, in bytes """        pass    __hash__ = Nonelist
list

三 元组

另一种有序列表叫元组:tuple。tuple和list非常类似,但是tuple一旦初始化就不能修改。不可变的tuple有什么意义?因为tuple不可变,所以代码更安全。如果可能,能用tuple代替list就尽量用tuple。

Python在显示只有1个元素的tuple时,也会加一个逗号,,以免你误解成数学计算意义上的括号。

>>> t = (1,)>>> t(1,)

最后来看一个“可变的”tuple:

>>> t = (a, b, [A, B])>>> t[2][0] = X>>> t[2][1] = Y>>> t(a, b, [X, Y])

这个tuple定义的时候有3个元素,分别是‘a‘‘b‘和一个list。不是说tuple一旦定义后就不可变了吗?怎么后来又变了?

别急,我们先看看定义的时候tuple包含的3个元素:

技术分享

当我们把list的元素‘A‘‘B‘修改为‘X‘‘Y‘后,tuple变为:

技术分享

表面上看,tuple的元素确实变了,但其实变的不是tuple的元素,而是list的元素。tuple一开始指向的list并没有改成别的list,所以,tuple所谓的“不变”是说,tuple的每个元素,指向永远不变。即指向‘a‘,就不能改成指向‘b‘,指向一个list,就不能改成指向其他对象,但指向的这个list本身是可变的!

理解了“指向不变”后,要创建一个内容也不变的tuple怎么做?那就必须保证tuple的每一个元素本身也不能变。

技术分享
class tuple(object):    """    tuple() -> empty tuple    tuple(iterable) -> tuple initialized from iterable‘s items        If the argument is a tuple, the return value is the same object.    """    def count(self, value): # real signature unknown; restored from __doc__        """ T.count(value) -> integer -- return number of occurrences of value """        return 0    def index(self, value, start=None, stop=None): # real signature unknown; restored from __doc__        """        T.index(value, [start, [stop]]) -> integer -- return first index of value.        Raises ValueError if the value is not present.        """        return 0    def __add__(self, y): # real signature unknown; restored from __doc__        """ x.__add__(y) <==> x+y """        pass    def __contains__(self, y): # real signature unknown; restored from __doc__        """ x.__contains__(y) <==> y in x """        pass    def __eq__(self, y): # real signature unknown; restored from __doc__        """ x.__eq__(y) <==> x==y """        pass    def __getattribute__(self, name): # real signature unknown; restored from __doc__        """ x.__getattribute__(‘name‘) <==> x.name """        pass    def __getitem__(self, y): # real signature unknown; restored from __doc__        """ x.__getitem__(y) <==> x[y] """        pass    def __getnewargs__(self, *args, **kwargs): # real signature unknown        pass    def __getslice__(self, i, j): # real signature unknown; restored from __doc__        """        x.__getslice__(i, j) <==> x[i:j]                                      Use of negative indices is not supported.        """        pass    def __ge__(self, y): # real signature unknown; restored from __doc__        """ x.__ge__(y) <==> x>=y """        pass    def __gt__(self, y): # real signature unknown; restored from __doc__        """ x.__gt__(y) <==> x>y """        pass    def __hash__(self): # real signature unknown; restored from __doc__        """ x.__hash__() <==> hash(x) """        pass    def __init__(self, seq=()): # known special case of tuple.__init__        """        tuple() -> empty tuple        tuple(iterable) -> tuple initialized from iterable‘s items                If the argument is a tuple, the return value is the same object.        # (copied from class doc)        """        pass    def __iter__(self): # real signature unknown; restored from __doc__        """ x.__iter__() <==> iter(x) """        pass    def __len__(self): # real signature unknown; restored from __doc__        """ x.__len__() <==> len(x) """        pass    def __le__(self, y): # real signature unknown; restored from __doc__        """ x.__le__(y) <==> x<=y """        pass    def __lt__(self, y): # real signature unknown; restored from __doc__        """ x.__lt__(y) <==> x<y """        pass    def __mul__(self, n): # real signature unknown; restored from __doc__        """ x.__mul__(n) <==> x*n """        pass    @staticmethod # known case of __new__    def __new__(S, *more): # real signature unknown; restored from __doc__        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """        pass    def __ne__(self, y): # real signature unknown; restored from __doc__        """ x.__ne__(y) <==> x!=y """        pass    def __repr__(self): # real signature unknown; restored from __doc__        """ x.__repr__() <==> repr(x) """        pass    def __rmul__(self, n): # real signature unknown; restored from __doc__        """ x.__rmul__(n) <==> n*x """        pass    def __sizeof__(self): # real signature unknown; restored from __doc__        """ T.__sizeof__() -- size of T in memory, in bytes """        passtuple
tuple

四 字典

Python内置了字典:dict的支持,dict全称dictionary,在其他语言中也称为map,使用键-值(key-value)存储,具有极快的查找速度。

把数据放入dict的方法,除了初始化时指定外,还可以通过key放入。

请务必注意,dict内部存放的顺序和key放入的顺序是没有关系的。

和list比较,dict有以下几个特点:

  1. 查找和插入的速度极快,不会随着key的增加而变慢;
  2. 需要占用大量的内存,内存浪费多。

而list相反:

  1. 查找和插入的时间随着元素的增加而增加;
  2. 占用空间小,浪费内存很少。

所以,dict是用空间来换取时间的一种方法。

dict可以用在需要高速查找的很多地方,在Python代码中几乎无处不在,正确使用dict非常重要,需要牢记的第一条就是dict的key必须是不可变对象

这是因为dict根据key来计算value的存储位置,如果每次计算相同的key得出的结果不同,那dict内部就完全混乱了。这个通过key计算位置的算法称为哈希算法(Hash)。

要保证hash的正确性,作为key的对象就不能变。在Python中,字符串、整数等都是不可变的,因此,可以放心地作为key。而list是可变的,就不能作为key。

技术分享
class dict(object):    """    dict() -> new empty dictionary    dict(mapping) -> new dictionary initialized from a mapping object‘s        (key, value) pairs    dict(iterable) -> new dictionary initialized as if via:        d = {}        for k, v in iterable:            d[k] = v    dict(**kwargs) -> new dictionary initialized with the name=value pairs        in the keyword argument list.  For example:  dict(one=1, two=2)    """    def clear(self): # real signature unknown; restored from __doc__        """ 清除内容 """        """ D.clear() -> None.  Remove all items from D. """        pass    def copy(self): # real signature unknown; restored from __doc__        """ 浅拷贝 """        """ D.copy() -> a shallow copy of D """        pass    @staticmethod # known case    def fromkeys(S, v=None): # real signature unknown; restored from __doc__        """        dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v.        v defaults to None.        """        pass    def get(self, k, d=None): # real signature unknown; restored from __doc__        """ 根据key获取值,d是默认值 """        """ D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None. """        pass    def has_key(self, k): # real signature unknown; restored from __doc__        """ 是否有key """        """ D.has_key(k) -> True if D has a key k, else False """        return False    def items(self): # real signature unknown; restored from __doc__        """ 所有项的列表形式 """        """ D.items() -> list of D‘s (key, value) pairs, as 2-tuples """        return []    def iteritems(self): # real signature unknown; restored from __doc__        """ 项可迭代 """        """ D.iteritems() -> an iterator over the (key, value) items of D """        pass    def iterkeys(self): # real signature unknown; restored from __doc__        """ key可迭代 """        """ D.iterkeys() -> an iterator over the keys of D """        pass    def itervalues(self): # real signature unknown; restored from __doc__        """ value可迭代 """        """ D.itervalues() -> an iterator over the values of D """        pass    def keys(self): # real signature unknown; restored from __doc__        """ 所有的key列表 """        """ D.keys() -> list of D‘s keys """        return []    def pop(self, k, d=None): # real signature unknown; restored from __doc__        """ 获取并在字典中移除 """        """        D.pop(k[,d]) -> v, remove specified key and return the corresponding value.        If key is not found, d is returned if given, otherwise KeyError is raised        """        pass    def popitem(self): # real signature unknown; restored from __doc__        """ 获取并在字典中移除 """        """        D.popitem() -> (k, v), remove and return some (key, value) pair as a        2-tuple; but raise KeyError if D is empty.        """        pass    def setdefault(self, k, d=None): # real signature unknown; restored from __doc__        """ 如果key不存在,则创建,如果存在,则返回已存在的值且不修改 """        """ D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D """        pass    def update(self, E=None, **F): # known special case of dict.update        """ 更新            {‘name‘:‘alex‘, ‘age‘: 18000}            [(‘name‘,‘sbsbsb‘),]        """        """        D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.        If E present and has a .keys() method, does:     for k in E: D[k] = E[k]        If E present and lacks .keys() method, does:     for (k, v) in E: D[k] = v        In either case, this is followed by: for k in F: D[k] = F[k]        """        pass    def values(self): # real signature unknown; restored from __doc__        """ 所有的值 """        """ D.values() -> list of D‘s values """        return []    def viewitems(self): # real signature unknown; restored from __doc__        """ 所有项,只是将内容保存至view对象中 """        """ D.viewitems() -> a set-like object providing a view on D‘s items """        pass    def viewkeys(self): # real signature unknown; restored from __doc__        """ D.viewkeys() -> a set-like object providing a view on D‘s keys """        pass    def viewvalues(self): # real signature unknown; restored from __doc__        """ D.viewvalues() -> an object providing a view on D‘s values """        pass    def __cmp__(self, y): # real signature unknown; restored from __doc__        """ x.__cmp__(y) <==> cmp(x,y) """        pass    def __contains__(self, k): # real signature unknown; restored from __doc__        """ D.__contains__(k) -> True if D has a key k, else False """        return False    def __delitem__(self, y): # real signature unknown; restored from __doc__        """ x.__delitem__(y) <==> del x[y] """        pass    def __eq__(self, y): # real signature unknown; restored from __doc__        """ x.__eq__(y) <==> x==y """        pass    def __getattribute__(self, name): # real signature unknown; restored from __doc__        """ x.__getattribute__(‘name‘) <==> x.name """        pass    def __getitem__(self, y): # real signature unknown; restored from __doc__        """ x.__getitem__(y) <==> x[y] """        pass    def __ge__(self, y): # real signature unknown; restored from __doc__        """ x.__ge__(y) <==> x>=y """        pass    def __gt__(self, y): # real signature unknown; restored from __doc__        """ x.__gt__(y) <==> x>y """        pass    def __init__(self, seq=None, **kwargs): # known special case of dict.__init__        """        dict() -> new empty dictionary        dict(mapping) -> new dictionary initialized from a mapping object‘s            (key, value) pairs        dict(iterable) -> new dictionary initialized as if via:            d = {}            for k, v in iterable:                d[k] = v        dict(**kwargs) -> new dictionary initialized with the name=value pairs            in the keyword argument list.  For example:  dict(one=1, two=2)        # (copied from class doc)        """        pass    def __iter__(self): # real signature unknown; restored from __doc__        """ x.__iter__() <==> iter(x) """        pass    def __len__(self): # real signature unknown; restored from __doc__        """ x.__len__() <==> len(x) """        pass    def __le__(self, y): # real signature unknown; restored from __doc__        """ x.__le__(y) <==> x<=y """        pass    def __lt__(self, y): # real signature unknown; restored from __doc__        """ x.__lt__(y) <==> x<y """        pass    @staticmethod # known case of __new__    def __new__(S, *more): # real signature unknown; restored from __doc__        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """        pass    def __ne__(self, y): # real signature unknown; restored from __doc__        """ x.__ne__(y) <==> x!=y """        pass    def __repr__(self): # real signature unknown; restored from __doc__        """ x.__repr__() <==> repr(x) """        pass    def __setitem__(self, i, y): # real signature unknown; restored from __doc__        """ x.__setitem__(i, y) <==> x[i]=y """        pass    def __sizeof__(self): # real signature unknown; restored from __doc__        """ D.__sizeof__() -> size of D in memory, in bytes """        pass    __hash__ = Nonedict
dic

五 集合set

set和dict类似,也是一组key的集合,但不存储value。由于key不能重复,所以,在set中,没有重复的key。

要创建一个set,需要提供一个list作为输入集合:

>>> s = set([1, 2, 3])>>> s{1, 2, 3}

注意,传入的参数[1, 2, 3]是一个list,而显示的{1, 2, 3}只是告诉你这个set内部有1,2,3这3个元素,显示的顺序也不表示set是有序的。。

重复元素在set中自动被过滤:

>>> s = set([1, 1, 2, 2, 3, 3])>>> s{1, 2, 3}
技术分享
class set(object):    """    set() -> new empty set object    set(iterable) -> new set object        Build an unordered collection of unique elements.    """    def add(self, *args, **kwargs): # real signature unknown        """ 添加 """        """        Add an element to a set.                This has no effect if the element is already present.        """        pass    def clear(self, *args, **kwargs): # real signature unknown        """ Remove all elements from this set. """        pass    def copy(self, *args, **kwargs): # real signature unknown        """ Return a shallow copy of a set. """        pass    def difference(self, *args, **kwargs): # real signature unknown        """        Return the difference of two or more sets as a new set.                (i.e. all elements that are in this set but not the others.)        """        pass    def difference_update(self, *args, **kwargs): # real signature unknown        """ 删除当前set中的所有包含在 new set 里的元素 """        """ Remove all elements of another set from this set. """        pass    def discard(self, *args, **kwargs): # real signature unknown        """ 移除元素 """        """        Remove an element from a set if it is a member.                If the element is not a member, do nothing.        """        pass    def intersection(self, *args, **kwargs): # real signature unknown        """ 取交集,新创建一个set """        """        Return the intersection of two or more sets as a new set.                (i.e. elements that are common to all of the sets.)        """        pass    def intersection_update(self, *args, **kwargs): # real signature unknown        """ 取交集,修改原来set """        """ Update a set with the intersection of itself and another. """        pass    def isdisjoint(self, *args, **kwargs): # real signature unknown        """ 如果没有交集,返回true  """        """ Return True if two sets have a null intersection. """        pass    def issubset(self, *args, **kwargs): # real signature unknown        """ 是否是子集 """        """ Report whether another set contains this set. """        pass    def issuperset(self, *args, **kwargs): # real signature unknown        """ 是否是父集 """        """ Report whether this set contains another set. """        pass    def pop(self, *args, **kwargs): # real signature unknown        """ 移除 """        """        Remove and return an arbitrary set element.        Raises KeyError if the set is empty.        """        pass    def remove(self, *args, **kwargs): # real signature unknown        """ 移除 """        """        Remove an element from a set; it must be a member.                If the element is not a member, raise a KeyError.        """        pass    def symmetric_difference(self, *args, **kwargs): # real signature unknown        """ 差集,创建新对象"""        """        Return the symmetric difference of two sets as a new set.                (i.e. all elements that are in exactly one of the sets.)        """        pass    def symmetric_difference_update(self, *args, **kwargs): # real signature unknown        """ 差集,改变原来 """        """ Update a set with the symmetric difference of itself and another. """        pass    def union(self, *args, **kwargs): # real signature unknown        """ 并集 """        """        Return the union of sets as a new set.                (i.e. all elements that are in either set.)        """        pass    def update(self, *args, **kwargs): # real signature unknown        """ 更新 """        """ Update a set with the union of itself and others. """        pass    def __and__(self, y): # real signature unknown; restored from __doc__        """ x.__and__(y) <==> x&y """        pass    def __cmp__(self, y): # real signature unknown; restored from __doc__        """ x.__cmp__(y) <==> cmp(x,y) """        pass    def __contains__(self, y): # real signature unknown; restored from __doc__        """ x.__contains__(y) <==> y in x. """        pass    def __eq__(self, y): # real signature unknown; restored from __doc__        """ x.__eq__(y) <==> x==y """        pass    def __getattribute__(self, name): # real signature unknown; restored from __doc__        """ x.__getattribute__(‘name‘) <==> x.name """        pass    def __ge__(self, y): # real signature unknown; restored from __doc__        """ x.__ge__(y) <==> x>=y """        pass    def __gt__(self, y): # real signature unknown; restored from __doc__        """ x.__gt__(y) <==> x>y """        pass    def __iand__(self, y): # real signature unknown; restored from __doc__        """ x.__iand__(y) <==> x&=y """        pass    def __init__(self, seq=()): # known special case of set.__init__        """        set() -> new empty set object        set(iterable) -> new set object                Build an unordered collection of unique elements.        # (copied from class doc)        """        pass    def __ior__(self, y): # real signature unknown; restored from __doc__        """ x.__ior__(y) <==> x|=y """        pass    def __isub__(self, y): # real signature unknown; restored from __doc__        """ x.__isub__(y) <==> x-=y """        pass    def __iter__(self): # real signature unknown; restored from __doc__        """ x.__iter__() <==> iter(x) """        pass    def __ixor__(self, y): # real signature unknown; restored from __doc__        """ x.__ixor__(y) <==> x^=y """        pass    def __len__(self): # real signature unknown; restored from __doc__        """ x.__len__() <==> len(x) """        pass    def __le__(self, y): # real signature unknown; restored from __doc__        """ x.__le__(y) <==> x<=y """        pass    def __lt__(self, y): # real signature unknown; restored from __doc__        """ x.__lt__(y) <==> x<y """        pass    @staticmethod # known case of __new__    def __new__(S, *more): # real signature unknown; restored from __doc__        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """        pass    def __ne__(self, y): # real signature unknown; restored from __doc__        """ x.__ne__(y) <==> x!=y """        pass    def __or__(self, y): # real signature unknown; restored from __doc__        """ x.__or__(y) <==> x|y """        pass    def __rand__(self, y): # real signature unknown; restored from __doc__        """ x.__rand__(y) <==> y&x """        pass    def __reduce__(self, *args, **kwargs): # real signature unknown        """ Return state information for pickling. """        pass    def __repr__(self): # real signature unknown; restored from __doc__        """ x.__repr__() <==> repr(x) """        pass    def __ror__(self, y): # real signature unknown; restored from __doc__        """ x.__ror__(y) <==> y|x """        pass    def __rsub__(self, y): # real signature unknown; restored from __doc__        """ x.__rsub__(y) <==> y-x """        pass    def __rxor__(self, y): # real signature unknown; restored from __doc__        """ x.__rxor__(y) <==> y^x """        pass    def __sizeof__(self): # real signature unknown; restored from __doc__        """ S.__sizeof__() -> size of S in memory, in bytes """        pass    def __sub__(self, y): # real signature unknown; restored from __doc__        """ x.__sub__(y) <==> x-y """        pass    def __xor__(self, y): # real signature unknown; restored from __doc__        """ x.__xor__(y) <==> x^y """        pass    __hash__ = Noneset
set

 

python基础