• Python基本数据类型之dict


    一、创建字典:

    d = {
        "name": "morra",        #字典是无序的
        "age": 99,
        "gender": 'm'
    }
    
    a = dict()
    b = dict(k1=123,k2="morra")
    
    
    

    二、基本操作:

    索引

    d = {
        "name": "morra",
        "age": 99,
        "gender": 'm'
    }
    print(d["name"])
    

    键、值、键值对

    keys():获取所有键
    values():获取所有值
    items():获取所有键值对

    d = {
        "name": "morra",
        "age": 99,
        "gender": 'm'
    }
    
    print(d.keys())
    print(type(d.keys()))
    
    print(d.values())
    print(type(d.values()))
    
    print(d.items())
    print(type(d.items()))
    
    OUTPUT:
    dict_keys(['gender', 'age', 'name'])
    <class 'dict_keys'>
    
    dict_values(['m', 99, 'morra'])
    <class 'dict_values'>
    
    dict_items([('gender', 'm'), ('age', 99), ('name', 'morra')])
    <class 'dict_items'>
    

    循环

    for a in d:         #字典在for中默认只能迭代输出key
        print(a)        
    
    OUTPUT:
    name
    gender
    age
    
    #------------------
    
    for i in d.keys():      #迭代输出key
        print(i)
    
    OUTPUT:
    name
    gender
    age
    
    #------------------
    
    for j in d.values():    #迭代输出value
        print(j)
    
    OUTPUT:
    morra
    m
    99
    
    #------------------
    
    for k,v in d.items():   #迭代输出键值对
        print(k,v)
    
    OUTPUT:
    name morra
    gender m
    age 99
    

    取值

    实际上,在使用字典取值的时候使用最多的方法是get()而不是dict[key],因为如果当key值不存在时,使用get()可以调用一个默认值,但是在dict[key]中则会报错。

    d = {
        "name": "morra",
        "age": 99,
        "gender": 'm'
    }
    val1 = d.get('age')
    val2 = d.get('get','123')    #为key设置默认值
    print(val1,val2)
    
    OUTPUT:
    99 123
    

    删除

    pop(k):根据key值移除指定的键值对

    d = {
        "name": "morra",
        "age": 99,
        "gender": 'm'
    }
    
    d.pop("name")
    print(d)
    
    OUTPUT:
    {'gender': 'm', 'age': 99}
    

    popitem():从当前尾部移除键值对,由于字典是无序的,因此被移除的键值对也是随机的。

    d = {
        "name": "morra",
        "age": 99,
        "gender": 'm'
    }
    
    d.popitem()        
    print(d)
    

    del:删除指定索引的键值对,和pop()用法一样

    d = {
        "name": "morra",
        "age": 99,
        "gender": 'm'
    }
    
    del d["name"]
    print(d)
    
    OUTPUT:
    {'age': 99, 'gender': 'm'}
    

    判断

    用in就可以了,但是在python2.7中可以使用has_key()

    批量更新

    update()方法只会更新与原来不同的键值对:

    • 如果key一样,value不一样,则会把原来的value覆盖掉。
    • 如果key不一样则会把两个键值对都添加进来。
    • 如果有一个键值对的key、value和原来一样,则不会更新。
    d = {
        "name": "morra",
        "age": 99,
        "gender": 'm'
    }
    
    d1 = {
        "name": "morra",
        "age1": 991,
        "gender1": 'm1'
    }
    
    d.update(d1)
    for k,v in d.items():
        print(k,v)
    
    OUTPUT:
    name morra
    age1 991
    gender1 m1
    gender m
    age 99
    

    补充

    • fromkeys():
      由于list在迭代的时候没有只有一个值,所以不能直接使用dict(li)把列表转换为字典。在这里我们需要使用字典里的fromkeys()方法。
      fromkeys() :函数用于创建一个新字典,列表中的元素当做key,并为每个key设置一个固定值(value是可选的,如果没有默认为None)。
    seq = ("name","key")
    a = dict.fromkeys(seq)
    b = dict.fromkeys(seq,1)
    
    print(a)
    print(b)
    
    OUTPUT:
    {'key': None, 'name': None}
    {'key': 1, 'name': 1}
    
    • @staticmethod
      一般来说,要使用某个类的方法,需要先实例化一个对象再调用方法,或直接用类调用。而使用staticmethod装饰器之后,就可以不需要实例化,直接类名.方法名()来调用。
      这有利于组织代码,把某些应该属于某个类的函数给放到那个类里去,同时有利于命名空间的整洁。
    @staticmethod 
    def fromkeys(*args, **kwargs):
        """ 
        Returns a new dict with keys from iterable and values equal to value. 
        """
        pass
        
    

    三、源码

    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): 
            """清空字典"""
            """ D.clear() -> None.  Remove all items from D. """
            pass
    
        def copy(self): 
            """ D.copy() -> a shallow copy of D """
            pass
    
        @staticmethod # known case
        def fromkeys(*args, **kwargs): 
            """ Returns a new dict with keys from iterable and values equal to value. """
            pass
    
        def get(self, k, d=None): 
            """ D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None. """
            pass
    
        def items(self): 
            """ D.items() -> a set-like object providing a view on D's items """
            pass
    
        def keys(self): 
            """ D.keys() -> a set-like object providing a view on D's keys """
            pass
    
        def pop(self, k, d=None): 
            """
            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): 
            """
            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): 
            """ 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
            """
            D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
            If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
            If E is present and lacks a .keys() method, then 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): 
            """ D.values() -> an object providing a view on D's values """
            pass
    
        def __contains__(self, *args, **kwargs): 
            """ True if D has a key k, else False. """
            pass
    
        def __delitem__(self, *args, **kwargs): 
            """ Delete self[key]. """
            pass
    
        def __eq__(self, *args, **kwargs): 
            """ Return self==value. """
            pass
    
        def __getattribute__(self, *args, **kwargs): 
            """ Return getattr(self, name). """
            pass
    
        def __getitem__(self, y): 
            """ x.__getitem__(y) <==> x[y] """
            pass
    
        def __ge__(self, *args, **kwargs): 
            """ Return self>=value. """
            pass
    
        def __gt__(self, *args, **kwargs): 
            """ Return self>value. """
            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, *args, **kwargs): 
            """ Implement iter(self). """
            pass
    
        def __len__(self, *args, **kwargs): 
            """ Return len(self). """
            pass
    
        def __le__(self, *args, **kwargs): 
            """ Return self<=value. """
            pass
    
        def __lt__(self, *args, **kwargs): 
            """ Return self<value. """
            pass
    
        @staticmethod # known case of __new__
        def __new__(*args, **kwargs): 
            """ Create and return a new object.  See help(type) for accurate signature. """
            pass
    
        def __ne__(self, *args, **kwargs): 
            """ Return self!=value. """
            pass
    
        def __repr__(self, *args, **kwargs): 
            """ Return repr(self). """
            pass
    
        def __setitem__(self, *args, **kwargs): 
            """ Set self[key] to value. """
            pass
    
        def __sizeof__(self): 
            """ D.__sizeof__() -> size of D in memory, in bytes """
            pass
    
        __hash__ = None
    
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  • 原文地址:https://www.cnblogs.com/whatisfantasy/p/5956761.html
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