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
