字典
python中，字典还是一些列的键-值对。每个键都与一个值相关联。键是不可变类型也不能重复，值可以是任意类型，可以将任何python对象用作字典中的值。
键值之间用冒号隔开，键值对之间用逗号隔开。在字典中你存储多少个键值对都可以
sample:
dict_sample = {"name": "甲壳虫~~~", "age": "18"}
创建字典
赋值创建，函数创建
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创建空字典
person1_info = {} -
创建简单单值字典
person2_info = {"name": "甲壳虫"， "age": "18"} -
创建 多个键值对
person2_info = {"name": "甲壳虫"， "age": 18， "sex": "男"， "garde": "七年级"， "addr":["中国"，"江苏省"， "南京市"]， ""friends": {"name1": "Jack", "name2": "Merry"} } -
dict函数
print(dict([()])) """ | 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) 下面还有很多。。。仅仅截取这些 """
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创建空字典
print(dict()) #{} -
创建多个键值对
#（iterable，可迭代对象） cattle = [("name", "甲壳虫~~~"), ("age", 18), ("sex", "男")] print(dict(cattle))#{'name': '甲壳虫~~~', 'age': 18, 'sex': '男'} peach = [["name", "桃子"], ["age", 16], ["sex", "女"]] print(dict(peach))#{'name': '桃子', 'age': 16, 'sex': '女'}
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指定关键字创建字典
1 baby = dict(name="Little Baby", sex="男") 2 print(baby, '~~~', type(baby))#{'name': 'Little Baby', 'sex': '男'} ~~~ <class 'dict'>
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zip()
zip_data = zip(("name", "age", "sex"), ("peach", 16, "girl")) print(dict(zip_data))#{'name': 'peach', 'age': 16, 'sex': 'girl'}
使用字典
字典是键值对形式存在字典中。键和值是一种映射关系。
获取字典中的，值，键和值;
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通过key查询value，如果键不存在怎抛出异常
dic = {"name": "甲壳虫", "age": 18} print(dic['name'])#甲壳虫 print(dic["sex"])#KeyError: 'sex' -
添加键值对
dic = {"name": "甲壳虫", "age": 18} dic['sex'] = '男' print(dic)#{'name': '甲壳虫', 'age': 18, 'sex': '男'} -
删除键值对
dic = {"name": "甲壳虫", "age": 18} dic['sex'] = '男' del dic["age"] print(dic)#{'name': '甲壳虫', 'sex': '男'} -
修改键值对
dic = {"name": "甲壳虫", "age": 18} dic['sex'] = '女' print(dic)#{'name': '甲壳虫', 'age': 18, 'sex': '女'} -
判断字典中是否有对应的键
dic = {"name": "甲壳虫", "age": 18} key_in = "name" in dic print(key_in)#True key_not_in = 'sex' in dic print(key_not_in)#False -
判断字典中是否有对应的值
dic = {"name": "甲壳虫", "age": 18} value_in = "甲壳虫" in dic["name"] print(value_in)其实还是根据键，获取到对应的值，然后在去测试是否在字典中（in ， not in ）
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字典的方法-->字典也是一个类
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clear()方法
dic = {"name": "甲壳虫", "age": 18} """ D.clear() -> None. Remove all items from D. """ a = dic.clear() print(a)#None -
get()方法
dic = {"name": "甲壳虫", "age": 18} """ Return the value for key if key is in the dictionary, else default.None""" print(dic.get("name", "这个默认值是否返回"))#甲壳虫 print(dic.get("sex", "键不在字典中，这里返回了此处设置的默认值"))#键不在字典中，这里返回了此处设置的默认值 -
update（）
dic = {"name": "甲壳虫", "age": 18} """ 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]""" dic.update({"name": "peach"})#键存在 更新键所对应的值 print(dic)#{'name': 'peach', 'age': 18} dic.update({"friend": "peach"})#不键存在 ，添加新的键值对 print(dic)#{'name': 'peach', 'age': 18, 'friend': 'peach'} -
setdefault()
1 dic = {"name": "甲壳虫", "age": 18} 2 """ Insert key with a value of default if key is not in the dictionary. 3 Return the value for key if key is in the dictionary, else default. 4 None""" 5 """如果键不在字典中，向字典中添加对应的键值对；并返回默认值 6 如果键在字典中，直接返回默认的值 7 """ 8 print(dic.setdefault("age", None))#键在字典中，返回键所对应的值 9 print(dic)#{'name': '甲壳虫', 'age': 18} 10 print(dic.setdefault("friend", "键不在字典中"))#键不在字典中,返回设置的值：键不在字典中 11 print(dic)#字典中添加了新的键值对{'name': '甲壳虫', 'age': 18, 'friend': '键不在字典中'}
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pop()
dic = {"name": "甲壳虫", "age": 18} """ D.pop(k[,d]) -> v, remove specified key and return the corresponding value. If key is not found, default is returned if given, otherwise KeyError is raised None""" print(dic.pop("name"))#甲壳虫 print(dic)#{'age': 18} -
popeitem()
dic = {"name": "甲壳虫", "age": 18} """ D.pop(k[,d]) -> v, remove specified key and return the corresponding value. If key is not found, default is returned if given, otherwise KeyError is raised None""" print(dic.popitem())#('age', 18) print(dic)#{'name': '甲壳虫'} -
fromkeys()
"""fromkeys(iterable, value=None, /) method of builtins.type instance Create a new dictionary with keys from iterable and values set to value. None""" lst = ["name-1", "name-2"] dict_tester = dict(dict.fromkeys(lst)) print(dict_tester)#{'name-1': None, 'name-2': None} tup = ("name-1", "name-2") print(dict.fromkeys(tup))#{'name-1': None, 'name-2': None} print(dict.fromkeys(["name-1", "name-2", "姓名"]))#{'name-1': None, 'name-2': None, '姓名': None}
print(dict.fromkeys(["name-1", "name-2"], "姓名"))#{'name-1': '姓名', 'name-2': '姓名'} -
keys(),values(),item()
1 # -*- ecoding: utf-8 -*- 2 # @ModuleName: exercise_demo 3 # @Function: 4 # @Author: 甲壳虫~~~ 5 # @Time: 2021/8/29 8:57 6 #@blog:https://www.cnblogs.com/liveforlearn 7 8 9 cattle = {"name": '甲壳虫~~~', "age": 18, "sex": "男"} 10 11 print('\n', cattle.keys(), type(cattle.keys()))#dict_keys(['name', 'age', 'sex']) <class 'dict_keys'> 12 """ D.keys() -> a set-like object providing a view on D's keys """ 13 for key in cattle.keys(): 14 print(key, end=' ')# name age sex 15 16 print('\n', cattle.values(), type(cattle.values()))#dict_values(['甲壳虫~~~', 18, '男']) <class 'dict_values'> 17 """ D.values() -> an object providing a view on D's values """ 18 for value in cattle.values(): 19 print(value, end=' ')#甲壳虫~~~ 18 男 20 21 print('\n', cattle.items(), type(cattle.items()))#dict_items([('name', '甲壳虫~~~'), ('age', 18), ('sex', '男')]) <class 'dict_items'> 22 """ D.items() -> a set-like object providing a view on D's items """ 23 for k, v in cattle.items(): 24 print(k, v, end=' ')#name 甲壳虫~~~ age 18 sex 男
练一练
统计可迭代对象中的元素
get-->
1 # -*- ecoding: utf-8 -*- 2 # @ModuleName: exercise_demo 3 # @Function: 4 # @Author: 甲壳虫~~~ 5 # @Time: 2021/8/29 8:57 6 #@blog:https://www.cnblogs.com/liveforlearn 7 show = ['刘备', '关羽', '张飞', '曹操', '曹操', '刘备', '曹操', '刘备', '关羽', '曹操'] 8 "简单模拟;统计三国中人名出现的次数" 9 show_times = {} 10 for i in show: 11 show_times[i] = show_times.get(i, 0) + 1 12 print(show_times)#{'刘备': 3, '关羽': 2, '张飞': 1, '曹操': 4}
setdefault-->
# -*- ecoding: utf-8 -*- # @ModuleName: exercise_demo # @Function: # @Author: 甲壳虫~~~ # @Time: 2021/8/29 8:57 #@blog:https://www.cnblogs.com/liveforlearn show = ['刘备', '关羽', '张飞', '曹操', '曹操', '刘备', '曹操', '刘备', '关羽', '曹操'] "简单模拟;统计三国中人名出现的次数" show_times = {} for i in show: show_times.setdefault(i, 0) show_times[i] += 1 print(show_times)#{'刘备': 3, '关羽': 2, '张飞': 1, '曹操': 4}
defaultdict-->
# -*- ecoding: utf-8 -*- # @ModuleName: exercise_demo # @Function: # @Author: 甲壳虫~~~ # @Time: 2021/8/29 8:57 # @blog:https://www.cnblogs.com/liveforlearn show = ['刘备', '关羽', '张飞', '曹操', '曹操', '刘备', '曹操', '刘备', '关羽', '曹操'] "简单模拟;统计三国中人名出现的次数" from collections import defaultdict #用于构建对象，接受一个函数（可调用）对象作为参数。参数返回的类型是什么，key对应的value就是什么类型 """ defaultdict(default_factory[, ...]) --> dict with default factory The default factory is called without arguments to produce a new value when a key is not present, in __getitem__ only. A defaultdict compares equal to a dict with the same items. All remaining arguments are treated the same as if they were passed to the dict constructor, including keyword arguments. """ show_time = defaultdict(list) print(show_time)#defaultdict(<class 'list'>, {}) for (key, value) in show: show_time[key].append(value) print(show_time)#defaultdict(<class 'list'>, {'刘': ['备', '备', '备'], '关': ['羽', '羽'], '张': ['飞'], '曹': ['操', '操', '操', '操']})
试一试
# -*- ecoding: utf-8 -*- # @ModuleName: get_demo # @Function: # @Author: 甲壳虫~~~ # @Time: 2021/8/27 6:36 #@blog:https://www.cnblogs.com/liveforlearn data = [("甲壳虫", 1), ("甲壳虫", 1), ("甲壳虫", 3), ("peach", 1), ("peach", 1), ("peach", 1), ("age", 11), ("age", 12), ("age", 13) ] result = {} # for (key, value) in data: # if key not in result: # result[key] = [] # result[key].append(value) # # print(result) for (key, value) in data: result.setdefault(key, []).append(value) print(result)#{'甲壳虫': [1, 1, 3], 'peach': [1, 1, 1], 'age': [11, 12, 13]} from collections import defaultdict #用于构建对象，接受一个函数（可调用）对象作为参数。参数返回的类型是什么，key对应的value就是什么类型 """ defaultdict(default_factory[, ...]) --> dict with default factory The default factory is called without arguments to produce a new value when a key is not present, in __getitem__ only. A defaultdict compares equal to a dict with the same items. All remaining arguments are treated the same as if they were passed to the dict constructor, including keyword arguments. """ result = defaultdict(list) print(result)#defaultdict(<class 'list'>, {}) for (key, value) in data: result[key].append(value) print(result)#defaultdict(<class 'list'>, {'甲壳虫': [1, 1, 3], 'peach': [1, 1, 1], 'age': [11, 12, 13]}) for (key, value) in data: if key not in result: result[key] = result.get(key, []) result[key].append(value) print(result)#defaultdict(<class 'list'>, {'甲壳虫': [1, 1, 3, 1, 1, 3], 'peach': [1, 1, 1, 1, 1, 1], 'age': [11, 12, 13, 11, 12, 13]})
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