____tz_zs
一、字典（dict）
字典类型（dict）是“键–值”数据项的组合，每个元素是一个键值对。如：身份证号（键）–个人信息（值）。值可以取任何数据类型，但键必须是不可变的，如字符串，数字或元组。
字典类型的数据是无序的，字典类型数据通过映射查找数据项。
（一）创建 dict
使用 dict() 函数dict1 = {'a': 1, 'b': 2}print(dict1) # {'a': 1, 'b': 2}dict2 = dict(a=1, b=2)print(dict2) # {'a': 1, 'b': 2}dict3 = dict([('a', 1), ('b', 2)])print(dict3) # {'a': 1, 'b': 2}
使用 dict.fromkeys()
dict.fromkeys(可迭代对象，默认值)
asset_list = ['aa', 'bb', 'cc']d = dict.fromkeys(asset_list, 0.) #print(d) # {'aa': 0.0, 'bb': 0.0, 'cc': 0.0}
字典生成式
# 两个列表 list 组合成字典 dictd1 = {k: v for k in ['a', 'b', 'c'] for v in ['A', 'B', 'C']} # 两两组合，错误方法，因为每个键对应一个值，在循环中，值'C' 将 值"B'和'A' 替换了print(d1) # {'a': 'C', 'c': 'C', 'b': 'C'}d2 = {k: v for k, v in [('a', 'A'), ('b', 'B'), ('c', 'C')]}print(d2) # {'a': 'A', 'b': 'B', 'c': 'C'}d3 = {k: v for k, v in zip(['a', 'b', 'c'], ['A', 'B', 'C'])}print(d3) # {'a': 'A', 'b': 'B', 'c': 'C'}# 关于zip() 函数z = zip(['a', 'b', 'c'], ['A', 'B', 'C']) # zip() 函数用于将可迭代的对象作为参数，将对象中对应的元素打包成一个个元组，然后返回由这些元组组成的对象。print(type(z)) # <class 'zip'>print(z) # <zip object at 0x000001C8505EE288>l = list(z) # list() 转换为列表print(l) # [('a', 'A'), ('b', 'B'), ('c', 'C')]# 多层循环创建 dictprint({k: {v: 1} for k in ['a', 'b', 'c'] for v in ['A', 'B', 'C']}) # 多级字典，错误方法# {'b': {'C': 1}, 'c': {'C': 1}, 'a': {'C': 1}}print({k: {v: 1 for v in ['A', 'B', 'C']} for k in ['a', 'b', 'c']}) # 多级字典# {'b': {'B': 1, 'C': 1, 'A': 1}, 'c': {'B': 1, 'C': 1, 'A': 1}, 'a': {'B': 1, 'C': 1, 'A': 1}}
字典生成式的一些使用
tag_list = [{"price": "1.1", "value": "100", "signal": True},{"price": "1.2", "value": "200", "signal": True},{"price": "1.3", "value": "300", "signal": False}]# 筛选字典format_tag1 = [{k: v for k, v in d.items()} for d in tag_list if d["signal"] is True]print(format_tag1) # [{'price': '1.1', 'value': '100', 'signal': True}, {'price': '1.2', 'value': '200', 'signal': True}]# 修改字典中的数据format_tag2 = [{k: float(v) for k, v in d.items()} for d in tag_list]print(format_tag2) # [{'price': 1.1, 'value': 100.0, 'signal': 1.0}, {'price': 1.2, 'value': 200.0, 'signal': 1.0}, {'price': 1.3, 'value': 300.0, 'signal': 0.0}]format_tag3 = [{k: float(v) if not isinstance(v, bool) else v for k, v in d.items()} for d in tag_list]print(format_tag3) # [{'price': 1.1, 'value': 100.0, 'signal': True}, {'price': 1.2, 'value': 200.0, 'signal': True}, {'price': 1.3, 'value': 300.0, 'signal': False}]format_tag4 = [{k if k != "signal" else k.upper(): float(v) if not isinstance(v, bool) else v for k, v in d.items()} for d in tag_list]print(format_tag4) # [{'price': 1.1, 'value': 100.0, 'SIGNAL': True}, {'price': 1.2, 'value': 200.0, 'SIGNAL': True}, {'price': 1.3, 'value': 300.0, 'SIGNAL': False}]
使用 df 创建字典
#!/usr/bin/python2.7# -*- coding:utf-8 -*-"""@author: tz_zs"""import numpy as npimport pandas as pdimport matplotlib.pyplot as pltlist_l = [[1, 3, 3, 5, 4.], [11, 7, 15, 13, 9.1], [4, 2, 7, 9, 3.5], [15, 11, 12, 6, 11.1]]index = ["-07-01", "-07-02", "-07-03", "-07-04"]col = ['a', 'b', 'c', 'd', 'e']df = pd.DataFrame(list_l, index=index, columns=col)print(df)"""a b c de-07-01 1 3 3 5 4.0-07-02 11 7 15 13 9.1-07-03 4 2 7 9 3.5-07-04 15 11 12 6 11.1"""dict_demo1 = {key_ind: [] for key_ind in index}print(dict_demo1)"""{'-07-02': [], '-07-04': [], '-07-01': [], '-07-03': []}"""dict_demo2 = {key_ind: {key_col: df.loc[key_ind, key_col] for key_col in col} for key_ind in index}print(dict_demo2)"""{'-07-04': {'c': 12.0, 'd': 6.0, 'b': 11.0, 'a': 15.0, 'e': 11.1},'-07-03': {'c': 7.0, 'd': 9.0, 'b': 2.0, 'a': 4.0, 'e': 3.5},'-07-02': {'c': 15.0, 'd': 13.0, 'b': 7.0, 'a': 11.0, 'e': 9.0999999999999996},'-07-01': {'c': 3.0, 'd': 5.0, 'b': 3.0, 'a': 1.0, 'e': 4.0}}"""
（二）添加一组键值对
d[key] = valued.setdefault(self, k, d=None)demo：
# !/usr/bin/python2.7# -*- coding:utf-8 -*-"""@author: tz_zs"""keys = ['a', 'b', 'c']mydict = {key: "value_%s" % key for key in keys}print(mydict) # {'a': 'value_a', 'c': 'value_c', 'b': 'value_b'}mydict["d"] = "dddd"print(mydict) # {'a': 'value_a', 'c': 'value_c', 'b': 'value_b', 'd': 'dddd'}# d.setdefault 如果键存在，则和get()一样获取对应值，如果键不存在于字典中，将会添加键并将值设为defaultprint(mydict.setdefault("d", "ddddset")) # ddddprint(mydict) # {'a': 'value_a', 'c': 'value_c', 'b': 'value_b', 'd': 'dddd'}print(mydict.setdefault("e", "eeeeset")) # eeeesetprint(mydict) # {'a': 'value_a', 'c': 'value_c', 'b': 'value_b', 'e': 'eeeeset', 'd': 'dddd'}
（三）更新键值对
# !/usr/bin/python2.7# -*- coding:utf-8 -*-"""@author: tz_zs"""d = {"a": 1, 'b': 2, 'c': {'cc': 3, 'cc2': 4}}print(d)# {'a': 1, 'c': {'cc': 3, 'cc2': 4}, 'b': 2}d.update({"cc": 44})print(d)# {'a': 1, 'cc': 44, 'c': {'cc': 3, 'cc2': 4}, 'b': 2}d.update({"c": {"cc": 44}})print(d)# {'a': 1, 'cc': 44, 'c': {'cc': 44}, 'b': 2}
（四）删除一组键值对、清空字典等
删除一项： del d[key]d.pop(key) 返回pop掉的键值对的值 清空所有条目：d.clear()删除字典：del d# !/usr/bin/python2.7# -*- coding:utf-8 -*-"""@author: tz_zs"""keys = ['a', 'b', 'c']mydict = {key: "value_%s" % key for key in keys}print(mydict) # {'a': 'value_a', 'c': 'value_c', 'b': 'value_b'}del mydict["b"]print(mydict) # {'a': 'value_a', 'c': 'value_c'}mydict.clear()print(mydict) # {}del mydictprint(mydict)"""Traceback (most recent call last):File "/home/zmate/tzzs/mytz/test.py", line 19, in <module>print(mydict)NameError: name 'mydict' is not defined"""
（五）查询、取值
（1）获取一个 key 所对应的 value
d[key]d.get(key)d.get(key，default) 在当字典中没有相应的key时，返回 default（默认为None），而不是直接报错。#!/usr/bin/python2.7# -*- coding:utf-8 -*-"""@author: tz_zs"""keys = ['a', 'b', 'c', 'd', 'e']mydict = {key: "value_%s" % key for key in keys}print(mydict)"""{'a': 'value_a', 'd': 'value_d', 'c': 'value_c', 'e': 'value_e', 'b': 'value_b'}"""print(mydict.get("a")) # value_aprint(mydict["a"]) # value_a# print(mydict["aaa"]) # KeyError: 'aaa'print(mydict.get("aaa")) # Noneprint(mydict.get("aaa", {})) # {}print(mydict.get("aaa", {}).get("aaa", {})) # {}
（2）查询 key/value 是否在字典中
key是否在字典中：key in d
key in d.keys()values是否在字典中：
vaule in d.values()
#!/usr/bin/python2.7# -*- coding:utf-8 -*-"""@author: tz_zs"""keys = ['a', 'b', 'c', 'd', 'e']mydict = {key: "value_%s" % key for key in keys}print(mydict) # {'a': 'value_a', 'd': 'value_d', 'c': 'value_c', 'e': 'value_e', 'b': 'value_b'}# 查询是否在字典的key中print("a" in mydict) # Trueprint("a" in mydict.keys()) # Trueprint("f" in mydict) # Falseprint("value_a" in mydict) # False# 查询是否在字典的value中print("value_a" in mydict.values()) # True
（3）遍历字典
# 遍历所有的key：for key in d.keys():print(key)# 遍历所有的value：for value in d.values():print(value)# 遍历所有的键值对：for item in d.items():print(items) # 输出的是元组格式# 或者for k,v in d.items():print(k,"----",v)
#!/usr/bin/python2.7# -*- coding:utf-8 -*-"""@author: tz_zs"""keys = ['a', 'b', 'c', 'd', 'e']mydict = {key: "value_%s" % key for key in keys}print(mydict) # {'a': 'value_a', 'd': 'value_d', 'c': 'value_c', 'e': 'value_e', 'b': 'value_b'}for k in mydict.keys():print(k)"""bdeac"""for v in mydict.values():print(v)"""value_bvalue_dvalue_evalue_avalue_c"""for item in mydict.items():print(item)"""('b', 'value_b')('d', 'value_d')('e', 'value_e')('a', 'value_a')('c', 'value_c')"""for k, v in mydict.items():print(k, "----", v)"""b ---- value_bd ---- value_de ---- value_ea ---- value_ac ---- value_c"""
在Python中，检查一个元素是否在 dicitonary 或 set 中存在的效率很高。因为 dict 和 set 使用哈希表来实现。查找效率可以达到 O(1)。如果需要经常检查成员，建议使用 set 或 dict 。
（六）复制 d.copy
d.copy() 返回一个 dict 的浅复制
# -*- coding:utf-8 -*-"""@author: tz_zs"""mydict = {"china": {"shanghai": {"person1": {"age": 20, "data": [77, 87, 99]}},}}print(mydict) # {'china': {'shanghai': {'person1': {'age': 20, 'data': [77, 87, 99]}}}}mycopy = mydict.copy()mydict["china"] = 111print(mydict) # {'china': 111}print(mycopy) # {'china': {'shanghai': {'person1': {'age': 20, 'data': [77, 87, 99]}}}}mydict = {"china": {"shanghai": {"person1": {"age": 20, "data": [77, 87, 99]}},}}print(mydict) # {'china': {'shanghai': {'person1': {'age': 20, 'data': [77, 87, 99]}}}}mycopy = mydict.copy()mydict["china"]["shanghai"] = 111print(mydict) # {'china': {'shanghai': 111}}print(mycopy) # {'china': {'shanghai': 111}}
如需深层复制 dict，可使用 copy.deepcopy()
# -*- coding:utf-8 -*-"""@author: tz_zs"""import copymydict = {"china": {"shanghai": {"person1": {"age": 20, "data": [77, 87, 99]}},}}print(mydict) # {'china': {'shanghai': {'person1': {'age': 20, 'data': [77, 87, 99]}}}}mycopy = copy.deepcopy(mydict)mydict["china"] = 111print(mydict) # {'china': 111}print(mycopy) # {'china': {'shanghai': {'person1': {'age': 20, 'data': [77, 87, 99]}}}}mydict = {"china": {"shanghai": {"person1": {"age": 20, "data": [77, 87, 99]}},}}print(mydict) # {'china': {'shanghai': {'person1': {'age': 20, 'data': [77, 87, 99]}}}}mycopy = copy.deepcopy(mydict)mydict["china"]["shanghai"] = 111print(mydict) # {'china': {'shanghai': 111}}print(mycopy) # {'china': {'shanghai': {'person1': {'age': 20, 'data': [77, 87, 99]}}}}
（七）比较两个字典 cmp(x, y)
内置函数 cmp(x, y)
比较 x，y 两个参数，x < y 时返回值为 -1，x > y 时返回值为 1，x == y 时返回值为 0。
d1 = {"a": 2, "b": 4}d2 = {"a": 2, "b": 5}d3 = {"a": 2, "b": 3}print(cmp(d1, d1)) # 0print(cmp(d1, d2)) # -1print(cmp(d1, d3)) # 1
（八）参考：
/3/library/stdtypes.html#mapping-types-dict
