字典：反映对应关系的映射类型
- 字典（dict）是包含若干“键:值”元素的无序可变序列
- 字典中元素的“键”可以是python中任意不可变数据，例如整数、实数、复数、字符串、元组等类型可哈希数据，“键”不允许重复，“值”是可以重复的。字典在内部维护的哈希表使得检索操作非常快。
字典创建与删除
- 使用“=”
>>> aDict = {‘server‘:‘db.diveintopython3.org‘,‘database‘:‘mysql‘}>>> x = dict() # 创建空字典>>> x{}>>> y = {} # 创建空字典>>> keys = [‘a‘,‘b‘,‘c‘,‘d‘]>>> values = [1,2,3,4]>>> dictionary = dict(zip(keys,values)) # 根据已有数据创建字典>>> dictionary{‘a‘: 1, ‘b‘: 2, ‘c‘: 3, ‘d‘: 4}>>> d = dict(name = ‘Dong‘, age = 39) # 以关键参数的形式创建字典>>> d{‘name‘: ‘Dong‘, ‘age‘: 39}>>> aDict = dict.fromkeys([‘name‘,‘age‘,‘sex‘]) # 以给定内容为“键”，创建值为空的字典>>> aDict{‘name‘: None, ‘age‘: None, ‘sex‘: None}
字典推导式
- 使用字典推导式快速生成符合特定条件的字典
>>> {i:str(i) for i in range(1,5)}{1: ‘1‘, 2: ‘2‘, 3: ‘3‘, 4: ‘4‘}>>> x = [‘A‘,‘B‘,‘C‘,‘D‘]>>> y = [‘a‘,‘b‘,‘c‘,‘d‘]>>> {i:j for i,j in zip(x,y)}{‘A‘: ‘a‘, ‘B‘: ‘b‘, ‘C‘: ‘c‘, ‘D‘: ‘d‘}
字典元素的访问
- 字典中每个元素表示一种映射关系或对应关系
>>> aDict = {‘age‘:30,‘score‘:[98,97],‘name‘:‘Dong‘,‘sex‘:‘male‘}>>> aDic[‘age‘]>>> aDict[‘age‘]30>>> aDict[‘address‘] # 字典中不存在该key时，抛出异常Traceback (most recent call last): File "<stdin>", line 1, in <module>KeyError: ‘address‘# 处理异常方式一：>>> if ‘address‘ in aDict:... print(aDict[‘address‘])... else:... print(‘No Exists‘)...No Exists# 处理异常方式二：>>> try:... print(aDict[‘address‘])... except:... print(‘No Exist‘)...No Exist - get()方法：返回指定“键”的值，并且允许指定该键不存在时返回特定的“值”
>>> aDict.get(‘age‘)30>>> aDict.get(‘adress‘,‘No Exist.‘) # 指定键不存在时返回指定默认值‘No Exist.‘>>> import string>>> import random>>> x = string.ascii_letters + string.digits>>> z = ‘‘.join((random.choice(x) for i in range(1000)))>>> d = dict()>>> for ch in z: # 遍历字符串统计词频... d[ch] = d.get(ch,0) + 1...>>> for k,v in sorted(d.items()): # 查看统计结果... print(k,‘:‘,v)...0 : 131 : 192 : 173 : 174 : 195 : 256 : 217 : 128 : 179 : 17A : 11B : 20C : 15D : 21E : 22F : 9G : 15H : 12I : 9J : 16K : 13L : 16M : 19N : 14O : 17P : 11Q : 14R : 16S : 11T : 22U : 13V : 20W : 21X : 17Y : 14Z : 21a : 17b : 9c : 17d : 15e : 14f : 11g : 18h : 20i : 21j : 19k : 20l : 9m : 16n : 10o : 13p : 14q : 25r : 17s : 12t : 20u : 10v : 20w : 17x : 10y : 15z : 25
- setdefault()方法：用于返回指定“键”对应的值，如果字典中不存在该“键”，就添加一个新元素并设置该“键”对应的“值”（默认为None）
>>> aDict.setdefault(‘adress‘,‘SDIBT‘)‘SDIBT‘>>> aDict{‘age‘: 30, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> aDict.setdefault(‘age‘,23)30 - 对字典直接进行迭代或者遍历时默认是遍历字典的“键”
>>> aDict{‘age‘: 30, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> for item in aDict: # 默认遍历字典的“键”... print(item,end=‘ ‘)...age score name sex adress >>>>>> for item in aDict.items(): # 明确指定遍历字典的元素... print(item,end=‘ ‘)...(‘age‘, 30) (‘score‘, [98, 97]) (‘name‘, ‘Dong‘) (‘sex‘, ‘male‘) (‘adress‘, ‘SDIBT‘) >>>>>> aDict.items()dict_items([(‘age‘, 30), (‘score‘, [98, 97]), (‘name‘, ‘Dong‘), (‘sex‘, ‘male‘), (‘adress‘, ‘SDIBT‘)])>>> aDict.keys()dict_keys([‘age‘, ‘score‘, ‘name‘, ‘sex‘, ‘adress‘])>>> aDict.values()dict_values([30, [98, 97], ‘Dong‘, ‘male‘, ‘SDIBT‘])
元素的添加、修改与删除
- 当以指定“键”为下标为字典元素赋值时，该键存在表示修改，不存在表示添加
>>> aDict = {‘age‘: 30, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> aDict[‘age‘] = 39>>> aDict{‘age‘: 39, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> aDict[‘school‘] = ‘sichuandaxue‘>>> aDict{‘age‘: 39, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘, ‘school‘: ‘sichuandaxue‘} - update()方法可以将另外一个字典的“键:值”一次性全部添加到当前字典对象，如果两个字典中存在相同的“键”，则以另一个字典中的“值”为准对当前字典进行更新
>>> aDict = {‘age‘: 30, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> aDict.update({‘a‘: 87, ‘age‘:39})>>> aDict{‘age‘: 39, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘, ‘a‘: 87} - del命令删除字典中指定的元素
>>> aDict = {‘age‘: 30, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> del aDict[‘adress‘]>>> aDict{‘age‘: 30, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘}>>> del aDict>>> aDictTraceback (most recent call last): File "<stdin>", line 1, in <module>NameError: name ‘aDict‘ is not defined - 字典对象的pop()和popitem()方法可以弹出并删除指定的元素
>>> aDict = {‘age‘: 30, ‘score‘: [98, 97], ‘name‘: ‘Dong‘, ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> aDict.pop(‘name‘) # 弹出指定键对应的值‘Dong‘>>> aDict{‘age‘: 30, ‘score‘: [98, 97], ‘sex‘: ‘male‘, ‘adress‘: ‘SDIBT‘}>>> aDict.popitem() # 弹出一个元素(‘adress‘, ‘SDIBT‘)>>> aDict{‘age‘: 30, ‘score‘: [98, 97], ‘sex‘: ‘male‘}
标准库collections中与字典有关的类
- OrderedDict类
字典dict是无序的，如果需要一个可以记住元素插入顺序的字典，可以使用collections.OrderedDict
>>> import collections>>> x = collections.OrderedDict()>>> x[‘a‘] = 3>>> x[‘b‘] = 5>>> x[‘c‘] = 8>>> xOrderedDict([(‘a‘, 3), (‘b‘, 5), (‘c‘, 8)])
- defaultdict类
字母出现频次统计问题，也可以使用collections模块的defaultdict类来实现
>>> import string>>> import random>>> x = string.ascii_letters+string.digits+string.punctuation>>> z = ‘‘.join([random.choice(x) for i in range(100)])>>> from collections import defaultdict>>> frequences = defaultdict(int) # 所有值默认为0>>> frequencesdefaultdict(<class ‘int‘>, {})>>> for item in z:... frequences[item] += 1...>>> frequences.items()dict_items([(‘F‘, 1), (‘[‘, 2), (‘q‘, 1), (‘>‘, 2), (‘d‘, 5), (‘`‘, 1), (‘e‘, 2), (‘!‘, 3), (‘A‘, 1), (‘R‘, 1), (‘Z‘, 2), (‘V‘, 2), (‘g‘, 2), (‘n‘, 2), (‘2‘, 1), (‘w‘, 1), (‘|‘, 1), (‘v‘, 3), (‘c‘, 2), (‘u‘, 3), (‘&‘, 4), (‘m‘, 2), (‘S‘, 2), (‘,‘, 2), (‘@‘, 3), (‘$‘, 2), (‘{‘, 1), (‘j‘, 1), (‘\\‘, 1), (‘~‘, 1), (‘U‘, 1), (‘=‘, 1), (‘M‘, 4), (‘l‘, 1), (‘^‘, 1), (‘}‘, 1), (‘]‘, 2), (‘0‘, 1), (‘+‘, 2), (‘(‘, 1), (‘"‘, 1), (‘Q‘, 1), (‘4‘, 2), (‘.‘, 1), (‘x‘, 1), ("‘", 1), (‘<‘, 2), (‘/‘, 2), (‘;‘, 1), (‘E‘, 1), (‘)‘, 1), (‘o‘, 1), (‘P‘, 1), (‘W‘, 1), (‘B‘, 1), (‘K‘, 1), (‘8‘, 1), (‘_‘, 1), (‘N‘, 1), (‘h‘, 1), (‘7‘, 1), (‘I‘, 1), (‘G‘, 1), (‘*‘, 1), (‘y‘, 1)])创建defaultdict对象时，传递的参数表示字典中值的类型
>>> from collections import defaultdict>>> games = defaultdict(list)>>> gamesdefaultdict(<class ‘list‘>, {})>>> games[‘name‘].append(‘dong‘)>>> games[‘name‘].append(‘zhang‘)>>> games[‘score‘].append(90)>>> games[‘score‘].append(93)>>> gamesdefaultdict(<class ‘list‘>, {‘name‘: [‘dong‘, ‘zhang‘], ‘score‘: [90, 93]}) - Counter类
对于词频统计的问题，使用collections模块的Counter类可以更加快速地实现这个功能，并且能够提供更多的功能，例如，查找出现次数最多的元素
>>> import string>>> import random>>> x = string.ascii_letters+string.digits+string.punctuation>>> z = ‘‘.join([random.choice(x) for i in range(100)])>>> from collections import Counter>>> frequences = Counter(z)>>> frequences.items()dict_items([(‘H‘, 12), (‘%‘, 18), (‘K‘, 13), (‘A‘, 12), (‘\\‘, 6), (‘N‘, 11), (‘2‘, 14), (‘y‘, 13), (‘z‘, 12), (‘T‘, 10), (‘:‘, 8), (‘m‘, 8), ("‘", 11), (‘R‘, 12), (‘,‘, 10), (‘E‘, 7), (‘e‘, 16), (‘b‘, 10), (‘f‘, 16), (‘+‘, 8), (‘7‘, 15), (‘v‘, 9), (‘l‘, 15), (‘"‘, 9), (‘.‘, 12), (‘^‘, 20), (‘_‘, 16), (‘>‘, 7), (‘h‘, 12), (‘C‘, 12), (‘p‘, 13), (‘n‘, 8), (‘Y‘, 14), (‘L‘, 11), (‘O‘, 12), (‘{‘, 5), (‘3‘, 10), (‘)‘, 15), (‘}‘, 4), (‘|‘, 14), (‘a‘, 10), (‘@‘, 9), (‘w‘, 10), (‘B‘, 11), (‘6‘, 8), (‘Q‘, 11), (‘`‘, 10), (‘/‘, 8), (‘<‘, 5), (‘=‘, 12), (‘M‘, 12), (‘4‘, 6), (‘s‘, 18), (‘[‘, 7), (‘G‘, 12), (‘#‘, 16), (‘o‘, 13), (‘*‘, 8), (‘i‘, 16), (‘P‘, 12), (‘k‘, 17), (‘j‘, 4), (‘-‘, 15), (‘D‘, 4), (‘]‘, 6), (‘q‘, 16), (‘$‘, 17), (‘J‘, 15), (‘U‘, 14), (‘t‘, 11), (‘I‘, 11), (‘0‘, 7), (‘r‘, 12), (‘&‘, 6), (‘!‘, 12), (‘u‘, 10), (‘F‘, 9), (‘W‘, 6), (‘c‘, 11), (‘1‘, 8), (‘5‘, 6), (‘;‘, 5), (‘V‘, 12), (‘~‘, 10), (‘Z‘, 11), (‘d‘, 9), (‘9‘, 9), (‘X‘, 13), (‘8‘, 9), (‘?‘, 5), (‘S‘, 6), (‘x‘, 7), (‘(‘, 7), (‘g‘, 6)])>>> frequences.most_common(1) # 返回出现次数最多的一个字符及其词频[(‘^‘, 20)]>>> frequences.most_common(3)[(‘^‘, 20), (‘%‘, 18), (‘s‘, 18)]>>> frequences.most_common(10)[(‘^‘, 20), (‘%‘, 18), (‘s‘, 18), (‘k‘, 17), (‘$‘, 17), (‘e‘, 16), (‘f‘, 16), (‘_‘, 16), (‘#‘, 16), (‘i‘, 16)]>>> z = ‘‘.join([random.choice(x) for i in range(10000)])>>> frequences = Counter(z)>>> frequences.most_common(10)[(‘O‘, 127), (‘c‘, 125), (‘5‘, 121), (‘-‘, 121), (‘\\‘, 121), ("‘", 120), (‘~‘, 118), (‘,‘, 118), (‘J‘, 118), (‘<‘, 117)]?>>> z = [1,2,3,4,1,‘a‘,‘v‘,‘wer‘,‘wer‘,‘wer‘,1]>>> frequences = Counter(z)>>> frequences.most_common(3)[(1, 3), (‘wer‘, 3), (2, 1)]
原文地址：https://www.cnblogs.com/zxbdboke/p/10480203.html
时间： 2024-10-02 23:43:34