【Python】字典 - Dictionary

函数	内容
keys()	输出字典中的所有键
values()	输出字典中的所有值
items()	以元组的形式输出键值对
get()	获取字典中指定键的值

keys()

test = {'chuck':1, 'fred':42, 'jan':100}
print(test.keys())
if "chuck" in test.keys():print("true")

keys() 方法将字典 test 中所有的键输出；
输出结果为：

dict_keys(['chuck', 'fred', 'jan'])
true

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values()

test = {'chuck':1, 'fred':42, 'jan':100}
print(test.values())
if 1 in test.values():print("true")

values() 方法将字典 test 中所有的值输出；
输出结果为：

dict_values([1, 42, 100])
true

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items()

test = {'chuck':1, 'fred':42, 'jan':100}
print(test.items())
for k, v in test.items():print("key =", k, "while values =", v)

items() 方法将字典 test 中的键值对输出；
输出结果为：

dict_items([('chuck', 1), ('fred', 42), ('jan', 100)])
key = chuck while values = 1
key = fred while values = 42
key = jan while values = 100

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get()

inventory = {"apples":430, "banana":312, "pears":223, "oranges":221}print(inventory["banana"])
print(inventory.get("banana"))
print(inventory.get("banana",0))

get() 方法获取字典中指定键的值；
上述三种获取方法结果相同，而最后一种在找不到指定键的时候不会报错退出，而是会输出指定值，在这里是 0

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获取文件中指定字符的个数

方法一：统计单个元素的个数

f = open('scarlet.txt', 'r')
txt = f.read()t_count = 0
for c in txt:if c == 't':t_count = t_count + 1
print("t: " + str(t_count) + " occurrences")

方法二：统计多个元素的个数

f = open('scarlet.txt', 'r')
txt = f.read()letter_counts = {}
letter_counts['t'] = 0
letter_counts['s'] = 0
for c in txt:if c == 't':letter_counts[c] = letter_counts[c] + 1elif c == 's':letter_counts[c] = letter_counts[c] + 1print("t: " + str(letter_counts['t']) + " occurrences")
print("s: " + str(letter_counts['s']) + " occurrences")

方法三：统计所有元素的个数

f = open('scarlet.txt', 'r')
txt = f.read()letter_counts = {}
for c in txt:if c not in letter_counts:letter_counts[c] = 0letter_counts[c] = letter_counts[c] + 1print("t: " + str(letter_counts['t']) + " occurrences")
print("s: " + str(letter_counts['s']) + " occurrences")

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进阶版：获取所有单词的频数

word_counts = {}for word in sentence.split():word_counts[word] = word_counts.get(word, 0) + 1

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进阶版：获取所有字符的频数

char_d = {}
for c in stri:char_d[c] = char_d.get(c, 0) + 1