1.2 使用字典对象

准备工作

• 学习使用脚本计算词频，也就是每个词在文本中出现的次数。

操作方法

sentence = "Peter Piper picked a peck of pickled peppers A peck of pickled \                peppers Peter Piper picked If Peter Piper a peck of picked\                peppers Wheres the peck of pickled peppers Peter Piper Picked"word_dict = {}for word in sentence.split():    if word not in word_dict:        word_dict[word] = 1    else:        word_dict[word] += 1for key, value in word_dict.items():    print("{}:  {}".format(key, value))#print(word_dict)

输出结果如下：

Peter:  114Piper:  114picked:  113a:  112peck:  114of:  114pickled:  113peppers:  114A:  111If:  111Wheres:  111the:  111Picked:  111

工作原理：

• 字典的内容是一个键值对，这里的键是词，对应的值是出现的词频。
• item()函数可以遍历字典中的所有键值对。

更多内容：defaultdict

• python中的collection模块，有一个defaultdict类，它会传递一个函数作为参数，使用函数的返回值来初始化字典的未遇到的键.
• 可以看下面一个实例，它接受了num()函数的返回值作为默认初始值，这里的输出结果是上面的输出结果加上110。
• 另外，一般也可以使用python自带的int函数或者float函数。

from collections import defaultdictdef num():    return 110sentence = "Peter Piper picked a peck of pickled peppers A peck of pickled \                peppers Peter Piper picked If Peter Piper a peck of picked\                peppers Wheres the peck of pickled peppers Peter Piper Picked"word_dict = defaultdict(num)for word in sentence.split():    word_dict[word] += 1for key, value in word_dict.items():    print("{}:  {}".format(key, value))

更多内容：Counter子类

• 还可以用COunter来计算词频，它是一个字典子类，得到的结果也是一个字典类型。

from collections import Countersentence = "Peter Piper picked a peck of pickled peppers A peck of pickled \                peppers Peter Piper picked If Peter Piper a peck of picked\                peppers Wheres the peck of pickled peppers Peter Piper Picked"words = sentence.split()word_count = Counter(words)for key, value in word_dict.items():    print("{}:  {}".format(key, value))#print(word_count)