准备工作操作方法工作原理更多内容defaultdict更多内容Counter子类
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] +=
1
for key, value
in word_dict.items():
print(
"{}: {}".format(key, value))
输出结果如下：
Peter:
114
Piper:
114
picked:
113
a:
112
peck:
114
of:
114
pickled:
113
peppers:
114
A:
111
If:
111
Wheres:
111
the:
111
Picked:
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 defaultdict
def num():
return 110
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 = defaultdict(num)
for word
in sentence.split():
word_dict[word] +=
1
for 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 Counter
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"
words = sentence.split()
word_count = Counter(words)
for key, value
in word_dict.items():
print(
"{}: {}".format(key, value))
