python - 为什么打印后不能从枚举数据集创建字典？

Question

这个问题已经有答案了:

Why can't I iterate twice over the same iterator? How can I "reset" the iterator or reuse the data? (6 个回答)

已关闭 4 年前。

我正在和enumerate()一起练习和 python 中的字典。当我不打印枚举数据时，我可以根据枚举数据创建字典。但是当我打印出枚举数据时，我无法再创建字典。为什么会这样？

当我不打印我的枚举数据时:

data = ['a','b','c','d']

enum_data = enumerate(data, 1)

data_dict = dict(enum_data)
print("Data Dict: ", data_dict)

print("Should be 'a': ", data_dict.get(1))

我的输出是

Data Dict:  {1: 'a', 2: 'b', 3: 'c', 4: 'd'}
Should be 'a':  a

但是当我不这样做时:

data = ['a','b','c','d']

enum_data = enumerate(data, 1)
for enum, point in enum_data:
    print("Count: ", enum, " ", "Element: ", point)

data_dict = dict(enum_data)
print("Data Dict: ", data_dict)

print("Should be 'a': ", data_dict.get(1))

我得到:

Count:  1   Element:  a
Count:  2   Element:  b
Count:  3   Element:  c
Count:  4   Element:  d
Data Dict:  {}
Should be 'a':  None

Answer 1

enumerate返回一个迭代器。迭代器 may only be iterated over once .

常见的解决方案是使用 itertools.tee返回任意数量的独立迭代器:

from itertools import tee

data = ['a','b','c','d']

enum_data1, enum_data2 = tee(enumerate(data, 1), 2)
for enum, point in enum_data1:
    print("Count: ", enum, " ", "Element: ", point)

data_dict = dict(enum_data2)

print("Data Dict: ", data_dict)  # {1: 'a', 2: 'b', 3: 'c', 4: 'd'}
print("Should be 'a': ", data_dict.get(1))  # a