为什么不能在打印后从枚举数据集创建字典？

Question

我在练习 enumerate() 和 python 中的词典。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？

当我没有打印出我的枚举数据时：

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 returns an iterator. An iterator may only be iterated over once.

一个常见的解决方案是使用itertools.tee到return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

为什么不能在打印后从枚举数据集创建字典？

Why can you not create a dictionary from an enumerated data set after you print it?

python

iterator

enumerate

python-3.x