Question

我正在使用enumerate()和python词典进行练习。当我不打印出枚举数据时，我能够从枚举数据创建字典。但是当我确实打印出枚举数据时，我将不再能够创建字典。为什么会这样？

当我不打印枚举数据时：

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

为什么在打印后无法从枚举数据集中创建字典？

1 个答案: