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

Question

I was practising with enumerate() and dictionaries in python. When I do not print out the enumerated data I am able to create a dictionary from the enumerated data. But when I do print out the enumerated data, I am no longer able to create a dictionary. Why would that be?

For when I do not print out my enumerated data:

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))

My output is

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

But when I do not:

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))

I get:

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

Asked By: Matthew Vedua

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Source

Answer 1

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

A common solution is to use itertools.tee to return an arbitrary number of independent iterators:

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

Answered By: jpp

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

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