How to convert a list to a dictionary with indexes as values?

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Method 1

You can get the indices of a list from the built-in enumerate. You just need to reverse the index-value map and use a dictionary comprehension to create a dictionary:

>>> lst = ['A', 'B', 'C']
>>> {k: v for v, k in enumerate(lst)}
{'A': 0, 'C': 2, 'B': 1}

Method 2

Use built-in functions dict and zip:

>>> lst = ['A', 'B', 'C']
>>> dict(zip(lst, range(len(lst))))

Method 3

Python dict constructor has an ability to convert list of tuple to dict, with key as first element of tuple and value as second element of tuple. To achieve this you can use builtin function enumerate which yield tuple of (index, value).

However question’s requirement is exact opposite i.e. tuple should be (value, index). So this requires and additional step to reverse the tuple elements before passing to dict constructor. For this step we can use builtin reversed and apply it to each element of list using map

>>> lst = ['A', 'B', 'C']
>>> dict(map(reversed, enumerate(lst)))
>>> {'A': 0, 'C': 2, 'B': 1}

Method 4

You can also take advantage of enumerate:

your_list = ['A', 'B', 'C']
your_dict = {key: i for i, key in enumerate(your_list)}

Method 5

The easiest solution I used was:

lst = list('ABC')
dict(enumerate(lst))

edit: This is the reverse of what the author needed and exactly what I needed

Method 6

You have to convert the unhashable list into a tuple:

dct = {tuple(key): idx for idx, key in enumerate(lst)}

Method 7

If the elements in target list are unique, then a dict comprehension should be enough and elegant, just like the accepted answer.
```
>>> lst = ['A', 'B', 'C']
>>> pos_map = {ele: pos for pos, ele in enumerate(lst)}
```

But if there were duplicated elements in target list, then we could use the handy defaultdict in collections module:

>>> lst = ['A', 'B', 'C', 'A', 'A', 'B']
>>> from collections import defaultdict
>>> pos_map = defaultdict(list)
>>> for pos, ele in enumerate(lst):
>>>     pos_map[ele].append(pos)
>>>
>>> pos_map
>>> defaultdict(list, {'A': [0, 3, 4], 'B': [1, 5], 'C': [2]})

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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