如何在字典（Python）中存储字符串中元素的位置？

Question

I want to get all the positions (indexes) of an element in a string and store them in a dictionary.

This is what I've tried:

string = "This is an example"       
test = {letter: pos for pos, letter in enumerate(string)}

But this only gives the last position of the letter. I'd like all positions, desired output:

test["a"]
{8, 13}

Answer 1

At the moment you are overwriting the dictionary values. For example,

>>> my_dict = {}
>>> my_dict['my_val'] = 1 # creating new value
>>> my_dict
{'my_val': 1}
>>> my_dict['my_val'] = 2 # overwriting the value for `my_val`
>>> my_dict
{'my_val': 2}

If you want to keep all values for a key you can use a list along with dict.setdefault method.

>>> print(dict.setdefault.__doc__)
Insert key with a value of default if key is not in the dictionary.
Return the value for key if key is in the dictionary, else default.
>>>
>>> result = {}
>>> string = "This is an example"
>>> 
>>> for index, value in enumerate(string):
...     result.setdefault(value, []).append(index)
... 
>>> result["a"]
[8, 13]

Answer 2

FOR LIST

Creating a dictionary with the keys being the characters in the input_string and the characters being the

indices of the characters in the input_string.

output = {}

Creating a input_string variable called input_string and assigning it the character "This is an example"

input_string = "This is an example"

Iterating through the input_string and assigning the index of the character to index and the character

to character .

output.setdefault(character, []) is checking if the key character exists in the dictionary output . If it does not exist, it will create the key character and assign it the character [] . If it does exist, it will return the character of the key character . Then, .append(index) will append the character of index to the character of the key character .

for index, character in enumerate(input_string):
    output.setdefault(character, []).append(index) 
   

Desired Output

output["i"]
[2, 5]

---

In SORT CODE BE LIKE:-

output = {}

input_string = "This is an example"

for index, character in enumerate(input_string):
    output.setdefault(character, []).append(index) 
   

FOR DICT/SET

---

Creating a dictionary with the keys being the characters in the input string and the values being

the indices of the characters in the input string.

output = {}

input_string = "This is an example"

for index, character in enumerate(input_string):
    output.setdefault(character, set()).add(index)