python updating dictionary with list as the value type

Question

I'm trying to iterate through data extracted from a file and store them in a dictionary based on each data's id

These are the id (str) for the data : "sensor", "version", "frame", "function"

And the data are in hexadecimal string.

What I bascially start with is a huge list of tuples in a form of id and data (that i extracted from a file)

example_list = [("sensor", 245), ("frame", 455), ("frame", 77)] and so on

This example_list stores all the data, so it has information of data for all the id.
I want to make a dictionary with id as key and list of data as value so when done iterating through the example_list, I have list of values for specific id (so I can iterate through the value list to get all the data for a specific id (the key))

To start, all values (list) will start with an empty list

my_dict = {"sensor": [], "frame": [], "version": [], "function": []}

Then, as I iterate through example_list, if the id is in my_dict as a key, I append the value to the values list in my_dict

for itm in example_list:
    if itm[0] in my_dict:
        tmp = my_dict[itm[0]] # since itm[0] is the id
        tmp.append(itm[1])
        my_dict[itm[0]] = tmp # update the list 

When I tried this, it seems like the final my_dict's value list has the value of the lastest data What I mean by this is if

example_list = [("sensor", 245), ("frame", 455), ("frame", 77)] 

then

my_dict = {"sensor": [245], "frame": [77], "version": [], "function": []}

I may be wrong about this interpretation (since the data I'm reading is really big), but when I printed my_dict in the end of function, each value list had only one data inside, which is far off from what I expected (list of data instead of just one)

I tried searching and people used update function to update the dictionary but that one also didn't seem to work and gave me somehting unhashable error/warning.

Any way to implement what I want to do?

Answer 1

try doing it like so:

for itm in example_list:
    if itm[0] in my_dict:
        my_dict[itm[0]].append(itm[1])

Answer 2

Your code is working as required. To simplify, as you've already instantiated the dict with empty lists:

for i,j in example_list:
    my_dict[i].append(j)
print(my_dict)

Output:

{'sensor': [245], 'frame': [455, 77], 'version': [], 'function': []}

Answer 3

What you want to do is:

for itm in example_list:
    if itm[0] in my_dict.keys(): # have to look if keys match
        my_dict[itm[0]].append(itm[1]) # # directly access the key-value pair

Your problem was that you created a new list and appended your item to it each time the loop was run, therefore the old data was deleted everytime.