How to add to python dictionary without replacing

Question

the current code I have is category1[name]=(number) however if the same name comes up the value in the dictionary is replaced by the new number how would I make it so instead of the value being replaced the original value is kept and the new value is also added, giving the key two values now, thanks.

Answer 1

You would have to make the dictionary point to lists instead of numbers, for example if you had two numbers for category cat1:

categories["cat1"] = [21, 78]

To make sure you add the new numbers to the list rather than replacing them, check it's in there first before adding it:

cat_val = # Some value
if cat_key in categories:
    categories[cat_key].append(cat_val)
else:
    # Initialise it to a list containing one item
    categories[cat_key] = [cat_val]

To access the values, you simply use categories[cat_key] which would return [12] if there was one key with the value 12, and [12, 95] if there were two values for that key.

Note that if you don't want to store duplicate keys you can use a set rather than a list:

cat_val = # Some value
if cat_key in categories:
    categories[cat_key].add(cat_val)
else:
    # Initialise it to a set containing one item
    categories[cat_key] = set(cat_val)