如何更新字典以添加到 Python 中的列表

Question

If I have the dictionary

d = {
  "group1": [0],
  "group2": [3,7]
}

How can I update the list to add another value to it.

I thought

d.update({"group1": [4]})

would add the number 4 and that the new dictionary would be

{
  "group1": [0,4],
  "group2": [3,7]
}

but this is not the case when I try it.

Answer 1

d["group1"].append(4)

Answer 2

Just use the .append() method of the list. You can access d['group1'] and that is your list.

d['group1'].append(4)

Answer 3

If your goal is to update a dictionary by appending key:values from another one, you can do it like this:

d = { "group1": [0],
      "group2": [3,7],
      "group3": [8]
    }
u = { "group1": [4],
      "group2": [5,9],
      "group4": [1,2]
    }

d = { g:d.get(g,[]) + u.get(g,[]) for g in {*d,*u} }

# {'group1': [0, 4], 'group4': [1, 2], 'group2': [3, 7, 5, 9], 'group3': [8]}