Why does python product incorrect values with dictionary-CodePudding

I'm trying to produce a python dictionary that results in the following:

{'student_1': [{2017: 3}, {2018: 4}], 'student_2': [{2017: 60}, {2021: 153}], 'student_3': [{2015: 45}]}

The data comes from a database table that is tabular and looks like this:

| yearfiled | count | name      |
| 2017      | 3     | student_1 |
| 2018      | 4     | student_1 |
| 2017      | 60    | student_2 |
| 2021      | 153   | student_2 |
| 2015      | 45    | student_3 |

I can produce the desired formatted dictionary, however, each key in the dictionary is getting the values replaced with the last key's values in the database table.

    # chartdata is a fetchall() from a executed database query
    q={}
    for a,b,c in chartdata:
        v=[]
        q[a]=b
        v.append(q)
        datasetnew[c] = v

# Results
{'student_1': [{2015: 45}], 'student_2': [{2015:45}], 'student_3': [{2015:45}]}

I'm a bit perplexed on how to solve this. Any thoughts?

I tried a few different lines of code, however, none produced the correct results.

For example, this change put ALL the values for each student in every students key.

    v=[]
    q={}
    for a,b,c in chartdata:

        q[a]=b
        v.append(q)
        datasetnew[c] = v

CodePudding user response：

You can achieve this more easily with defaultdict:

from collections import defaultdict

datasetnew = defaultdict(list)
for year, count, name in chartdata:
    datasetnew[name].append({ year: count })

Result is:

{
    'student_1': [{2017: 3}, {2018: 4}], 
    'student_2': [{2017: 60}, {2021: 153}], 
    'student_3': [{2015: 45}]
}

However, I wonder why you would create lists of dictionaries that each only have one key? It would seem more useful to combine those little dictionaries into one dictionary per student:

datasetnew = defaultdict(dict)
for year, count, name in chartdata:
    datasetnew[name][year] = count

This produces this structure:

{
    'student_1': {2017: 3, 2018: 4}, 
    'student_2': {2017: 60, 2021: 153}, 
    'student_3': {2015: 45}
}