Can't append to dictionary

Question

I have a set of file extensions (.jpg, .png, .exe, etc.) in a set called set_of_files .

Below, I populate the keys of a dictionary from this set, while making the values None .

The variable line[2] contains the file size in bytes for each file extension.

My goal is to append line[2] as the value to each file extension in the dictionary, and then add up the total bytes.

ie '.jpg': [1, 3, 4, 5] -> '.jpg': [13]

However, I'm confused because I can't append to this dictionary (last line).

import re

# create set

set_of_files = set(list_of_files)

# populate dict

dicts = {key: None for key in list_of_files}

# go through and place total size by extension name

for line in open(file):

    line = re.split('\s+', line)

    for specific_line in set_of_files:

        if line[3].endswith(specific_line):

            dicts[specific_line].append(line[2])

Answer 1

You can't append it, because, you've initialised None as values for dictionary.

import re

# create set

set_of_files = set(list_of_files)

# populate dict
                 _________________________ "None" is assigned here
                |
               \|/
dicts = {key: None for key in list_of_files}

# go through and place total size by extension name

for line in open(file):

    line = re.split('\s+', line)

    for specific_line in set_of_files:

        if line[3].endswith(specific_line):

            dicts[specific_line].append(line[2])

Instead, initialise an empty list [] , like this...

import re

# create set

set_of_files = set(list_of_files)

# populate dict

dicts = {key: [] for key in list_of_files}

# go through and place total size by extension name

for line in open(file):

    line = re.split('\s+', line)

    for specific_line in set_of_files:

        if line[3].endswith(specific_line):

            dicts[specific_line].append(line[2])