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pythondictionary
Catherine
Catherine

Reputation: 747

Python: Adding another value to an existing key dictionary

I am trying to take in all the files at a given path, and order them based on my data title names. So my data title names are:

data_titles = ['CPU','Physical_Disk','Memory','Network']

The files at this given path are named like 'CPU_data.txt' and 'Memory_data.txt' but there are also some that have more than one file per data title for example 'Physical_Disk_data_1.txt' and 'Physical_Disk_data_2.txt'.

I am trying to create a dicitonary in the style of:

{'Network': 'Network_data.txt', 
 'Physical_Disk': ['Physical_Disk_data_1.txt','Physical_Disk_data_2.txt'], 
 'CPU': 'CPU_data.txt', 
 'Memory': 'Memory_data.txt'}

i.e not overwriting older values

However I keep getting the error AttributeError: 'dict' object has no attribute 'update', if I use append instead of update I get a similar error AttributeError: 'dict' object has no attribute 'append'

table_csv_files={}
    for file_names in os.listdir(Data_folder):
        for name in data_titles:
            if name in file_names:
                if name in table_csv_files:
                    table_csv_files[name].update(file_names)
                    # Have also tried table_csv_files.append({name:file_names})
                else:
                    table_csv_files[name]=file_names

                print table_csv_files

What am I doing wrong?

Upvotes: 1

Views: 5274

Answers (4)

terence hill
terence hill

Reputation: 3454

According to Python documentation it's better to use defaultdict(), see the answer by Moses Koledoye

You cannot append to a dictionary. You can append to a value corresponding to a key if that value is a list (or antoher object that implement the append method).

I think this is the best way to make the code easy to follow. The function setdefault add a new list only if the key is not present.

   if name in file_names:
        table_csv_files.setdefault(name, [])
        table_csv_files[name].append(file_names)

Upvotes: 0

Moses Koledoye
Moses Koledoye

Reputation: 78536

Use a defaultdict whose default value is an empty list, then you can append to the dictionary values without worrying about which keys already exist in your dictionary.

from collections import defaultdict

table_csv_files = defaultdict(list)

for file_names in os.listdir(Data_folder):
     for name in data_titles:
          if name in file_names:
                table_csv_files[name].append(file_names)

print table_csv_files 
# {'CPU': ['CPU_data.txt'], 'Memory': ['Memory_data_1.txt', 'Memory_data_2.txt'], 'Physical_Disk': ['Physical_Disk_data.txt'], 'Network': ['Network_data.txt']}

Upvotes: 2

Rajiv Sharma
Rajiv Sharma

Reputation: 7102

Dictionary[key] = new value

here is a simple example of how you can add/update another value to an existing key in dictionary.

my_dict = {'name': 'Rajiv Sharma', 'city': 'Delhi'}
print my_dict
my_dict['city'] = 'Kuala Lumpur'
print my_dict

output:

{'city': 'Delhi', 'name': 'Rajiv Sharma'}
{'city': 'Kuala Lumpur', 'name': 'Rajiv Sharma'}

Upvotes: -1

k-nut
k-nut

Reputation: 3575

The problem is that your values are sometimes strings (e.g. for Network) and sometimes lists (e.g. for Physical_Disk). If you make sure that they are always lists you can easily append to them:

data_titles = ['CPU','Physical_Disk','Memory','Network']
table_csv_files={}
listdir_output = ['Network_data.txt', 'Physical_Disk_data_1.txt','Physical_Disk_data_2.txt', 'CPU_data.txt', 'Memory_data.txt']
for file_names in listdir_output:
    for name in data_titles:
        if name in file_names:
            if name in table_csv_files:
                table_csv_files[name].append(file_names)
            else:
                table_csv_files[name] = [file_names]
print table_csv_files

Output:

{'Memory': ['Memory_data.txt'], 'Physical_Disk': ['Physical_Disk_data_1.txt', 'Physical_Disk_data_2.txt'], 'Network': ['Network_data.txt'], 'CPU': ['CPU_data.txt']}

Upvotes: 2

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