Python：向现有键字典添加另一个值

Question

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'}

ie 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?

Answer 1

The problem is that your values are sometimes strings (eg for Network ) and sometimes lists (eg 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']}

Answer 2

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']}

Answer 3

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)

Answer 4

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'}