runtime error with python dictionary while using defaultdict

Question

I am using a dictionary to add key and values in it. I am checking if the key is already present, and if yes, I am appending the value; if not I add a key and the corresponding value.

I am getting the error message:

AttributeError: 'str' object has no attribute 'append'

Here is the code. I am reading a CSV file:

metastore_dir = collections.defaultdict(list)
with open(local_registry_file_path + data_ext_dt + "_metastore_metadata.csv",'rb') as metastore_metadata:
    for line in metastore_metadata: 
        key = line[2]
        key = key.lower().strip()
        if (key in metastore_dir):
            metastore_dir[key].append(line[0])
        else:
            metastore_dir[key] = line[0]

I found the answer on stack overflow which says to use defaultdict to resolve the issue, i am getting the error message even after the suggested anwer. I have pasted my code for reference.

possible duplicate of [Python creating a dictionary of lists](http://stackoverflow.com/questions/960733/python-creating-a-dictionary-of-lists) — TigerhawkT3, Aug 20 '15 at 20:36
i am using defaultdict and still getting the error, please review my code once. — Tanveer Ahmed, Aug 20 '15 at 20:47

score 0 · Answer 1 · answered Aug 20 '15 at 21:45

0

The str type has no append() method. Replace your call to append with the + operator:

sentry_dir[key] += line[1]

answered Aug 20 '15 at 21:45

Fernando Matsumoto

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this one is not working, key and value are jumbled up – Tanveer Ahmed Aug 20 '15 at 23:21
Can you give an example of expected input and output? – Fernando Matsumoto Aug 21 '15 at 00:29

score 0 · Answer 2 · answered Aug 21 '15 at 01:03

0

It is a dictionary of strings. To declare it as a list use

    if (key not in metastore_dir):  ## add key first if not in dict
        metastore_dir[key] = []  ## empty list
    metastore_dir[key].append(line[0])

    """ with defaultdict you don't have to add the key
        i.e. "if key in" not necessary
    """
    metastore_dir[key].append(line[0])

answered Aug 21 '15 at 01:03

Thanks for your reply – Tanveer Ahmed Aug 21 '15 at 15:52

score 0 · Answer 3 · answered Aug 22 '15 at 04:45

When you insert a new item into the dictionary, you want to insert it as a list:

...
if (key in metastore_dir):
    metastore_dir[key].append(line[0])
else:
    metastore_dir[key] = [line[0]] # wrapping it in brackets creates a singleton list

On an unrelated note, it looks like you are not correctly parsing the CSV. Trying splitting each line by commas (e.g. line.split(',')[2] refers to the third column of a CSV file). Otherwise line[0] refers to the first character of the line and line[2] refers to the third character of the line, which I suspect is not what you want.

runtime error with python dictionary while using defaultdict

3 Answers3