TypeError: unhashable type: 'dict' when attempting to hash list - advice sought

[MRAB]

On 2015-08-30 17:31, kbtyo wrote:
> On Saturday, August 29, 2015 at 10:50:18 PM UTC-4, MRAB wrote:
>> On 2015-08-30 03:05, kbtyo wrote:
>> > I am using Jupyter Notebook and Python 3.4. I have a data structure in the format, (type list):
>> >
>> > [{'AccountNumber': N,
>> > 'Amount': '0',
>> >   'Answer': '12:00:00 PM',
>> >    'ID': None,
>> >    'Type': 'WriteLetters',
>> >    'Amount': '10',
>> >    {'AccountNumber': Y,
>> >        'Amount': '0',
>> >        'Answer': ' 12:00:00 PM',
>> >         'ID': None,
>> >        'Type': 'Transfer',
>> >        'Amount': '2'}]
>> >
>> > The end goal is to write this out to CSV.
>> >
>> > For the above example the output would look like:
>> >
>> > AccountNumber, Amount, Answer, ID, Type, Amount
>> > N,0,12:00:00 PM,None,WriteLetters,10
>> > Y,2,12:00:00 PM,None,Transfer,2
>> >
>> > Below is the function that I am using to write out this data structure. Please excuse any indentation formatting issues. The data structure is returned through the function "construct_results(get_just_xml_data)".
>> >
>> > The data that is returned is in the format as above. "construct_headers(get_just_xml_data)" returns a list of headers. Writing out the row for "headers_list" works.
>> >
>> > The list comprehension "data" is to maintain the integrity of the column headers and the values for each new instance of the data structure (where the keys in the dictionary are the headers and values - row instances). The keys in this specific data structure are meant to check if there is a value instance, and if there is not - place an ''.
>> >
>> > def write_to_csv(results, headers):
>> >
>> >      headers = construct_headers(get_just_xml_data)
>> >      results = construct_results(get_just_xml_data)
>> >      headers_list = list(headers)
>> >
>> >      with open('real_csv_output.csv', 'wt') as f:
>> >          writer = csv.writer(f)
>> >          writer.writerow(headers_list)
>> >          for row in results:
>> >              data = [row.get(index, '') for index in results]
>> >          writer.writerow(data)
>> >
>> >
>> >
>> > However, when I run this, I receive this error:
>> >
>> > ---------------------------------------------------------------------------
>> > TypeError                                 Traceback (most recent call last)
>> > <ipython-input-747-7746797fc9a5> in <module>()
>> > ----> 1 write_to_csv(results, headers)
>> >
>> > <ipython-input-746-c822437eeaf0> in write_to_csv(results, headers)
>> >        9         writer.writerow(headers_list)
>> >       10         for item in results:
>> > ---> 11             data = [item.get(index, '') for index in results]
>> >       12         writer.writerow(data)
>> >
>> > <ipython-input-746-c822437eeaf0> in <listcomp>(.0)
>> >        9         writer.writerow(headers_list)
>> >       10         for item in results:
>> > ---> 11             data = [item.get(index, '') for index in results]
>> >       12         writer.writerow(data)
>> >
>> > TypeError: unhashable type: 'dict'
>> >
>> >
>> > I have done some research, namely, the following:
>> >
>> > https://mail.python.org/pipermail//tutor/2011-November/086761.html
>> >
>> > http://stackoverflow.com/questions/27435798/unhashable-type-dict-type-error
>> >
>> > http://stackoverflow.com/questions/1957396/why-dict-objects-are-unhashable-in-python
>> >
>> > However, I am still perplexed by this error. Any feedback is welcomed. Thank you.
>> >
>> You're taking the index values from 'results' instead of 'headers'.
>
> Would you be able to elaborate on this? I partially understand what you mean. However, each dictionary (of results) has the same keys to map to (aka, headers when written out to CSV). I am wondering if you would be able to explain how the index is being used in this case?
>
In the list comprehension on line 11, you have "item.get(index, '')".

What is 'index'?

You have "for index in results" in the list comprehension, and 'results' 
is a list of dicts, therefore 'index' is a _dict_.

That means that you're trying to look up an entry in the 'item' dict
using a _dict_ as the key.

Oh, and incidentally, line 12 should be indented to the same level as
line 11.