json.dump() gives me "TypeError: keys must be a string"

Question

I have some very simple code that takes a dictionary with a tuple as a key and turns it into json:

In [11]:

import simplejson as json
In [12]:

data = {('category1', 'category2'): 4}
In [13]:

json.dumps(data)

However, running the code gives me:

TypeError: keys must be a string

I have tried str()'ing the keys and everything else I can find, but without luck.

Answer 1

The error seems pretty clear: Your keys must be strings.

If I take the example from your question and str()-ify the keys:

>>> data = {str(('category1', 'category2')): 4}

It works just fine:

>>> json.dumps(data)
'{"(\'category1\', \'category2\')": 4}'

Having said that, in your position I would consider making your keys more readable. Possibly something like:

>>> data = dict((':'.join(k), v) for k,v in data.items())

This turns a key like ('category1', 'category2') into category1:category2,