Places is a list and not a dictionary. This line below should therefore not work:

print(data['places']['latitude'])

You need to select one of the items in places and then you can list the place's properties. So to get the first post code you'd do:

print(data['places'][0]['post code'])

It is a bit lenghty, but in that example above:

In [1]: import json

In [2]: s = """\
   ...: {
   ...:   "A": {
   ...:     "B": {
   ...:       "unknown": {
   ...:         "1": "F",
   ...:         "maindata": [
   ...:           {
   ...:             "Info": "TEXT"
   ...:           }
   ...:         ]
   ...:       }
   ...:     }
   ...:   }
   ...: }"""

In [3]: data = json.loads(s)

In [4]: data['A']['B']['unknown']['maindata'][0]['Info']
Out[4]: u'TEXT'

You basically treat it as a dictionary, passing the keys to get the values of each nested dictionary. The only different part is when you hit maindata, where the resulting value is a list. In order to handle that, we pull the first element [0] and then access the Info key to get the value TEXT.

In the case of unknown changing, you would replace it with a variable that represents the 'known' name it will take at that point in your code:

my_variable = 'some_name'
data['A']['B'][my_variable]['maindata'][0]['Info']

And if I would have actually read your question properly the first time, if you don't know what unknown is at any point, you can do something like this:

data['A']['B'].values()[0]['maindata'][0]['Info']

Where values() is a variable containing:

[{u'1': u'F', u'maindata': [{u'Info': u'TEXT'}]}]

A single-item list that can be accessed with [0] and then you can proceed as above. Note that this is dependent on there only being one item present in that dictionary - you would need to adjust a bit if there were more.