Convert JSON from a webservice to text file
I am here for some criticism and learning :)


That's really a great attitude. Keep it up and you'll get far.

Handling the last item differently

You alluded to the issue of doing social treatment for the last item in a loop. There are two related relevant places in the posted code:

    for dictionary in list_of_dictionaries:
        for column in list_of_columns:
            # ...
            if column != list_of_columns[-1]:
                # special treatment 1
        if dictionary != list_of_dictionaries[-1]:
            # special treatment 2


Having a conditional statement that is executed for every item in a list, and you know it is false for all items except the last, is not pretty. It could be acceptable, if the condition is super fast, for example a simple comparison of two numbers. Here you are comparing strings and objects, which may not be super fast.

You could convert this to a simple numeric comparison by using a range loop, and then comparing indexes instead of objects.

You could also change the loops to iterate until the element before the end, and then do the special treatment for the last, outside the loop. That way you can eliminate the conditional statements.

Seeking in a file

When opening a file for writing with the w option only, there's no need to seek(0) in it, that will happen automatically, and the file will be rewritten.

Extracting the beginning of a string until some character

It's not efficient to use split for this. It will allocate a list to store the results, and scan until the end of the string, even though you only need the first part. It would be better to find the index of the dot, and then get a substring.