Question

I am working on a function that convert a multi-level dictionary to a list of one-level dictionaries.

The logic seems right. But when I run it, the while loop runs infinity. I found the first time it went into the while loop, next_level.pop() was working. Starting from the second time of the while loop, the pop() function never remove the last item of next_level. I also tried to retrieve the last item by next_level[-1], and delete the last item by del next_level[-1]. But the result is the same. I think it could be related to the reference thing. Any idea?

def flat_dict(self, params):
    """convert a multi-level dictionary to a list of one-level dictionaries"""
    plist = next_level = []
    next_level.append(params)
    while next_level:
        current_level = temp_level = next_level.pop()
        for k, v in current_level.iteritems():
            if isinstance(v, dict):
                next_level.append(temp_level.pop(k))
                pk = [x for x in next_level[-1].keys() if x.endswith('_id')]
                temp_level[pk[0]] = next_level[-1][pk[0]]
        plist.append(temp_level)
    return plist

Answer 1

Without an example of the dictionary, its a little hard to visualize…but generally for a case like this, I’d recommend recursion anyway:

def flatten( data ):
    output = []
    if ( isinstance(data, dict) ):
        output.append(data)
        for value in data.values():
            output += flatten(value)
    return output

In direct answer to your question tho, I’m not 100% sure what is going wrong – I can say that pop() itself will work just fine. I’m guessing it has to do with the way you’re initializing the plist, are you getting an infinite loop?

plist = next_level = []

This line is actually setting plist and next_level to the same exact list – not initializing a blank list for each variable.

>>> plist = next_level = []
>>> plist.append(1)
>>> next_level
[1]

When you modify plist, later in your loop, you’re actually modifying the next_level also which is not what is intended is my guess…try defining your plist/next_level this way:

plist = []
next_level = []

And see what happens.