python - Flatten dictionaries of list? -

using python 2.6.5, trying flatten lists attach each dictionary key , put them 1 list if possible 1 unique set. tried 2 different functions , not sure need do.

the problem i'm having it's not returning list of values list of keys.

for example:

dict = {'alpha': [[], ['dg1']],         'beta': [[], ['dg2'], ['dg3'], ['dg4'], ['dg1']],         'charlie': [[], ['dg1']],         'delta': [[], ['dg4']]}  new_list = flatten(dict) 

results in [alpha,beta,charile,delta], want [dg1,dg2,dg3,dg4].

what havve tried:

def flatten(a):     b = []     c in a:         if isinstance(c, list) , any(isinstance(i, list) in c):             b.extend(flatten(c))         else:             b.append(c)     return b  def flatten_list(lst):     """     utility flatten list of list.     if outer list not list or none, returns original object.     return none none.     """     if not isinstance(lst, list):         return lst     return sum(([x] if not isinstance(x, list) else flatten_list(x)                     x in lst), []) 

think logic in part of code:

if isinstance(c, list) , any(isinstance(i, list) in c):     b.extend(flatten(c)) else:     b.append(c) 

if c list without lists inside, you're going append onto b, instead of extending. so, if b = [0] , c = [1, 2], you'll end b = [0, [1, 2]].

you need always extend if c list. so, can this:

if isinstance(c, list):     if any(isinstance(i, list) in c):         b.extend(flatten(c))     else:         b.extend(c) else:     b.append(c) 

this work. think happens if call flatten on already-flat list, , should able simplify further.

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meanwhile, if don't know how flatten each value in dict, can explicit loop:

d = {'alpha': [[], ['dg1']], 'beta': [[], ['dg2'], ['dg3'], ['dg4'], ['dg1']], 'charlie': [[], ['dg1']], 'delta': [[], ['dg4']]} new_d = {} k, v in d.items():     new_d[k] = flatten(v) 

i've used d.items() there. in python 2.x, gives new list, key-value pairs dictionary. if dictionary huge, making list loop on can wasteful, may want use d.iteritems() instead, gives lazy iterator instead of list.

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if know comprehensions are, should recognize pattern of "create empty collection, loop, add collection" paradigm case converting comprehension:

new_d = {k: flatten(v) k, v in d.items()} 

unfortunately, dictionary comprehensions weren't added until 2.7. can same effect dict function , generator expression:

new_d = dict((k, flatten(v)) k, v in d.items()) 

not quite readable, has same effect, , works 2.4.