python - Subtract values from list of dictionaries from another list of dictionaries -

i have 2 lists of dictionaries.

foo = [{'tom': 8.2}, {'bob': 16.7}, {'mike': 11.6}] bar = [{'tom': 4.2}, {'bob': 6.7}, {'mike': 10.2}] 

the subtraction of , b should updated in foo:

foo = [{'tom': 4.0}, {'bob': 10.0}, {'mike': 1.4}] 

now tried 2 loops , zip-function:

def sub(a,b):            mydict,mydictcorr in zip(a,b):         {k:[x-y x, y in mydict[k], mydictcorr[k]] k in mydict}     return mydict print sub(foo,bar) 

i typeerror: 'float' object not iterable. where's mistake?

you close. issue list comprehension had in dictionary comprehension. mydict[k], mydictcorr[k] both returning floats, trying iterate on them [x-y x, y in mydict[k], mydictcorr[k]].

this work you:

def sub(base, subtract):     corrected = []     base_dict, sub_dict in zip(base, subtract):         corrected.append({k: v - sub_dict.get(k, 0) k, v in base_dict.items()})     return corrected 

or less readable one-liner (because wanted see if could):

def sub(base, subtract):     return [{k: v - sub_dict.get(k, 0) k, v in base_dict.items()} base_dict, sub_dict in zip(base, subtract)] 

having said that, may still see weird results when subtract floats. eg, {'tom': 3.999999999999999}. may want wrap v - sub_dict.get(k, 0) in call round.