Update Dictionary By Incrementing

>>> D1 = {'potatoes':2.67,'sugar':1.98,'cereal':5.99,'crisps':1.09} >>> D2 = {'parsley':0.76,'cereal':3.22} >>> D1 = updateDictionaryByIncrementing(D1,

Solution 1:

You can use looping over the keys:

forkeyin D2:
    D1[key] = D1.get(key, 0) + D2[key]

or you can use collections.Counter() objects:

from collections import Counter

D1 = dict(Counter(D1) + Counter(D2))

Demo of the latter technique:

>>> from collections import Counter
>>> D1 = {'potatoes':2.67,'sugar':1.98,'cereal':5.99,'crisps':1.09} 
>>> D2 = {'parsley':0.76,'cereal':3.22} 
>>> Counter(D1) + Counter(D2)
Counter({'cereal': 9.21, 'potatoes': 2.67, 'sugar': 1.98, 'crisps': 1.09, 'parsley': 0.76})
>>> dict(Counter(D1) + Counter(D2))
{'cereal': 9.21, 'parsley': 0.76, 'sugar': 1.98, 'potatoes': 2.67, 'crisps': 1.09}

Solution 2:

Counter is a convenient way to do this (counts don't have to be integers)

>>> from collections import Counter
>>> D1 = {'potatoes':2.67,'sugar':1.98,'cereal':5.99,'crisps':1.09}
>>> D2 = {'parsley':0.76,'cereal':3.22} 
>>> Counter(D1) + Counter(D2)
Counter({'cereal': 9.21, 'potatoes': 2.67, 'sugar': 1.98, 'crisps': 1.09, 'parsley': 0.76})

You could also use dict.update list this:

>>> D1.update((k, D1.get(k, 0) + v) for k, v in D2.items())
>>> D1
{'potatoes': 2.67, 'parsley': 0.76, 'crisps': 1.09, 'cereal': 9.21, 'sugar': 1.98}

Solution 3:

If you want to increment the values of the dictionaries, you could implement updateDictionaryByIncrementing like this:

def updateDictionaryByIncrementing(a,b):
   c = dict()
   for k,v in b.items():
        c[k] = a.get(k,0.0) + v
   return c

By using the get method of the a dictionary, the case where a does not have a value with the given key is handled using a default value.

Solution 4:

You can use dictionary comprehension, like this

D1 = {'potatoes': 2.67, 'sugar': 1.98, 'cereal': 5.99, 'crisps': 1.09}
D2 = {'parsley': 0.76, 'cereal': 3.22}
print {key: D1.get(key, 0) + D2.get(key, 0) for key in D1.viewkeys() | D2}

Output

{'cereal': 9.21,
 'crisps': 1.09,
 'parsley': 0.76,
 'potatoes': 2.67,
 'sugar': 1.98}

Solution 5:

You can do that using try/except as follows:

for k,v in D2.items():
    try:
        D1[k] += v
    except KeyError:
        D1[k] = v