在python中，结合2个字典的值

Question

I'm new to Python, and I have two questions regarding dictionary in python.

1. I have dict1 (where the values is already a list ), then I have dict2 with the same keys as dict1 , I want to add the new value to the list of values in dict1 . How can I write it? Can you show it with an example?

    dict1 = {'uid': ['u1'], 'sid': ['s1'], 'os': ['os1']} dict2 = {'uid': ['u2'], 'sid': ['s2'], 'os': ['os2']} 

   Expected output:

    dict1 = {'uid': ['u1', 'u2'], 'sid': ['s1', 's2'], 'os': ['os1', 'os2']} 

---

2. I will be process a lot of lines in a text file, with each line creating a new dictionary. Here is the idea of my code:

    count = 0 for line in f: if count == 0: dict1 = parse_qs(line) count = count+1 else: dict2 = parse_qs(line) #combine dict1 with dict 2, and assign the new dict to dict1 

Is there a better way that uses less memory or runs faster (still using dictionary)?

Thank you in advance for your help!

Answer 1

Since you're apparently not allowed to rewrite you parser, you can do:

for k in dict1:
    dict1[k].extend(dict2.get(k, []))

You can drop the .get and use direct subscription if the keys from both dicts are always matching.

for k in dict1:
    dict1[k].extend(dict2[k])

Otherwise, you can create one defaultdict(list) and let your parser append values to that.

Answer 2

You can do like this,

for key in dict1.keys():
     if dict2.has_key(key):
         dict1[key].extend(dict2[key])

if you are using python3 you can use key in dict2 instead of dict2.has_key(key) .

Result

{'os': ['os1', 'os2'], 'sid': ['s1', 's2'], 'uid': ['u1', 'u2']}

Answer 3

If you don't want the two dictionaries anymore then you can do this:

def merge_dict(dict1, dict2):
    for k in dict1:
        try:
            dict1[k].extend(dict2[k])
        except KeyError:
            pass
    return dict1

Else if you want to preserve them both for future use, try this

def merge_dict(dict1, dict2):
    new_dict = {}
    keys = dict1.keys() + dict2.keys()
    for k in keys:
        try:
            new_dict[k] = dict1[k]
        except KeyError:
            new_dict[k] = dict2[k]
            continue
        try:
            new_dict[k]+= dict2[k]
        except KeyError:
            pass
    return dict1

Answer 4

this may be helpful to you.

from itertools import chain
from collections import defaultdict

# ------ for dict1 -------#

u1 = [1,2,3]
s1 = ['a','b','c']
x1 = [10,100,1000]

# ------ for dict2 -------#

u2 = [4,5,6]
s2 = ['d','e','f']
x2 = ['aa','bb','cc']

dict1 = {1:u1,2:s1,3:x1}
dict2 = {1:u2,2:s2,3:x2}

dict3 = defaultdict(list)
for a, b in chain(dict1.items(), dict2.items()):
     dict3[a].append(b)

#for a, b in dict3.items():
#    print(a, b)

print dict3