如何在Python dict的值前附加键？

Question

I have a dict

x = {'[a]':'(1234)', '[b]':'(2345)', '[c]':'(xyzad)'}

Now I want to append the key before values, so my expected output is:

{'[a]': '[a](1234)', '[b]': '[b](2345)', '[c]': '[c](xyzad)'}

I can do it using for loop like below:

for k,v in x.items():
    x.update({k:k+v})

I am looking for efficent way of doing this or I should stick to my current approach?

Answer 1

Your approach seems fine. You could also use a dictionary comprehension, for a more concise solution:

x = {'[a]':'(1234)', '[b]':'(2345)', '[c]':'(xyzad)'}

{k: k+v for k,v in x.items()}
# {'[a]': '[a](1234)', '[b]': '[b](2345)', '[c]': '[c](xyzad)'}

Answer 2

Another way:

x = {'[a]':'(1234)', '[b]':'(2345)', '[c]':'(xyzad)'}
dict(((key, key + x[key]) for key in x))
>>>{'[a]': '[a](1234)', '[b]': '[b](2345)', '[c]': '[c](xyzad)'}

Answer 3

For smaller size dictionaries, the dictionary comprehension solution by @yatu is the best.

Since you mentioned that the data set is large & you would like to avoid for loop, pandas would be the recommended solution.

1. Create pandas dataframe from dict 'x'
2. Transform the dataframe & write to a new dictionary

Code:

# Read dictionary to a dataframe
df = pd.DataFrame(list(x.items()), columns=['Key', 'Value'])

Out[317]: 
   Key    Value
0  [a]   (1234)
1  [b]   (2345)
2  [c]  (xyzad)

# Since the transformation is just concatenating both key and value, this can be done while writing to the new dictionary in a single step.
y = dict(zip(df.Key, df.Key+df.Value))

Out[324]: {'[a]': '[a](1234)', '[b]': '[b](2345)', '[c]': '[c](xyzad)'}

This would be much faster for large data sets but I'm not sure how to compare the timings.