Question

I just want to know a easy way to extract all data with same key "Cat" from the dictionary into another array.

From the below dictionary..
All data with key "Cat: Book" should be in a separate array and key "Cat: pen" in another.
This dictionary is dynamic and more different "Cat" values can come in.

category= [{'Cat':'Book','Item':'LongBook','Qty':'25'}, 
           {'Cat':'Book','Item':'Diary','Qty':'20'}, 
           {'Cat':'Pen','Item':'BallPoint','Qty':'30'}]

Answer 1

It is quite difficult to understand what do you really need. Anyway try to take a look at the following code that uses defaultdict:

category= [{'Cat':'Book','Item':'LongBook','Qty':'25'}, 
           {'Cat':'Book','Item':'Diary','Qty':'20'}, 
           {'Cat':'Pen','Item':'BallPoint','Qty':'30'}]

from collections import defaultdict

output = defaultdict(list)

for row in category:
    output['Cat' + ':' + row['Cat']].append(row)

print output.values()

>>>[[{'Item': 'BallPoint', 'Qty': '30', 'Cat': 'Pen'}], [{'Item': 'LongBook', 'Qty': '25', 'Cat': 'Book'}, {'Item': 'Diary', 'Qty': '20', 'Cat': 'Book'}]]

Or better use groupby:

category= [{'Cat':'Book','Item':'LongBook','Qty':'25'}, 
           {'Cat':'Book','Item':'Diary','Qty':'20'}, 
           {'Cat':'Pen','Item':'BallPoint','Qty':'30'}]

from itertools import groupby

for key, vals in groupby(category, lambda x: x['Cat']):
    print key, list(vals)

>>>Book [{'Item': 'LongBook', 'Qty': '25', 'Cat': 'Book'}, {'Item': 'Diary', 'Qty': '20', 'Cat': 'Book'}]
>>>Pen [{'Item': 'BallPoint', 'Qty': '30', 'Cat': 'Pen'}]