Python | Iterate through value lists dictionary

Last Updated : 26 Jul, 2019

While working with dictionary, we can have a case in which we need to iterate through the lists, which are in the keys of dictionaries. This kind of problem can occur in web development domain. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using list comprehension
List comprehension can be used to perform this particular task. It is just the shorthand to the conventional nested loops. we iterate for each key’s list and store the result.

# Python3 code to demonstrate working of
# Iterating through value lists dictionary
# Using list comprehension
  
# Initialize dictionary
test_dict = {'gfg' : [1, 2], 'is' : [4, 5], 'best' : [7, 8]}
  
# printing original dictionary
print("The original dictionary : " +  str(test_dict))
  
# Using list comprehension
# Iterating through value lists dictionary
res = [[i for i in test_dict[x]] for x in test_dict.keys()]
      
# printing result 
print("The list values of keys are : " + str(res))

Output :

The original dictionary : {‘best’: [7, 8], ‘is’: [4, 5], ‘gfg’: [1, 2]}
The list values of keys are : [[7, 8], [4, 5], [1, 2]]

Method #2 : Using from_iterable() + product() + items()
The combination of above functions can be used to perform this particular task. The from_iterable() can be used to reduce inner loop and items function is used to extract key value pairs in the dictionary.

# Python3 code to demonstrate working of
# Iterating through value lists dictionary
# Using from_iterable() + product() + items()
import itertools
  
# Initialize dictionary
test_dict = {'gfg' : [1, 2], 'is' : [4, 5], 'best' : [7, 8]}
  
# printing original dictionary
print("The original dictionary : " +  str(test_dict))
  
# Iterating through value lists dictionary
# Using from_iterable() + product() + items()
res = []
for key, value in (
        itertools.chain.from_iterable(
            [itertools.product((k, ), v) for k, v in test_dict.items()])):
                res.append(value)
      
# printing result 
print("The list values of keys are : " + str(res))

Output :

The original dictionary : {‘best’: [7, 8], ‘is’: [4, 5], ‘gfg’: [1, 2]}
The list values of keys are : [7, 8, 1, 2, 4, 5]

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