Python – Initialize dictionary with custom value list

In python one usually comes across situations in which one has to use dictionary for storing the lists. But in those cases, one usually checks for first element and then creates a list corresponding to key when it comes. But its always wanted a method to initialize the dict. keys with a custom list. Let’s discuss certain ways to achieve this particular task.

Method #1 : Using Dictionary comprehension
This is most sought of method to do this initialization. In this method, we create the no. of keys we require and then initialize the customlist as we keep on creating the keys, so as to facilitate the append operation afterwards without an error.

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# Python3 code to demonstrate 
# Custom list dictionary initialization
# using dictionary comprehension
  
# initialize custom list 
cus_list = [4, 6]
  
# using dictionary comprehension to construct
new_dict = {new_list: cus_list for new_list in range(4)}
      
# printing result
print ("New dictionary with custom list as keys : " + str(new_dict))

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Output :

New dictionary with custom list as keys : {0: [4, 6], 1: [4, 6], 2: [4, 6], 3: [4, 6]}

 

Method #2 : Using fromkeys()
fromkeys() can be used to perform this by specifying the additional custom list as argument and the range of elements which need to be the key of dictionary being made.

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# Python3 code to demonstrate 
# Custom list dictionary initialization
# using fromkeys()
  
# initialization custom list 
cus_list = [4, 6]
  
# using fromkeys() to construct
new_dict = dict.fromkeys(range(4), cus_list)
      
# printing result
print ("New dictionary with custom list as keys : " + str(new_dict))

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Output :

New dictionary with custom list as keys : {0: [4, 6], 1: [4, 6], 2: [4, 6], 3: [4, 6]}
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