Python | Clearing list as dictionary value

Last Updated : 29 Mar, 2019

Clearing a list is a common problem and solution to it has been discussed many times. But sometimes, we don’t have a native list but list is a value to dictionary key. Clearing it is not as easy as clearing an original list. Let’s discuss certain ways in which this can be done.

Method #1 : Using loop + clear()
This is the most generic method in which we can perform this particular function. We just run a loop till the last dictionary key and clear the key’s list value as they occur using clear function.

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# Python3 code to demonstrate
# clearing list as dict. value
# using loop + clear()
  
# initializing dict.
test_dict = {"Akash" : [1, 4, 3],
             "Nikhil" : [3, 4, 1],
             "Akshat" : [7, 8]}
  
# printing original dict
print("The original dict : " + str(test_dict))
  
# using loop + clear()
# clearing list as dict. value
for key in test_dict:
    test_dict[key].clear()
  
# print result
print("The dictionary after clearing value list : " + str(test_dict))

Output :

The original dict : {‘Nikhil’: [3, 4, 1], ‘Akshat’: [7, 8], ‘Akash’: [1, 4, 3]}
The dictionary after clearing value list : {‘Nikhil’: [], ‘Akshat’: [], ‘Akash’: []}

Method #2 : Using dictionary comprehension
We can reduce the lines of code and merge the above functionality using just the dictionary comprehension and clearing the list using the list re-initialization.

# Python3 code to demonstrate
# clearing list as dict. value
# using dictionary comprehension
  
# initializing dict.
test_dict = {"Akash" : [1, 4, 3],
             "Nikhil" : [3, 4, 1],
             "Akshat" : [7, 8]}
  
# printing original dict
print("The original dict : " + str(test_dict))
  
# using dictionary comprehension
# clearing list as dict. value
test_dict = {key : [] for key in test_dict}
  
# print result
print("The dictionary after clearing value list : " + str(test_dict))

Output :

The original dict : {‘Nikhil’: [3, 4, 1], ‘Akshat’: [7, 8], ‘Akash’: [1, 4, 3]}
The dictionary after clearing value list : {‘Nikhil’: [], ‘Akshat’: [], ‘Akash’: []}

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Python | Clearing list as dictionary value