The fromkeys() function in python helps to create a new dictionary using the given sequence with given values.
dictionary.fromkeys(sequence[, value]) #where sequence may be a integers, string etc
Takes two parameters. In case if we create a dictionary from a mutable(value can be changed) object list and later the mutable object is changed then it will reflect each of the elements in the sequence. This is because each element is pointed to the same object in the memory. To avoid this problem, dictionary comprehension is used.
| Parameter | Description | Required / Optional |
|---|---|---|
| sequence | sequence of elements which is to be used as keys for the new dictionary | Required |
| value | value which is set to each each element of the dictionary.Default value is None | Optional |
If the value argument is given, each element of the newly created dictionary is assigned with the provided value.
| Input | Return Value |
|---|---|
| If parameters | new dictionary |
# vowels keys
keylist = {'a', 'e', 'i', 'o', 'u' }
vowelslist = dict.fromkeys(keylist)
print(vowelslist)
Output:
{'a': None, 'u': None, 'o': None, 'e': None, 'i': None}
# vowels keys
keylist = {'a', 'e', 'i', 'o', 'u' }
value = 'vowel'
vowelslist = dict.fromkeys(keylist, value)
print(vowelslist)
Output:
{'a': 'vowel', 'u': 'vowel', 'o': 'vowel', 'e': 'vowel', 'i': 'vowel'}
# vowels keys
keylist = {'a', 'e', 'i', 'o', 'u' }
value = [4]
vowelslist = dict.fromkeys(keylist, value)
print(vowelslist)
# updating the value
value.append(5)
print(vowelslist)
Output:
{'a': [4], 'u': [4], 'o': [4], 'e': [4], 'i': [4]}
{'a': [4, 5], 'u': [4, 5], 'o': [4, 5], 'e': [4, 5], 'i': [4, 5]}
