Python dict.fromkeys() Method

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The method dict.fromkeys() is a very useful method for creating new dictionaries from a given iterable of keys.

Definition: dict.fromkeys() is a method that inputs keys and maybe an optional value, and outputs a dictionary with the specified keys, that are mapped either to optionally specified values or to the default None value.

dict.fromkeys() Syntax

Method declaration:

dict.fromKeys(keys, optional_value)

Parameter Arguments:

keysrequired inputIterable input specifying the keys of the newly made dictionary
optional_valueoptional inputSpecified value assigned to every key in the dictionary, the default optional value is None.

Examples of dict.fromkeys() Method

Next, we’re going to examine three examples of the dict.fromkeys() method.

Example 1

The following is an example of an ordered integers dictionary, with and without an optional value.

# Initializing a number sequence:
sequence = {1, 2, 3, 4, 5}


# Use the dict.fromKeys() method to convert the sequence to a dictionary:
# Initializing with default None value:
result_dict = dict.fromkeys(sequence)
print('newly made dictionary with default None values: ', result_dict)


# Initializing another dictionary, with an optional value, 1 in this case:
result_dict2 = dict.fromkeys(sequence, 1)
print('2nd dictionary with 1 as the specified value: ', result_dict2)

This is the output of the previous code snippet:

newly made dictionary with default None values:  {1: None, 2: None, 3: None, 4: None, 5: None}
2nd dictionary with 1 as the specified value:  {1: 1, 2: 1, 3: 1, 4: 1, 5: 1}

Example 2

The following is an example of adding a specified default value:

a = ('key_1', 'key_2', 'key_3')
b = 7


default_dict = dict.fromkeys(a, b)
print(default_dict)
# {'key_1': 7, 'key_2': 7, 'key_3': 7}

Example 3

The following is an example of setting an empty dictionary {} as the default value to the dict.fromKeys() method:

new_dict = dict.fromkeys(range(5), {})
print('a new dictionary with empty dictionaries as values: ', new_dict)
# a new dictionary with empty dictionaries as values:  {0: {}, 1: {}, 2: {}, 3: {}, 4: {}}