Python dict.fromkeys() Method

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.

♥️ Info: Are you AI curious but you still have to create real impactful projects? Join our official AI builder club on Skool (only $5): SHIP! - One Project Per Month

dict.fromkeys() Syntax

Method declaration:

dict.fromKeys(keys, optional_value)

Parameter Arguments:

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: {}}