Python

fromkeys() method in dictionary

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fromkeys() method in dictionary - Python

This method is used to create a dictionary from specified key and default value for all the keys.

It returns a new dictionary with specified key and values.

The time complexity of this method is O(n), where n is the number of keys specified in the input sequence. This is because the method needs to iterate over each key in the input sequence and set the corresponding default value.

The .fromkeys() method is convenient for creating dictionaries where you want to initialize multiple keys with the same default value. It is especially useful when you want to set default values for keys without having to iterate through them individually.

Syntax –

dict.fromkeys(keys, value)

Parameters –

keys → A sequence (e.g., a list, tuple, or string) containing the keys for the new dictionary.

value (optional) → The value to be set for all the keys in the new dictionary. If not provided, it defaults to None.

Return Value → returns a new dictionary with the specified keys and the specified default value.

Example 1-

				
					# Using fromkeys() to create a dictionary with default values
keys_list = ['a', 'b', 'c']
default_value = 0
new_dict = dict.fromkeys(keys_list, default_value)

print("New Dictionary:", new_dict)

# Output -
# New Dictionary: {'a': 0, 'b': 0, 'c': 0}

In the above example –

We use the .fromkeys() method to create a new dictionary (new_dict) with keys specified in the keys_list and a default value of 0.

The new dictionary is then printed, showing that each key from keys_list is present in the dictionary with the specified default value.

Example 2- Initializing with Numeric Keys

				
					# Using fromkeys() to create a dictionary with numeric keys
numeric_keys = range(1, 4)
default_value = 'default'
numeric_dict = dict.fromkeys(numeric_keys, default_value)

print("Numeric Dictionary:", numeric_dict)

# Output -
# Numeric Dictionary: {1: 'default', 2: 'default', 3: 'default'}

Example 3- Initializing with String Keys

				
					# Using fromkeys() to create a dictionary with string keys
string_keys = ['apple', 'banana', 'orange']
default_quantity = 0
fruits_dict = dict.fromkeys(string_keys, default_quantity)

print("Fruits Dictionary:", fruits_dict)

# Output -
# Fruits Dictionary: {'apple': 0, 'banana': 0, 'orange': 0}

Example 4- Initializing with Default Value as a List

				
					# Using fromkeys() to create a dictionary with default value as a list
keys_list = ['x', 'y', 'z']
default_list = []
list_dict = dict.fromkeys(keys_list, default_list)

# Modifying one of the lists
list_dict['x'].append(1)

print("List Dictionary:", list_dict)

# Output -
# List Dictionary: {'x': [1], 'y': [], 'z': []}

Example 5- Initializing with Different Default Values

				
					# Using fromkeys() to create a dictionary with different default values
keys = ['red', 'green', 'blue']
default_values = {'red': '#FF0000', 'green': '#00FF00', 'blue': '#0000FF'}
color_dict = dict.fromkeys(keys, default_values)

print("Color Dictionary:", color_dict)

# Output -
# Color Dictionary: {'red': {'red': '#FF0000', 'green': '#00FF00', 'blue': '#0000FF'},
#                   'green': {'red': '#FF0000', 'green': '#00FF00', 'blue': '#0000FF'},
#                  'blue': {'red': '#FF0000', 'green': '#00FF00', 'blue': '#0000FF'}}

Example 6-

				
					# Using fromkeys() to create a dictionary with default value as None
keys_list = ['a', 'b', 'c']
default_dict = dict.fromkeys(keys_list)

print("Default Dictionary:", default_dict)

# Output -
# Default Dictionary: {'a': None, 'b': None, 'c': None}

Python

fromkeys() method in dictionary

fromkeys() method in dictionary - Python

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