Python Lambda/Anonymous Function
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In Python, a lambda function is a special type of function without the function name. For example,
lambda : print('Hello World')
Here, we have created a lambda function that prints 'Hello World'.
Before you learn about lambdas, make sure to know about Python Functions.
Python lambda Function Declaration
We use the lambda keyword instead of def to create a lambda function. Here’s the syntax to declare the lambda function:
lambda argument(s) : expression
Here,
argument(s)– any value passed to the lambda functionexpression– expression is executed and returned
Let’s see an example,
greet = lambda : print('Hello World')
Here, we have defined a lambda function and assigned it to the variable named greet.
To execute this lambda function, we need to call it. Here’s how we can call the lambda function
# call the lambda
greet()
The lambda function above simply prints the text 'Hello World'.
Note: This lambda function doesn’t have any arguments.
Example: Python lambda Function
# declare a lambda function
greet = lambda : print('Hello World')
# call lambda function
greet()
# Output: Hello World
In the above example, we have defined a lambda function and assigned it to the greet variable.
When we call the lambda function, the print() statement inside the lambda function is executed.
Python lambda Function with an Argument
Similar to normal functions, the lambda function can also accept arguments. For example,
# lambda that accepts one argument
greet_user = lambda name : print('Hey there,', name)
# lambda call
greet_user('Delilah')
# Output: Hey there, Delilah
In the above example, we have assigned a lambda function to the greet_user variable.
Here, name after the lambda keyword specifies that the lambda function accepts the argument named name.
Notice the call of lambda function,
greet_user('Delilah')
Here, we have passed a string value 'Delilah' to our lambda function.
And finally, the statement inside the lambda function is executed.
Frequently Asked Questions
The filter() function in Python takes in a function and an iterable (lists, tuples, and strings) as arguments.
The function is called with all the items in the list and a new list is returned which contains items for which the function evaluates to True.
Let’s see an example,
# Program to filter out only the even items from a list
my_list = [1, 5, 4, 6, 8, 11, 3, 12]
new_list = list(filter(lambda x: (x%2 == 0) , my_list))
print(new_list)
# Output: [4, 6, 8, 12]
Here, the filter() function returns only even numbers from a list.
The map() function in Python takes in a function and an iterable (lists, tuples, and strings) as arguments.
The function is called with all the items in the list and a new list is returned which contains items returned by that function for each item.
Let’s see an example,
# Program to double each item in a list using map()
my_list = [1, 5, 4, 6, 8, 11, 3, 12]
new_list = list(map(lambda x: x * 2 , my_list))
print(new_list)
# Output: [2, 10, 8, 12, 16, 22, 6, 24]
Here, the map() function doubles all the items in a list.
