Python: Lambda expressions

Lambda expressions are used to create anonymous functions. Using keyword ‘lambda’ we can create lambda expressions.

Syntax

lambda_expr        ::=  "lambda" [parameter_list]: expression

lambda_expr_nocond ::=  "lambda" [parameter_list]: expression_nocond

test.py

def square(x):
 return x*x

squareLambda = lambda x: x*x

print(square(10))
print(squareLambda(10))

As you see above code, both square, squareLambda doing exactly same operation, but defined in two ways. ‘square’ is defined using the keyword ‘def’, ‘squareLambda’ is defined using the keyword ‘lambda’.

As you see the lambda definition, it don’t return any value like function. Lambda contains an expression, which is returned as result to the caller.

test.py

def increment(n):
 return lambda x : x + n
 
incrementBy2 = increment(2)
incrementBy4 = increment(4)

incBy2 = lambda x : x + 2
incBy4 = lambda x : x + 4

print(incrementBy2(100))
print(incrementBy4(100))
print(incBy2(100))
print(incBy4(100))

$ python3 test.py

102

104

102

104

In the above code function ‘increment’ creates anonymous functions on the fly and return them.

incrementBy2 = increment(2) is same as incrementBy2 = lambda x : x + 2.

Another example to calculate sum of two numbers using lambda expressions.

test.py

sum = lambda x, y : x+y

print(sum(10, 20))
print(sum(1034, 2230))
print(sum(10342, 32450))

$ python3 test.py

30

3264

42792

Referred Articles

http://www.secnetix.de/olli/Python/lambda_functions.hawk

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