What is a lambda expression?

Practicing Coding Interview Questions in Python

Kirill Smirnov

Data Science Consultant, Altran

Definition

lambda expression/function - is a short function having the following syntax:

lambda arg1, arg2, ...: expression(arg1, arg2, ...)
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Definition

lambda expression/function - is a short function having the following syntax:

lambda
Practicing Coding Interview Questions in Python

Definition

lambda expression/function - is a short function having the following syntax:

lambda arg1, arg2, ...:
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Definition

lambda expression/function - is a short function having the following syntax:

lambda arg1, arg2, ...: expression(arg1, arg2, ...)

lambda x: x**2

squared = lambda x: x**2

squared(4)

16

4 $\rightarrow$ x $\rightarrow$ x**2 $\rightarrow$ 16

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Definition

lambda expression/function - is a short function having the following syntax:

lambda arg1, arg2, ...: expression(arg1, arg2, ...)

power = lambda x, y: x**y

power(2, 3)

8

2, 3 $\rightarrow$ x, y $\rightarrow$ x**y $\rightarrow$ 8

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Missing argument

power = lambda x, y: x**y

 

power(2)

TypeError
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Comparison to normal function definition

squared_lambda = lambda x: x**2

def squared_normal(x):
    return x**2
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Comparison to normal function definition

                 lambda

def
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Comparison to normal function definition

squared_lambda = lambda

def squared_normal
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Comparison to normal function definition

squared_lambda = lambda x:

def squared_normal(x):
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Comparison to normal function definition

squared_lambda = lambda x: x**2

def squared_normal(x):
    return x**2

squared_lambda(3)

9

squared_normal(3)

9
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Passing lambda function as an argument

def function_with_callback(num, callback_function):
    return callback_function(num)

callback_function(arg) - a function with one argument

def squared_normal(x):
    return x**2

function_with_callback(2, squared_normal)

4
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Passing lambda function as an argument

def function_with_callback(num, callback_function):
    return callback_function(num)

callback_function(arg) - a function with one argument

--> def squared_normal(x): <--
-->    return x**2         <--

--> function_with_callback(2, squared_normal) <--

4
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Passing lambda function as an argument

def function_with_callback(num, callback_function):
    return callback_function(num)

callback_function(arg) - a function with one argument

function_with_callback(2, lambda x: x**2)

4
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Definition

lambda expression/function - is a short function having the following syntax:

lambda arg1, arg2, ...: expression(arg1, arg2, ...)
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Definition

lambda expression/function - is a short (anonymous) function having the following syntax:

lambda arg1, arg2, ...: expression(arg1, arg2, ...)

squared = lambda x: x**2
squared(3)

9
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Definition

lambda expression/function - is a short (anonymous) function having the following syntax:

lambda arg1, arg2, ...: expression(arg1, arg2, ...)

(lambda x: x**2)(3)

9
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Ternary operator

def odd_or_even(num):
    if num % 2 == 0:
        return 'even'
    else:
        return 'odd'

odd_or_even(3)

'odd'

odd_or_even(6)

'even'
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Ternary operator

def odd_or_even(num):
    return 'even' if num % 2 == 0 else 'odd'

odd_or_even(3)

'odd'

odd_or_even(6)

'even'
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Ternary operator

odd_or_even = lambda num: 'even' if num % 2 == 0 else 'odd'

odd_or_even(3)

'odd'

odd_or_even(6)

'even'
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Practical use

Use lambda expressions when it is really necessary!

  • within function bodies to perform a small task
  • as callbacks
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Let's practice!

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