Python Lambda Functions


Why Use Lambda Functions?

The power of lambda is better shown when you use them as an anonymous function inside another function.

Say you have a function definition that takes one argument, and that argument will be multiplied with an unknown number:

def myfunc(n):
      return lambda a : a * n

Use that function definition to make a function that always doubles the number you send in:

Example:1
Python program to double the value.
Sol:

#without user input
def myfunc(n):
  return lambda a : a * n

doub = myfunc(2)

print(doub(11))

Output:

22
>>>

Example:2
Python program to double the value (using user input).
Sol:

#without user input
def myfunc(n):
  return lambda a : a * n

doub = myfunc(2)
z=int(input("Enter the value to double "))
print(doub(z))

Output:

Enter the value to double 5
10
>>>

Example:3
Python program to print the square of value(without user input).
Sol:

#without user input
def myfunc(n):
  return lambda a : a ** n 

square = myfunc(2)
print(square(5))

Output:

25
>>>

Example:4
Python program to print square of a value(Using user input).
Sol:

#Using user input
def myfunc(n):
  return lambda a : a ** n 

square = myfunc(2)
z=int(input("Enter the value to square "))
print(square(z))

Output:

Enter the value to square 6
36
>>>

Example:5
Python program to print the cube of value(without user input).
Sol:

#without user input
def myfunc(n):
  return lambda a : a ** n 

cube = myfunc(3)
print(cube(5))

Output:

125
>>>

Example:6
Python program to print cube of a value(Using user input).
Sol:

#Using user input
def myfunc(n):
  return lambda a : a ** n 

cube = myfunc(3)
z=int(input("Enter the value to cube "))
print(cube(z))

Output:

Enter the value to cube 5
125
>>>


Important Use of Lambda Function in python

Use of Lambda Function in python

We use lambda functions when we require a nameless function for a short period of time.

In Python, we generally use it as an argument to a higher-order function (a function that takes in other functions as arguments). Lambda functions are used along with built-in functions like filter(), map() etc.

Example: use with filter()

The filter() function in Python takes in a function and a list 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.

Here is an example use of filter() function to filter out only even numbers from a list.

Example:1
# Program to filter out only the even items from a list
Sol:

n = [1, 5, 4, 6, 8, 11, 3, 12]

n1 = list(filter(lambda x: (x%2 == 0) , n))

print(n1)

Output:

[4, 6, 8, 12]
>>>

Example:2
python to create a list of elements further display all even elements present in the list.
Sol:

n=[]
while True:
    a=int(input("Enter number to add in list "))
    n.append(a)
    ch=input("Like to add another element ")
    if(ch=='y' or ch=='Y'):
        continue
    else:
        break

print("Full list is ")
print(n)
print("list of even number in the list ")

n1 = list(filter(lambda x: (x%2 == 0) , n))

print(n1)

Output:

Enter number to add in list 25
Like to add another element y
Enter number to add in list 95
Like to add another element y
Enter number to add in list 36
Like to add another element y
Enter number to add in list 45
Like to add another element y
Enter number to add in list 22
Like to add another element y
Enter number to add in list 78
Like to add another element y
Enter number to add in list 81
Like to add another element y
Enter number to add in list 45
Like to add another element n
Full list is
[25, 95, 36, 45, 22, 78, 81, 45]
list of even number in the list
[36, 22, 78]
>>>

Example:3
# Program to filter out only the odd items from a list
Sol:

n = [11, 55, 24, 61, 8, 211, 3, 112,15]

n1 = list(filter(lambda x: (x%2 == 1) , n))

#Function call
print(n1)

Output:

[11, 55, 61, 211, 3, 15]
>>>

Example:4
python to create a list of elements further display all odd elements present in the list.
Sol:

n=[]
while True:
    a=int(input("Enter number to add in list "))
    n.append(a)
    ch=input("Like to add another element ")
    if(ch=='y' or ch=='Y'):
        continue
    else:
        break

print("Full list is ")
print(n)
print("list of odd number in the list ")

n1 = list(filter(lambda x: (x%2 == 1) , n))

print(n1)

Output:

Enter number to add in list 5
Like to add another element y
Enter number to add in list 25
Like to add another element y
Enter number to add in list 32
Like to add another element y
Enter number to add in list 4
Like to add another element y
Enter number to add in list 21
Like to add another element y
Enter number to add in list 95
Like to add another element n
Full list is
[5, 25, 32, 4, 21, 95]
list of odd number in the list
[5, 25, 21, 95]
>>>

Example:5
python to create a list of elements further display all multiples of 5 present in the list.
Sol:

n=[]
while True:
    a=int(input("Enter number to add in list "))
    n.append(a)
    ch=input("Like to add another element ")
    if(ch=='y' or ch=='Y'):
        continue
    else:
        break

print("Full list is ")
print(n)
print("list of multiple of 5 in the list ")

n1 = list(filter(lambda x: (x%5 == 0) , n))

print(n1)

Output:

Enter number to add in list 25
Like to add another element y
Enter number to add in list 36
Like to add another element y
Enter number to add in list 45
Like to add another element y
Enter number to add in list 44
Like to add another element y
Enter number to add in list 95
Like to add another element y
Enter number to add in list 78
Like to add another element y
Enter number to add in list 75
Like to add another element y
Enter number to add in list 41
Like to add another element y
Enter number to add in list 24
Like to add another element n
Full list is
[25, 36, 45, 44, 95, 78, 75, 41, 24]
list of multiple of 5 in the list
[25, 45, 95, 75]
>>>

Example: use with map()

The map() function in Python takes in a function and a list.
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.

Example:1
# python Program to double each item in a list using map()
Sol:

n = [1,3,2,6,5,8,7,3,10]

n1 = list(map(lambda x: x * 2 , n))

print("List with elements")
print(n)
print("List with double of elements ")
print(n1)

Output:

List with elements
[1, 3, 2, 6, 5, 8, 7, 3, 10]
List with double of elements
[2, 6, 4, 12, 10, 16, 14, 6, 20]
>>>

Example:2
# Python Program to square each item in a list using map()
Sol:

n = [1,3,2,6,5,8,7,3,10]

n1 = list(map(lambda x: x ** 2 , n))

print("List with elements")
print(n)
print("List with square of elements ")
print(n1)

Output:

List with elements
[1, 3, 2, 6, 5, 8, 7, 3, 10]
List with square of elements
[1, 9, 4, 36, 25, 64, 49, 9, 100]
>>>

Example:3
# Python Program to calculate cube each item in a list using map()
Sol:

n = [1,3,2,6,5,8,7,3,10]

n1 = list(map(lambda x: x ** 3 , n))

print("List with elements")
print(n)
print("List with cube of elements ")
print(n1)

Output:

List with elements
[1, 3, 2, 6, 5, 8, 7, 3, 10]
List with cube of elements
[1, 27, 8, 216, 125, 512, 343, 27, 1000]
>>>

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