#PYTHON(DAY18)recurssion,lambda,filter and map functions

 

#PYTHON(DAY18)

recurssion function

• recurssion func is a function which calls up on itself
• Note: this kind of fun needs a base case to stop, if not the execution stack will reaches max depth and exhaust the memory( if you are using jupyter notebook the kernel will be dead)

recurssion function

# factorial with using recurssion
def fact(n):
    fact = 1
    for i in range(1,n+1):
        fact = fact*i
        n-=1
    return fact

fact(4)

And the output is:

24

lambda functions

• these functions are called as anonymous functions
• these are defined in a single line
• syntax for lambda functions:
• ‘lambda’ var_name: <’statement/s using these var/s’>
• these functions by default will return a value, no need to write a return statement
• there is no cap on no of vars one can use to define a lambda function

lambda function

# normal func
def powAB(a,b):
    return a**b
powAB(4,5)

And the output is:

1024

filter()

• filter function is used to filter the elements based on user’s logic
• this user’s logic is written as function, which gives a boolean output, True when it meets the user’s logic, or else it will return False
• filter function will return an iterator of cls=ass filter, we can typecast this to a list
• filter function accepts 2 parameters 1) function 2) iterator/container
• syntax of filter function:
• filter(func,container/iterator)

filter function

nums = [i for i in range(1,51)]
even = filter(lambda num: num%2 == 0,nums)
odd = filter(lambda num: num%2 !=0, nums)
print(type(even),type(odd))
even,odd = list(even),list(odd)
print(type(even),type(odd))
print(even,odd,sep = '\n')

And the output is:

<class 'filter'> <class 'filter'>
<class 'list'> <class 'list'>
[2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50]
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49]

map

• we use ‘map’ function to apply our function on each element of an iterator
• syntax of ‘map’ function:
• map(func,iterator)
• output of map function is a map object, we need to type cast it to a list or other data types to see the output

map function

nums = [ele for ele in range(1,11)]
cube_nums = map(lambda x : x**3, nums)
print(cube_nums, type(cube_nums), sep = '\n')
cube_nums = list(cube_nums)
print(cube_nums, type(cube_nums),sep = '\n')

And the output is:

<map object at 0x00000230D2B6B700>
<class 'map'>
[1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
<class 'list'>