Functional-programming-in-Python

Nowadays functional programming is becoming a new trend and people looking for Haskell and Scala as pure functional languages. But I think functional programming is not limited to these languages.

I want to share my findings that how can we achieve pure functional programming with Python so that one can use the power of functional programming who is already familiar with Python without jumping on Scala or Haskell. So let's dive in!

Let's Understand Higher Order Function (HOF)

HOF if Function which will accept the argument as function and return function as well.

NOTE : Use Debugger to Understand the flow of code.

print('\nHigher Order Function\n')
def Login(func,username,password):
  isValid = func(username, password)
  if isValid:
    return f'Welcome {username}'
  else:
    return 'Invalid username or password... ?'
  
def validate_user_data(temp_uname, temp_pass):
  if temp_uname.strip()=='Mike' and temp_pass.strip()=='mikeee128':
    return True
    
def get_user_details():
  uname = str(input('Enter your username:'))
  passwrd = str(input('Enter your password:'))

  return uname,passwrd

if __name__=='__main__':
  usrname, paswd = get_user_details()
  print(f'1.{Login(validate_user_data, usrname, paswd)}')

In above example I have created 3 function but if you Notice In “Login” Function I have passed the “validate_user_data” as an argument and used that function future in my code.

Currying

We can use higher-order functions to convert a function that takes multiple arguments into a chain of functions that each takes a single argument. More specifically, given a function f(x, y), we can define a function g such that g(x)(y) is equivalent to f(x, y). Here, g is a higher-order function that takes in a single argument x and returns another function that takes in a single argument y. This transformation is called currying.

‘’’ Example ‘’’

1st Example.

print('\n\nCurrying\n')

def get_1st_number(num_1):
  def get_2nd_number(num_2):
    return num_1+num_2

  return get_2nd_number

if __name__=='__main__':
  print(f'1. Addition of two Number: {get_1st_number(10)(20)}')

The above function is pure function because it does not depend upon any other variable besides its scope.

2nd Example

def pas_function(user_func):
  def get_x(x):
    def get_y(y):
      return user_func(x,y)
    return get_y
  return get_x

def mul_function(a,b):
  return a+b

pas_func = pas_function(mul_function)
print(f'2. Currying With user define or pre define function:{pas_func(2)(4)}\n')

In above example you can apply any function which applicable for two arguments such as “max”,”min”, “pow”. etc. You can also passs user define function ..in our case i have passed “mul_function”, you guys can yours Function but make sure that function will work on 2 parameter.

Higher Order Function With Currying

print('\nHigher order fucntion with Currying\n')


def Login(func,welcom_func):
    def get_username(uname):
        def get_password(pas):
            isValid = func(get_user_details,uname,pas)
            if isValid:
                return welcom_func(uname)
            else:
                return Invalid_user()
        return get_password
    return get_username

def check_valid_User(func_user_input,usernm,userpas):
    tempUname,tempPass = func_user_input()
    return ((tempUname.strip()==usernm) and (tempPass.strip()==userpas.strip()))

def welcome_user(uname):
    return f'Welcome {uname}'

def Invalid_user():
    return 'invalid username or password'

def get_user_details():
    tempName = str(input('Username:'))
    tempPass = str(input('Password:'))
    return str(tempName).strip(), str(tempPass).strip()

login = Login(check_valid_User,welcome_user)
print(login('Mike')('Mikeee'))

Final note

I hope this article helped you to get familiar with functional programming with Python. This is my first article on Medium so please do let me know what do you think about it in comment section below. Comment and criticism is always welcome!