Arguments types in Python Function

Python supports three type of formal argument / parameters.

1. Positional argument (Required)
2. Default argument
3. Keyword argument (named argument)

Positional argument (Required)

For example, function sum_of_three (a, b, c) calculating the sum of three variables. In this number of passed values must matched with number of received values.

Output is :

sum= 60

sum= 35

sum= 600

The argument must be provided for all parameters (Required) if I miss any there will be error. eg sum_of_three (x,y)  here third parameter is missing hence python shows error .

Another thing value of argument are matched with parameters (position) order wise.

For example 

Here in function intro(age, name)  , age is integer type and name is string type so we taken care about position  also while calling function. Look at the example where we call

• intro(a,s) # integer and string
• intro(s,a) # string and integer

Output is :

your name is Rahul and you are  18  years old

your name is 18  and you are  Rahul  years old (due to wrong position of arguments )

2) Default Parameters: –

What if we already know the value of certain parameters then eg same function sum_of_three (a, b, c) calculating the sum of three variables. In this number of passed values must matched with number of received values. If we call this as sum_of_three(x,y) with two parameters it will give us error because three parameters are must.

But what happens when we know the value of c in sum_of_three (a, b, c), then it is possible to call this with two parameters also sum_of_three(x,y) ..here third parameter is missing

  Look at the example.

In above example sum_of_three(x,y,z) and sum_of_three(x,y) both are worked

Output is :

sum= 60

sum= 31

Default parameters may be one, two or n but default parameter before required parameter is not allowed eg

sum_of_three(a, b=1 ,c)  gives error

if function having three parameters and two from them are default then they must before require parameter.

sum_of_three(a, b ,c=1)   # legal

sum_of_three(a, b=1,c=1)   # legal

sum_of_three(a, b=1,c)   # illegal

sum_of_three(a=1, b, c=1)   # illegal

sum_of_three(a=3, b=2,c=1)   # legal

In same way if we calculating simple interest in python and company mostly have interest rate 10% then we take rate as default parameter with value 10.0 and we call this function with three parameters as well as with two parameters also.

3) Keyword argument: – Default argument gives you flexibility to specify the default value for the parameter but still you cannot change the order, in short you remember the correct order of argument.

def interest(prin, time, rate=10.0):

    amt=(prin*time*rate)/100

    return amt

print(interest(20000,2,12.0))

print(interest(20000,12.0,2)) # here time is 12 years and rate is 2 %

so keywords arguments works here we can write any argument in any order providing name the argument. eg

 print (interest (20000, rate=12.0, time=2))

print (interest (rate=12.0, time=2, prin=20000))

this is the way for specifying names for the values is known as keyword arguments.