A default parameter is a value provided in function declaration that is automatically assigned by the compiler if caller of the function doesn’t provide a value for the parameter with default value. Following is a simple Python example to demonstrate use of default parameters. We don’t have to write 3 Multiply functions, only one function works by using default values for 3rd and 4th parameters.
# A function with default arguments, it can be called with
# 2 arguments or 3 arguments or 4 arguments .
def Multiply( num1,num2,num3 = 5,num4 = 10 ) :
return num1 * num2 * num3 * num4
# Driver code
if __name__ == "__main__" :
print( Multiply( 2 , 3 ) )
print( Multiply( 2 , 3 , 4 ))
print( Multiply( 2 , 3 , 4 , 6))
Output:
300 240 144
Key Points:
- Default parameters are different from constant parameters as constant parameters can’t be changed whereas default parameters can be overwritten if required.
- Default parameters are overwritten when calling function provides values for them. For example, calling of function Multiply(2, 3, 4, 6) overwrites the value of num3 and num4 to 4 and 6 respectively.
- During calling of function, arguments from calling function to parameters of called function are copied from left to right. Therefore, Multiply(2, 3, 4) will assign 2, 3 and 4 to num1, num2 and num3. Therefore, default value is used for num4 only.