Page 250 - Computer Science V2.0 Class 11

9.2 User-defined Functions Revisited

Program 9.1 Write a function interest(principal,rate,time) that compute simple interest.
Let us reconsider the interest() function, developed to compute simple interest for the given principal amount,
rate of interest per cent per annum, and time in years (Program 9.1).
01 def interest(principal, rate, time):
02 '''
03 Objective: To determine simple interest
04 Input Parameters:
05 principal- numeric value denoting principal amount
06 rate - numeric value denoting rate of interest in % per annum
07 time - numeric values indicating time period in years
08 Return value: float-simple interest
09 '''
10 simpleInterest = (principal*rate*time)/100
11 return simpleInterest
9.2.1 Default Parameters

So far, we have learnt that a function call must have the same number of arguments as defined in the function
definition. Let us consider the function interest() again, but this time we imagine a scenario where the interest
rate is 4% and the interest is usually computed for one year. In such a scenario, it would make sense to initialise the
values of the formal parameters rate and time to 4 and 1, respectively, while defining the function interest().
The formal parameters (rate and time in case of interest()) whose values are initialised as part of the function
definition are called default parameters. The values assigned to the formal parameters are called the default values
of the parameters. To define the function interest()with the default parameters, we only need to modify the
function header (line 1) to specify the default values of the parameters as shown below:

01 def interest(principal, rate = 4, time = 1):
02 '''
03 Objective: To determine simple interest
04 Input Parameters:
05 principal- numeric value denoting principal amount
06 rate - numeric value denoting a rate of interest in % per annum
07 time - numeric values indicating a time period in years
08 Return value: float-simple interest
09 '''
10 simpleInterest = (principal*rate*time)/100
11 return simpleInterest
Now, to compute the simple interest for principal amount of Rs.55,000 for one year at 4% interest, we only need
to invoke the function interest() with the argument 55000 and leave the other two parameters unspecified as
shown below:
>>> interest(55000)
2200.0
Of course, a user may still specify the values of the default parameters. When a user specifies the values of the default
parameters, the default values are ignored. Suppose we wish to compute the simple interest for the principal amount
of Rs.55000 for one year with an interest rate of 5%.To carry out this computation, the following call to the function
interest()takes the default value 1 for the parameter time:

>>> interest(55000, 5)
2750.0
We have already seen above that a function, such as interest(), may have more than one default parameters.
The unspecified parameters in the trailing sequence take the default values. So, if a parameter takes a default value,
then all the other parameters to its right must also take default values.

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