On 30/09/2021 18.11, Anil Anvesh wrote:
> I want to write a python calculator program that has different methods to
> add, subtract, multiply which takes 2 parameters. I need to have an execute
> method when passed with 3 parameters, should call respective method and
> perform the operation. How can I achieve that?
>
>
>
> class calc():
> def __init__(self,a,b):
> self.a=a
> self.b=b
>
> def ex(self,fun):
> self.fun=fun
> if fun=="add":
> self.add()
>
> def add(self):
> return self.a+self.b
> def sub(self):
> return self.a-self.b
> def mul(self):
> return self.a*self.b
> def div (self):
> return self.a/self.b
> def execu(
> obj1=calc()
> obj1.execu("add",1,,2)
>
This is a common course-assignment.
NB the code-examples below are incomplete. You may need to research
these techniques further, and thus learn how 'it' all fits-together
(I set 'homework' rather than doing it!)
There are several techniques which can be employed and/or combined here.
1 if-elif 'ladder'
2 dict[ionary] as select/case construct
3 functions as 'first-class objects'
The basic problem is to take a 'command' which is formatted as a
str[ing], and decide which of several options to choose:
1 if-elif is a simple and easy-to-read solution:
if command == "add":
do_this...
elif command == "sub":
do_that...
...
else:
# oops: "I'm afraid I can't do that, Dave"
# don't forget to add a 'catch-all' to handle user-error!
2 using a dict is shorter and avoids some of the 'boiler-plate'
repetition which causes many of us to rebel against using the above. We
use the command received from the user as a key into the dict.
3 a function and/or its name is as much data as the 'variable' "command"
or indeed the str-constant "add" - once it has been defined! Thus it is
possible to treat functions like anything else:
data_as_string = "my string"
# can be likened to:-
def my_function(): pass
data_as_function = my_function
Note that (like most else), the function must be defined before it can
be 'used'!
Returning to the stated-problem:
def add( etc ): ...
then using the if-elif 'ladder' above as a framework create a dict which
'links' the input command (as str) to the applicable function:
calculator = { "add": add,
"sub": sub,
# indeed we can become rather more 'creative'
"+" " add,
...
}
Thereafter, we can apply the dict to solve the problem:
calculator.get( command,
"Error message/advice, eg mentioning add, or + etc"
)
NB it has been left to you to perfect the technique so that the value(s)
to be calculated are properly communicated to the chosen function.
PS you may find the Python-Tutor Discussion List helpful
--
Regards,
=dn
--
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