Combine similar functions into one (Python)

Question

I have the following two very similar functions:

# Get value as int
def get_int(message):
    while True:
        try:
            number = int(input(message))
            return number
        except ValueError:
            print("Invalid input. Try again.")

# Get value as fraction
def get_fraction(message):
    while True:
        try:
            number = Fraction(input(message))
            return number
        except ValueError:
            print("Invalid input. Try again.")

Now I am wondering if that can be done in a simpler way, by combining these two functions into one. This is my first attemt:

# Get value as specific data type
def get_value(message, data_type):
    while True:
        try:
            number = None
            match data_type:
                case "int":
                    number = int(input(message))
                case "fraction":
                    number = Fraction(input(message))
            return number
        except ValueError:
            print("Invalid input. Try again.")

So now I'm passing the data type as an argument. But I am sure there is a simpler way without using a case distinction. Can I pass somehow the real data datype to the function and use this directly in the code?

@Tomerikoo It's probably from here: docs.python.org/3/library/fractions.html — jjramsey
– jjramsey, Commented Nov 9, 2021 at 16:36
FYI, you're on the verge of rediscovering the Strategy Pattern. — jjramsey
– jjramsey, Commented Nov 9, 2021 at 16:37

Marat · Accepted Answer · 2021-11-18 17:48:47Z

3

Great news: types are first-order citizens in Python. You can do something like this:

def get_value(message, data_type):
    while True:
        try:
            return data_type(input(message))
        except ValueError:
            print("Invalid input. Try again.")

And then call it like this:

get_value("Input an integer:", int)
# or,
get_value("Input a fraction:", Fraction)

edited Nov 18, 2021 at 17:48

answered Nov 9, 2021 at 16:33

Marat

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1 Comment

escape99 Over a year ago

Wow ok! Didn't think it could be that easy. Thanks!

Prasanna · Accepted Answer · 2021-11-09 16:32:31Z

Python has decorators for this same task.

# the decorator
def calculate(function):
   
   # the wrapper function
   def wrapper(message):
        while True:
        try:
            number = function(message)
            return number
        except ValueError:
            print("Invalid input. Try again.")

   return wrapper

Now you just use this in your functions:

# Get value as int
@calculate
def get_int(message):
   return int(input(message))


# Get value as fraction
@calculate
def get_fraction(message):
    return Fraction(input(message))

What's happening here is you are defining a function, that takes a function as input. In this case, it is the calculate function. It is taking in the get_int and get_fraction function as inputs.

So when you call the function get_init, it is actually calling calculate(get_init) which is also a function that takes message as input.

Random Davis · Accepted Answer · 2021-11-09 16:33:39Z

1

Can I pass somehow the real data datype to the function and use this directly in the code?

There's nothing stopping you from passing the actual data type rather than a string:

# Get value as specific data type
def get_value(message, data_type):
    while True:
        try:
            number = data_type(input(message))
            return number
        except ValueError:
            print("Invalid input. Try again.")

Test:

print(get_value('Enter a fraction: ', Fraction))

Output:

Enter a fraction: 1/3
1/3

answered Nov 9, 2021 at 16:33

Random Davis

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1 Comment

escape99 Over a year ago

Thanks! Coming from other languages like Java it is amazing how intuitive python is.

Barmar · Accepted Answer · 2021-11-09 16:35:07Z

1

You can pass the conversion function itself, rather than a string.

# Get value as specific data type
def get_value(message, converter):
    while True:
        try:
            number = converter(input(message))
            return number
        except ValueError:
            print("Invalid input. Try again.")

def get_int(message):
    return get_value(message, int)

def get_fraction(message):
    return get_value(message, Fraction)

answered Nov 9, 2021 at 16:35

Barmar

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Comments

Tomerikoo · Accepted Answer · 2021-11-09 19:46:16Z

1

You can pass references to functions just like any other variable. Therefore:

def get_value(message, data_type):
  while True:
    try:
      return data_type(input(message))
    except ValueError:
      print('Invalid input. Try again')

x = get_value('Enter a fraction', Fraction)
y = get_value('Enter an integer', int)

edited Nov 9, 2021 at 19:46

Tomerikoo

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answered Nov 9, 2021 at 16:34

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