CODEWITHSUNDEEP
pythonpython-3.xparameters
clovis
clovis

Reputation: 335

Parameter Errors

So I've defined a function called change(a,d) that computes the change of amount a given denominations d. I've also got some parameters: a must be of type int, d must be of type list of int, and the elements of d must be in ascending order, otherwise ChangeParameterError is raised. My code is as follows:

class ChangeRemainderError(Exception):
   pass

class ChangeParameterError(Exception):
   pass

def change(a, d):
    if type(a) != int:
      raise ChangeParameterError
    if type(d) != type(list):
      raise ChangeParameterError
    if type(d) != d.sort():
      raise ChangeParameterError

   i, r, c = len(d)-1, a, len(d)*[0]
   while i >= 0:
     c[i], r = divmod(r, d[i])
     i = i-1
   return c
def printChange(a, d):
    try:
        print(change(a, d))
    except ChangeParameterError:
        print('needs an integer amount and a non-empty list \
of denominations in ascending order')
    except ChangeRemainderError:
        print('no exact change possible')
    except:
        print('unexpected error')

and as it stands it's throw ChangeParameterError for tests it shouldn't be doing so. For example: change(3, [3, 7]) == [1, 0]

returns the ChangeParameterError even though a is an int and d is a list in ascending order. And the error message isn't really helpful. The error message is as follows:

<ipython-input-39-62477b9defff> in change(a, d)
     19         raise ChangeParameterError
     20     if type(d) != type(list):
---> 21         raise ChangeParameterError
     22     if type(d) != d.sort():
     23         raise ChangeParameterError

ChangeParameterError:

Any help is appreciated, thanks!

Upvotes: 0

Views: 64

Answers (1)

Jonathon Reinhart
Jonathon Reinhart

Reputation: 137418

You've got two logic errors that I can see. Try this instead:

def change(a, d):
    if type(a) != int:
      raise ChangeParameterError
    if type(d) != list:  # 1
      raise ChangeParameterError
    if d != sorted(d):  # 2
      raise ChangeParameterError

First, type(list) is going to return the type <type>.

Second, you included type(d) in your third check where it doesn't make sense. Also, d.sort() doesn't return anything; it sorts the list in place.

Also, it's better to use isinstance rather than checking the return value of type.

Upvotes: 1

Related Questions