[Tutor] Help with a funcion

[Cameron Simpson]

On 30Dec2019 13:09, Laura Schramm <laura.schramm92 at gmail.com> wrote:
>I was hoping you could help me out creating a function.

We can, but we won't actually write it for you. We will offer 
suggestions, but it works is best when you come with code you've written 
which doesn't work and explain what it currently does and what you 
actually want it to do.

Anyway, discussion and suggestions below:

>My professor has requested that I create a function that simulates m throws
>of a dice with n sides. The function should return a list of tuples with
>(value_side, percentage) for every side. The percentages should be
>expressed as a chain of text with a decimal and "%".
>
>For example: For 1000 throws of a dice with 4 sides the answer should look
>like
>[(1, 25.3%), (2, 25.8%), (3, 25.0%), (4, 24.5%)]

This looks much like the output of Python's repr() function, except that 
the percentages will be strings, so:

    [(1, '25.3%'), (2, '25.8%'), (3, '25.0%'), (4, '24.5%')]

For example, you can check the result of your programme like this:

   result = throws_of_dice(4, 100)
   print(repr(result))

which woould print a line like the above.

Python's interacive prompt doesthe second line for you if you're working 
that way:

    >>> throws_of_dice(4, 100)
    [(1, '25.3%'), (2, '25.8%'), (3, '25.0%'), (4, '24.5%')]
    >>>

(Note, no assignment to "result" there; that would omit the output.)

>I am given the prompt
>def throws_of_dice(n_sides, n_throws)

This is the start of your function definition. It will look more like 
this when written:

    def throws_of_dice(n_sides, n_throws):
        ... throw some dice many times, count the results ...
        return the list ofresults

You need to do a few things in your function:

- write a short "for" loop which runs n_throws times (see the range() 
  function for an easy way to do this)

      https://docs.python.org/3/reference/compound_stmts.html#the-for-statement

  There's even an example for-loop in the above using range().

- write a little line of code to simulate a throw, by computing a random 
  value from 1 to n_sides; see the "random" module, which has various 
  functions including one to compute a random value like that

      https://docs.python.org/3/library/random.html#module-random

- keep an association of the count of times each side shows up; the 
  simplest is a dict keyed on the "side" (a number from 1 to n_sides), 
  which you could prefill with 0 counts before the main loop runs; on 
  each loop iteration, add one to the appropriate count

- collate those results as a list of tuples for return; this involves 
  iterating over the dictionary items (which gets you the key (side) and 
  value (count)), which you can use to prepare a single tuple for that 
  side. Start by ignoring the "count as a percentage" thing and just put 
  in the count as the second tuple element; append each tuple to the 
  list

- when that returns a good result for you (like 
  [(1,3),(2,2),(3,4),(4,3)]), _then_ change the code to emit percentages 
  instead of the count. That will require a "total_count" value in order 
  to compute the percentage, and to use formatted strings to express the 
  percentage

Sketch out a function doing some or all of the above,and when you get 
stalled with a problem you can't solve, come back with the current code 
of your function, its output, and describe what you're not accomplishing 
so that we can help further.

Finally: put in lots of print() calls in your function while writing it:

    print(repr(something))

This will let you see the state of things in your function as it runs, 
which is a great aid to figuring out what may be going right or wrong.

Cheers,
Cameron Simpson <cs at cskk.id.au>