[Tutor] taking support of strings in solving numerical problems

[Manprit Singh]

Dear Sir,
While working on your suggestions and doing experiments on interpreter, I
found an unexpected behaviour as follows :

>>> def genfx_ser(x, lim):
            sum_no = x
            for i in range(lim):
                yield sum_no
                sum_no = (sum_no*10) + x


>>> genfx_ser
<function genfx_ser at 0x7f38bff14c10>
>>> genfx_ser(9, "a")
<generator object genfx_ser at 0x7f38bf690190>

In the second  function call , see the second argument is "a", which is
being passed to formal parameter  lim  in function definition, must create
an error , since range cannot accept a non integer value, but still
function call is returning a generator object.

Is it a bug ?

Similarly i tried for some other values as  given below :

>>> genfx_ser(9, 0)
<generator object genfx_ser at 0x7f38bf64e510>

That again returned a generator object with a second argument to the call
equals 0 .

Kindly put some light on it

Regards
Manprit Singh




On Sun, Oct 25, 2020 at 1:30 PM Alan Gauld via Tutor <tutor at python.org>
wrote:

> On 25/10/2020 02:52, Manprit Singh wrote:
>
> > def genfx_ser(x, lim):
> >         sum_no = x
> >         for i in range(lim):
> >             yield sum_no
> >             sum_no = (sum_no*10) + x
> >
> > This feels more good to me . Now reason of putting yield inside for loop
> > is, let's say if someone tries to find the sum of series upto 0 terms by
> > writing sum(genfx_series(9, 0)), He or she will get 0 as sum as there
> will be no
> > data in the iterator returned by generator function at that time.
>
> The logic on yield is good, but if the loop is not entered
> the user gets None returned(the default value) not 0.
> These are different values.
>
> You really should put a return 0 in an if test for that scenario.
>
> if lim == 0: return 0
>
> Programming conventions suggest that should in fact be the first
> line of the function because its good practice to check  for
> invalid or edge case input before handling the normal case.
>
> However a better solution, rather than handing back a number
> with special meaning would be to throw an exception - ValueError
> being the obvious choice. So the first line of the function
> could be:
>
> if lim <= 0: raise ValueError("lim must be greater than zero")
>
> You might like to check that x is an int too.... Or try
> converting it to an int.
>
> > Need your humble suggestions on this example using generator functions .
>
> It's a  reasonable use case for a generator since lim could potentially
> be a large value.
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.amazon.com/author/alan_gauld
> Follow my photo-blog on Flickr at:
> http://www.flickr.com/photos/alangauldphotos
>
>
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