On Jun 3, 11:12 am, Fdama <fsd...@gmail.com> wrote:
> I combined the int conversion and the input on the same line, rather than to
> have two different statements. But got an error message:
>
> Traceback (most recent call last):
> File "C:\Users\Faisal\Documents\python\pizza_slicer.py", line 23, in
> <module>
> start=int(input("\nStart: "))
> ValueError: invalid literal for int() with base 10: ''
>
> Could someone tell me why I got this error message?
When you were presented the 'Start' prompt, you hit Enter, which
causes `input` to return an empty string. As it's passed directly
into `int`, which requires a valid string-representing-a-number, you
get the ValueError traceback, which shows you the failing input it
received: '' This doesn't happen in your original code, because your
condition `if start:` will fail on an empty string, and not try to
turn it into an int.
You don't want to wrap your `input` with an `int`. You want to test
the return result from `input` to ensure it can be coerced:
start = input("\nStart: "))
if start and start.isdigit():
start=int(start)
...
else:
start='' # set start to empty string so the while loop repeats
Here we check that all of the characters in the string `start` are
actually numbers before coercing. This is known as the "Look Before
You Leap" (LBYL) approach. Another approach is to catch the ValueError
exception:
start = input("\nStart: "))
try:
start = int(start)
except ValueError:
start = ''
if start:
....
This is known as "Easier to for Ask Forgiveness than
Permission" (EAFP). They both have their advantages. try/excepts tends
to be quicker if few exceptions are called, while an if/else will test
every time, although at this point it's not something you need to
overly concern yourself with. Go with whichever is easiest for you to
understand & extend.
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