Checking for valid date input and convert appropriately

[Ferrous Cranus]

Τη Παρασκευή, 22 Φεβρουαρίου 2013 2:03:39 μ.μ. UTC+2, ο χρήστης Lele Gaifax έγραψε:
> Ferrous Cranus <nikos.gr33k at gmail.com> writes:
> 
> 
> 
> > I'am thinking if somehting like the follwoing work:
> 
> >
> 
> > if( task and ( price and price.isdigit() and price.__len__() <= 3 ) and ( date and eval( datetime.strptime(date, '%d %m %Y').strftime('%Y-%m-%d') ) ) ):
> 
> 
> 
> a) you should not (usually) call “dunder methods” directly, as they are
> 
>    (usually) exposed by builtin functions::
> 
> 
> 
>      obj.__len__() => len(obj)
> 
> 
> 
> b) what's the point of the eval() call above? When the strptime()
> 
>    succeds, the following strftime() call always returns a string,
> 
>    otherwise it will raise an exception and both the strftime() and the
> 
>    outer eval() won't be called.
> 
> 
> 
> Should I write the above, I'd go for having two helper functions, for
> 
> example:: 
> 
> 
> 
>   def price_is_valid(price):
> 
>     return price and price.isdigit() and len(price) <= 3
> 
> 
> 
>   def date_is_valid(date):
> 
>     try:
> 
>       datetime.strptime(date, '%d %m %Y')
> 
>     except (TypeError, ValueError):
> 
>       return False
> 
>     else:
> 
>       return True
> 
> 
> 
>   ...
> 
> 
> 
>   if task and price_is_valid(price) and date_is_valid(date):
> 
>     ...
> 
> 
> 
> hth,
> 
> ciao, lele.
> 
> -- 
> 
> nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
> 
> real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
> 
> lele at metapensiero.it  |                 -- Fortunato Depero, 1929.

Let me ask it like this:
How can i avoid using try: except: for checkign the date but instead check it with an if statement:

if ( datetime.strptime(date, '%d %m %Y') ):
     date = datetime.strptime(date, '%d %m %Y').strftime('%Y-%m-%d')
else:
     print( "Date wasn't entered properly" )

I'am trying this but if user entered date is noit on the acceptible format it raises an exception. 
If i surround it with eval() its still raises an excpetion.

if ( datetime.strptime(date, '%d %m %Y') ):
     date = datetime.strptime(date, '%d %m %Y').strftime('%Y-%m-%d')
else:
     print( "Date wasn't entered properly" )

How can i write that with an if suppresing the errors if any?