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Newsgroups: comp.lang.python
Date: Fri, 22 Feb 2013 05:24:19 -0800 (PST)
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Subject: Re: Checking for valid date input and convert appropriately
From: Ferrous Cranus <nikos.gr33k@gmail.com>
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Xref: csiph.com comp.lang.python:39562

=CE=A4=CE=B7 =CE=A0=CE=B1=CF=81=CE=B1=CF=83=CE=BA=CE=B5=CF=85=CE=AE, 22 =CE=
=A6=CE=B5=CE=B2=CF=81=CE=BF=CF=85=CE=B1=CF=81=CE=AF=CE=BF=CF=85 2013 2:03:3=
9 =CE=BC.=CE=BC. UTC+2, =CE=BF =CF=87=CF=81=CE=AE=CF=83=CF=84=CE=B7=CF=82 L=
ele Gaifax =CE=AD=CE=B3=CF=81=CE=B1=CF=88=CE=B5:
> Ferrous Cranus <nikos.gr33k@gmail.com> writes:
>=20
>=20
>=20
> > I'am thinking if somehting like the follwoing work:
>=20
> >
>=20
> > if( task and ( price and price.isdigit() and price.__len__() <=3D 3 ) a=
nd ( date and eval( datetime.strptime(date, '%d %m %Y').strftime('%Y-%m-%d'=
) ) ) ):
>=20
>=20
>=20
> a) you should not (usually) call =E2=80=9Cdunder methods=E2=80=9D directl=
y, as they are
>=20
>    (usually) exposed by builtin functions::
>=20
>=20
>=20
>      obj.__len__() =3D> len(obj)
>=20
>=20
>=20
> b) what's the point of the eval() call above? When the strptime()
>=20
>    succeds, the following strftime() call always returns a string,
>=20
>    otherwise it will raise an exception and both the strftime() and the
>=20
>    outer eval() won't be called.
>=20
>=20
>=20
> Should I write the above, I'd go for having two helper functions, for
>=20
> example::=20
>=20
>=20
>=20
>   def price_is_valid(price):
>=20
>     return price and price.isdigit() and len(price) <=3D 3
>=20
>=20
>=20
>   def date_is_valid(date):
>=20
>     try:
>=20
>       datetime.strptime(date, '%d %m %Y')
>=20
>     except (TypeError, ValueError):
>=20
>       return False
>=20
>     else:
>=20
>       return True
>=20
>=20
>=20
>   ...
>=20
>=20
>=20
>   if task and price_is_valid(price) and date_is_valid(date):
>=20
>     ...
>=20
>=20
>=20
> hth,
>=20
> ciao, lele.
>=20
> --=20
>=20
> nickname: Lele Gaifax | Quando vivr=C3=B2 di quello che ho pensato ieri
>=20
> real: Emanuele Gaifas | comincer=C3=B2 ad aver paura di chi mi copia.
>=20
> lele@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 =3D 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.=20
If i surround it with eval() its still raises an excpetion.

if ( datetime.strptime(date, '%d %m %Y') ):
     date =3D 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?