scanning for numerals / letters

[Gerard Flanagan]

Kun wrote:
> I have the following if statement that checks if a form is empty:
>
>      if form.has_key("date") and form["date"].value != "":
>          date=form['date'].value
>
>      else:
>          print "ERROR: No date entered!"
>          raise Exception
>
> I would also like to add another if statement checking if 'date' has any
> letters (a-z) in it, and if so, would like to say that "you have to
> enter a date with numbers".  I am not sure how to alter my current if
> statement to do that check so any assistance would be appreciated.
>

Having just attempted a 'string_to_date' function I can see the wisdom
of having separate 'day', 'month' and 'year' input fields on the
client.  If you can't or won't provide separate fields then I suppose
you have to inform users as to what you accept as valid input, eg.
'ddmmyy', or 'month/day/year'.  Here's some code which assumes that you
are providing appropriate formatting hints:

import time
import datetime

DDMMYY = ['%d %m %Y', '%d %m %y', '%d/%m/%Y', '%d/%m/%y', '%d-%m-%Y',
'%d-%m-%y' ]

def yearmonthday(datestring, fmts=DDMMYY):
    ymd = tuple()
    for f in fmts:
        try:
            ymd = time.strptime( datestring, f )
            break
        except ValueError:
            continue
    if not ymd:
        raise ValueError
    return ymd[0], ymd[1], ymd[2]

def is_valid_date(datestring, fmts=DDMMYY):
    try:
        yearmonthday(datestring, fmts)
        return True
    except ValueError:
        return False

def string_to_date(datestring, fmts=DDMMYY):
    return datetime.date( *yearmonthday(datestring, fmts) )

assert string_to_date( '1/2/01', DDMMYY) == datetime.date(2001,2,1)
assert string_to_date( '1 2 01', DDMMYY) == datetime.date(2001,2,1)
assert string_to_date( '01/02/01', DDMMYY) == datetime.date(2001,2,1)
assert string_to_date( '1/02/2001', DDMMYY) == datetime.date(2001,2,1)
assert string_to_date( '29/02/2008', DDMMYY) ==
datetime.date(2008,2,29)
assert string_to_date( '01/2/99', DDMMYY) == datetime.date(1999,2,1)

for d in [ '', '32/1/01', '01/13/01', '29/2/07', '1/2', 'abcdef' ]:
    assert not is_valid_date(d, DDMMYY)


Gerard