Question

I am working my way through some Python tutorials one of the things that keeps coming up is user input and i just wanted to check that i am validating it correctly and not going about it the long way around.

I have written the code below and only need to ask for the day month and year but if i needed to start asking for address phone number name etc etc this would grow and grow is that normal?

def get_input( i ):

    while True:
        # We are checking the day
        if i == 'd':
            try:
                day = int( raw_input( "Please Enter the day: " ) )
                # If the day is not in range reprint
                if day > 0 and day < 32:
                    #Need to account for short months at some point
                    return day
                else:
                    print 'it has to be between 1 and 31'
            except ( ValueError ):
                print "It has to be a number!"
        elif i == 'm':
            # We are checking the month
            month = raw_input( 'Please enter ' +
                              'in words the month: '
                              ).strip().lower()
            if month in months: # use the dict we created
                return month
            else:
                print 'Please check you spelling!'
        elif i == 'y':
            # Now the year
            try:
                year = int( raw_input( "Please Enter the year" +
                                       "pad with 0's if needed: " ) )
                #make we have enough digits and a positive
                if year > 0 and len( year ) == 4:
                    return year
            except ( ValueError, TypeError ):
                    print "It has to be a four digit number!"

Answer 1

Why don’t you just have the user input the whole date in one go, and try it out to validate it?

from time import strptime

def get_date():
    while True:
        date = raw_input("Please enter a date in DD/MM/YYYY format: ")
        try:
            parsed = strptime(date, "%d/%m/%Y")
        except ValueError as e:
            print "Could not parse date: {0}".format(e)
        else:
            return parsed[:3]

year, month, day = get_date()

This will catch errors like 29/2/2011 but accept valid inputs like 29/2/2012.

If you’d like to accept several formats, just make a list of the format strings you want to accept and try them out one after another on the input, until you find one that works. But watch out for the problem of usage overloading.

For validating phone numbers I’d just go for a regexp. If you’ve never used regexps before there’s a nice python regexp howto here. Addresses are very free form, so I don’t think I’d bother validating them beyond restricting the length and doing basic security checking, especially if you’re accepting international addresses.

But in general, if there’s a python module for it you should just try to create an instance based on the input and catch the errors, like I do for the time module in the above example.

Don’t even try to validate names. Why not? Look at this article. 🙂