Question

I’m trying to get a number as CLI input from python. Valid input should be either an int or a float and I need to maintain type. So validating an int and returning a float wouldn’t work.

This is the best thing I’ve been able to come up with and it’s not all that good.

def is_valid(n):
    try:
        if '.' in n: return float(n)
        return int(n)
    except ValueError:
        print "try again"

def num_input(s):
    n = raw_input(s)
    while is_valid(n) is None:
        n = raw_input(s)
    return is_valid(n)

valid_num = num_input("Enter a valid number: ")

Clearly this isn’t the best way.

Answer 1

After considering the early answers and thinking about it a bit more the solution I came up with is:

def num_input(prompt, error):
    s = raw_input(prompt)
    for t in (int, float, complex):
        try: return t(s)
        except ValueError: pass
    print error
    return num_input(prompt, error) #better get it in the first 1k tries

I really want an input function not just a validation function; however, I think HYRY‘s suggestion to loop over int, float, complex is a good one. I took win‘s suggestion to use recursion instead of looping, understanding that a really confused and persistent user could exceed the max recursion depth. Although I don’t need it now, I think Karl Knechtel is correct in making the error an arg instead of hard coded.