I'm Sure There's A Better Way

[Tim Daneliuk]

I want a function to check a string to make sure it is a legitimate
dollar amount.  Which means it follows these rules:

First character is numeric or "-"
At most, one "." is allowed and, if present, is followed by exactly two digits
All the remaining characters must be in the range "0" - "9"


I wrote the attached to check a string for these rules, but I can't help
wondering if my feeble newbie python coding isn't already better done
elswhere and/or using existing logic.  Any ideas all?  TIA.... Code follows -



# Check and see if passed string is a legit amount

def IsNum(num):
    if num == "":
        return FALSE
    digits = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "."]
    z = num.split(".")
    if len(z) > 2:             # At Most, only once decimal permitted.
        return FALSE
    if len(z) == 2:
        if len(z[1]) != 2: # Exactly two digits must follow decimal
            return FALSE
    if (num[0] == '-') and (len(num) > 1): # 1st char can be sign if more chars follow
        num = num[1:]    # Drop sign for purposes of checking
    for x in num:        # Make sure all chars are legit digits
        if not digits.count(x):
            return FALSE
    return TRUE

-- 
------------------------------------------------------------------------------
Tim Daneliuk
tundra at tundraware.com