CODEWITHSUNDEEP
python
Will
Will

Reputation: 1

True and False Statements, finding variable types

Im trying to decide whether a string variable is a valid integer or float, ive tried try statements but using ASCII seems to be better. I can't get this to work, probably something with the returns and boolean.

def validation(valid):
 var=input("no...")
 state=True
 y=0
 for x in range(len(var)):
      if state==False or y==2:
           valid=False
           return valid
      if var[x] == chr(46) or chr(48) <= var[x] <= chr(57):
           if var[x] == chr(46):
                y+=1
           state=True
      else:
           state=False

valid=True
valid = validation(valid)
print(valid)

The ASCII characters 46 and 48-57 are a decimal point and numbers 0-9. If there more than one decimal point (representing by y) than it also returns a false statement.

Upvotes: 0

Views: 64

Answers (3)

PM 2Ring
PM 2Ring

Reputation: 55469

Your code isn't very efficient, and it doesn't handle negative numbers, or floats written in scientific notation. Using try, as in fiacre's answer is the standard way to do this in Python.

But to answer your question, you don't have a return statement after the for loop, so if all your tests succeed your function returns the default value of None. So you just need to put a return True at the end of your function.

You can make your code a little more efficient by iterating over the string values and testing the characters directly rather than indexing into the string and using chr(). Eg,

for c in var:
    if c == '.' or '0' <= c <= '9':
        # etc

Alternatively,

valid_chars = set('-.0123456789')
for c in var:
    if c in valid_chars:
        # etc

FWIW, in your existing code Python has to re-calculate chr(46) etc on every loop. Sure, that's a pretty fast operation, but it's still wasteful.

Also, there's no need to have both state and valid in the function.

Upvotes: 1

fiacre
fiacre

Reputation: 1180

There is a much simpler way to do this:

try:
    float(x)
 except ValueError as e:
    print e
    print "Not a float"
else:
   try:
       int(x)
   except ValueError as e:
       print e
       print "not an integer"

You can combine these into a method pretty easily.

Upvotes: 1

Marcin Zdunek
Marcin Zdunek

Reputation: 1011

Simple and powerful approach:

def isNum(txt):
    try:
        float(txt)
        return True
    except ValueError:
        return False

Upvotes: 2

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