regular expressions and matches

[bruno at modulix]

Johhny wrote:
> Hello,
> 
> I have recently written a small function that will verify that an IP
> address is valid. 

(snip re.match() based solution - just one remark: compiling the regexp
on each function call is more than useless)

> I was having issues trying to get my code working so that I could pass
> the IP addresses and it would return a true or false. When it matches I
> get something that looks like this.
> 
> python ip_valid.py
> IP Address : 192.158.1.1
> <_sre.SRE_Match object at 0xb7de8c80>
> 
> As I am still attempting to learn python I am interested to know how I
> could get the above to return a true or false if it matches or does not
> match the IP address.

If you re-read the fine manual, you'll notice that re.match() returns
either None or a Match object. Since, in a boolean context, None evals
to False and a Match object to True, just convert the return of re.match
to a boolean:

  return bool(re_ip.match(ipAddress))

BTW, don't mix outputs and a logic. Your validateIp() function should
*only* validate, not print anything (except for debugging purpose, but
then it should either go to a log or at least to stderr, stdout is for
normal program outputs).

> I would also like to expand that so that if the
> IP is wrong it requests the IP address again and recalls the function.

Then wrap the raw_input()/validateIp() into a loop. And wrap this loop
into a function !-)

def get_valid_ip(prompt="please enter an ip",
                 errormsg="Sorry, %s is not a valid ip"):
  while True:
    ip = raw_input("%s : " % prompt).strip()
    if validateIp(ip):
       return ip
    else:
      print errormsg % ip

ip = get_valid_ip()


> I have done the same thing in php very easily but python appears to be
> getting the better of me.

Knowledge doesn't map one-to-one from one language to another.


-- 
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb at xiludom.gro'.split('@')])"