len(list) in python returns 1 instead of 0

Question

We are trying to count the instances in glassfish. When using the len() function this always returns 1 instead of 0. Maybe it fills the list[0] with an empty space or something. This is our code.

    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    ssh.connect(self.get('hostname'),int(self.get('port')),self.get('username'),allow_agent=True)
    #try:
    stdin, stdout, stderr = ssh.exec_command('~/glassfish3/glassfish/bin/asadmin list-instances')
    result = stdout.readlines()
    #except Exception, e:
    #   return MonitoringResult(MonitoringResult.OK,'all instances up!')
    result = "".join(result)
    #line = re.compile(r'\bnot\s\D*\n')

    #rline = "".join(line.findall((result)))
    line2=re.compile(r'\bnot')
    rline2 = ";".join(line2.findall((result)))
    print(rline2)
    i = 0
    listr = rline2.split(";")

    while(i < (len(listr)):
        i+=1
    print(i)

    if rline2:
        return MonitoringResult(MonitoringResult.CRITICAL,'instance down')
    else:
        return MonitoringResult(MonitoringResult.OK, 'All instances are up')

Answer 1

The result of str.split cannot be an empty list:

>>> ''.split(';')
['']

If you want to check whether the list obtained contains any non-empty string, use any:

>>> any(''.split(';'))
False
>>> any('a;'.split(';'))
True
>>> ';'.split(';')
['', '']
>>> any(';'.split(';'))
False

If you want to filter out the empty strings, use filter:

>>> filter(None, ';'.split(';'))
[]

Or a list-comprehension:

>>> [s for s in ';'.split(';') if s]
[]

---

I just realized that str.split can return an empty list. But only when called without an argument:

>>> ''.split()
[]
>>> '    '.split()   #white space string
[]

The explanation is in the documentation:

S.split([sep [,maxsplit]]) -> list of strings

Return a list of the words in the string S, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done. If sep is not specified or is None, any whitespace string is a separator and empty strings are removed from the result.