unexplainable python

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When creating a script that converts digits to words I've come across
some unexplainable python. The script works fine until I use a 5 digit
number and get a 'IndexError: string index out of range'. After
looking into it and adding some print calls, it looks like a variable
changes for no reason. The example beneath is using the digits 34567,
the _5digit function slices 34 off and passes it to the _2digit
function, which works with 2 digit strings but the IndexError is
raised. Please accept my apologies for the explanation, I'm finding it
hard to put into words. Has anyone any idea why it's acting the way it
is?

enter number: 34567
_5digit function used
34 before sent to _2digit
34 slice when at _2digit function
34 before sent to plus_ten function
7 slice when at _2digit function
7 before sent to plus_ten function


from __future__ import print_function
import sys

class number(object):

    def __init__(self, number):

        #remove any preceding zero's
        num = int(number)
        self.num = str(num)
        self.num = number

        self.single =
{'0':'zero','1':'one','2':'two','3':'three','4':'four',
 
'5':'five','6':'six','7':'seven','8':'eight','9':'nine'}
        self.teen = {'11':'eleven','12':'twelve','13':'thirteen',
                      '14':'fourteen','15':'fifteen','16':'sixteen',
 
'17':'seventeen','18':'eighteen','19':'nineteen'}
        self.plus_ten =
{'10':'ten','20':'twenty','30':'thirty','40':'forty',
                          '50':'fifty','60':'sixty','70':'seventy',
                          '80':'eighty','90':'ninety'}
        self._translate()

    def _translate(self):

        fns = [ i for i in number.__dict__ if 'digit' in i ]
        fns.sort()
        fn_name = fns[len(self.num)-1]
        print(fn_name,'function used')
        fn = number.__dict__[fn_name]
        print(fn(self, self.num))


    def _1digit(self, n):

        return self.single[n]

    def _2digit(self, n):

        print(n, 'slice when at _2digit function')
        if '0' in self.num:
            return self.plus_ten[n]
        elif self.num[0] == '1':
            return self.teen[n]
        else:
            print(n,'before sent to plus_ten function')
            var = self.plus_ten[n[0]+'0'] + ' ' + self._1digit(n[1])
            return var

    def _3digit(self, n):

        var = self._1digit(n[0]) + ' hundred and ' + self._2digit(n
[1:])
        return var

    def _4digit(self, n):

        var = self._1digit(n[0]) + ' thousand ' + self._3digit(n[1:])
        return var


    def _5digit(self, n):

        print(n[:2],'before sent to _2digit')
        var = self._2digit(n[:2]) + ' thousand ' + self._4digit(n[2:])
        return var

class control(object):

    def __init__(self):
        pass

    def data_input(self):


        while True:
            i = raw_input('enter number: ')
            if i == 's':
                break
            #try:
            n = number(i)
            #except:
            #    print('not a number')


if __name__ in '__main__':
    c = control()
    c.data_input()