[Python] Python: Maximum recursion depth while getting the str of an object

I'm making a program to get the amount of letters in a number:

def convert(number):
lettercount = 0

numstr = str(number)

# One's places
if len(numstr) is 1:
if number == 1 or number == 2 or number == 6:
lettercount += 3

elif number == 4 or number == 5 or number == 9:
lettercount += 4

else:
lettercount += 5

# Ten's places
elif len(numstr) is 2:
if number == 10:
lettercount += 3

elif number == 11 or number == 12:
lettercount += 6

elif number == 15 or number == 16:
lettercount += 7

elif number == 13 or number == 14 or number == 19:
lettercount += 8

elif number == 17 or number == 18:
lettercount += 9

elif number == 20 or number == 30 or number == 40 or\
number == 80 or number == 90:
lettercount += 6

else:
lettercount += convert(int((numstr)[-1]))
lettercount += convert(int(round(number, -1)))

return lettercount

print "88 has %i letters in its name." % convert(88)
print "23 has %i letters in its name." % convert(23)
print "46 has %i letters in its name." % convert(46)


It works just fine and returns a correct response for the 88 and 23, but it gives a recursion depth error on 46. I'm confused; why does it happen on just 46?


Fixed code:

def convert(number):
lettercount = 0

numstr = str(number)

# One's places
if len(numstr) == 1:
if number == 1 or number == 2 or number == 6:
lettercount += 3

elif number == 4 or number == 5 or number == 9:
lettercount += 4

else:
lettercount += 5

# Ten's places
elif len(numstr) == 2:
if number == 10:
lettercount += 3

elif number == 40 or number == 50:
lettercount += 5

elif number == 11 or number == 12 or number == 20 or number == 30 or\
number == 80 or number == 90:
lettercount += 6

elif number == 15 or number == 16:
lettercount += 7

elif number == 13 or number == 14 or number == 19:
lettercount += 8

elif number == 17 or number == 18:
lettercount += 9

else:
lettercount += convert(int((numstr)[-1]))
lettercount += convert((int(numstr) // 10) * 10)

return lettercount

print "88 has %i letters in its name." % convert(88)
print "23 has %i letters in its name." % convert(23)
print "46 has %i letters in its name." % convert(46)

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