[Tutor] TypeError I don't understand

[Vincent Wan]

Dear All,

python gives me a type error that I don't understand

running my program gives me "TypeError: len() of unsized object"
but I know I that the object whose length I asked for is a list and  
therefor a sized type

here is a sample of the output:

type (living_species) : <type 'list'>
len(living_species) : 1
Traceback (most recent call last):
   File "new_prog1b.txt", line 15, in ?
     while counter < len(living_species):
TypeError: len() of unsized object

here is the code:

import random

living_species = [0]
dead_species = []
tree = "*0*"

current_time = 0
end_of_time = 25
current_species = 0
branching_probablity = .1
extinction_probablity = .1

while current_time < end_of_time:
     counter = 0
     while counter < len(living_species):
         if random.random() < branching_probablity:
             current_species += 1
             living_species.append(current_species)
             target = '*' + str(living_species[counter]) + '*'
             replacement = '(' + target + ',*' + str(current_species) +  
'*)'
             tree = tree.replace(target, replacement)
         counter += 1
     # PROBLEM HERE
     print 'type (living_species) :',type(living_species)     # proves  
living_species is a list
     print 'len(living_species) :', len(living_species)    # proves  
length living_species is a number
     counter = len(living_species) - 1    # python says TypeError: len()  
of unsized object
     while counter >- 1:
         if random.random() < extinction_probablity:
             dead_species = dead_species.append(counter)
             living_species = living_species.remove(counter)
         counter -= 1
     current_time += 1

print living_species
print dead_species
tree = tree.replace('*','')
print tree

Thank You,

Vincent

------------------------------------------------------------------------ 
--------------
PhD Candidate
Committee on the Conceptual and Historical Studies of Science
University of Chicago

PO Box 73727
Fairbanks, AK 99707

wanATwalrusDOTus (replace AT with "@" and dot with ".")