Dichotomous Key

import csv

class dichotomousKey(object):
    def __init__(self, steps = []):
        self.steps = steps

    def load(self, file_name):
        with open(file_name + '.txt') as csv_file:
            csv_reader = csv.reader(csv_file, delimiter='|')
            line_count = 0
            for row in csv_reader:
                if line_count == 0:
                    self.unpack(row)
                    line_count += 1
                else:
                    self.unpack(row)
                    line_count += 1

    def unpack(self, row):
        if len(row) == 4:
            level, argument, goto, organism = row
            return self.steps.append(Step(level, argument, goto, organism))
        if len(row) == 3:

            level, argument, goto = row
            return self.steps.append(Step(level, argument, goto))

    def execute(self, level):
        print(self.steps[level].level + 'a : ' + self.steps[level].argument)
        print(self.steps[level + 1].level + 'b : ' + self.steps[level + 1].argument)
        choice = str(input("<a/b> "))
        print()
        if choice.lower() == 'a':
            if self.steps[level].has_organism():
                print("Your organism is: %s" % (self.steps[level].organism))
            else:
                self.execute(self.steps[level].get_list_index(self.steps[level].goto))
        elif choice.lower() == 'b':
            if self.steps[level + 1].has_organism():
                print("Your organism is: %s" % (self.steps[level + 1].organism))
            else:
                self.execute(self.steps[level + 1].get_list_index(self.steps[level + 1].goto))
        else:
            print("Error, Invalid Input!")

class Step(object):
    def __init__(self, level=None, argument=None, goto=None, organism=None):
        self.level = level
        self.argument = argument
        self.goto = goto
        self.organism = organism

    def has_organism(self):
        if self.organism:
            return True

    def get_list_index(self, goto):
        return (int(goto) * 2) - 2

def main():
    d_key = dichotomousKey()
    d_key.load('dichotomous')
    d_key.execute(0)
    input()

main()

#SAMPLE TEXT FILE
'''
Vertebrate Dichotomous Key

1|It has fur.|0|Mammals
1|It has no fur.|2

2|It has feathers.|0|Birds
2|It has no feathers.|3

3|It has dry skin.|0|Reptiles
3|It has moist skin|4

4|It has scales|0|Fish
4|It has no scales|0|Amphibians
'''