Question

I’m writing an interpreter in Python for a very simple language grammar. I have a superclass called Statement which has several child classes. I have a method in the superclass called CreateStatement that evaluates keywords, and based on the keyword found it creates an instance of a child class object. Some of the child classes will need to call this method.

My problem is that I’m getting this error:

AttributeError: 'Statement' object has no attribute 'Assignment'

Help!

import re
from TokenHandler import TokenHandler
from ParserException import ParserException

class Statement(object):

    tokens = []
    executedTokens = []

    def __init__(self, tokenlist):
        self.tokens = tokenlist

    def getCurrentToken(self):
        print self.tokens[0]
        return self.tokens[0]

    def createStatement(self):
        currenttoken = self.getCurrentToken()

        t = TokenHandler()

        if currenttoken == "print":
            p = Print(self.tokens)
            return p

        elif t.isVariable(currenttoken):
            a = Assignment(self.tokens)
            return a

        elif currenttoken == "if":
            i = IF(self.tokens)
            return i

        elif currenttoken == "while":
            w = While(self.tokens)
            return w

        elif currenttoken == "begin":
            s = self.CompoundStatement(self.tokens)
            return s

        else:
            raise ParserException('Reserved word \'end\' expected')

    #...other methods...

---

from Statement import Statement
from TokenHandler import TokenHandler
import VariableException

class Assignment(Statement):

    def __init__(self, tokens = []):
        super(Assignment, self).__init__(tokens)

    #...other methods...

Answer 1

    a = self.Assignment(self.tokens)

is wrong if Assignment is a subclass defined at the module level and not an attribute of the Statement class or the self instance. Did you mean

    a = Assignment(self.tokens)

This line is probably similarly wrong:

    s = self.CompoundStatement(self.tokens)