Python is reading one of my classes in as a variable and giving a reference error

Question

I have an if/elif statement that appends objects into a stack. The code works fine for the first 3 parts of the statement but is giving errors for the else part. I've tried a few different things but they just end up giving more errors. Thanks in advance for any help!

class nfa:
    intial, accept = None, None

    def __init__(self, initial, accept):
      self.intial, self.accept = initial, accept

def compile(postfix):
    nfaStack = []

    for c in postfix:
        # join the initial and accept states together to create a loop for your characters
        if c == '*':
            nfa = nfaStack.pop()
            initial, accept = state(), state()

            initial.edge1, nfa.accept.edge1 = nfa.intial
            initial.edge2, nfa.accept.edge2 = accept, accept
            nfaStack.append(nfa(initial, accept))
        # merge the two automata by linking 1's accept to 2's initial states
        elif c == '.': 
            nfa2, nfa1 = nfaStack.pop(), nfaStack.pop()
            nfa1.accept.edge1 = nfa2.intial
            nfaStack.append(nfa1.intial, nfa2.accept)       
        # create new initial and accept states and use them to link nfa1 and nfa2
        elif c == '|':
            nfa2, nfa1 = nfaStack.pop(), nfaStack.pop()
            initial, accept = state(), state()
            initial.edge1, initial.edge2 = nfa1.intial, nfa2.intial
            # both old accept states now point to our new accept state
            nfa1.accept.edge1, nfa2.accept.edge1 = accept, accept
            nfaStack.append(nfa(initial, accept))      
        # creates new states and edges; labels each edge with what the current non-special character is
        else:
            initial, accept = state(), state()
            initial.label = c
            initial.edge1 = accept
            # create instance of class nfa()
            nfaStack.append(nfa(initial, accept))   
    # should only ever have one nfa in the stack
    return nfaStack.pop()

Answer 1

You're getting this error because you're accidentally redefining nfa as a variable here:

# join the initial and accept states together to create a loop for your characters
if c == '*':
    nfa = nfaStack.pop() # `nfa` is now a variable!

The simplest solution is to capitalize the class to NFA, so it's clear what is a variable and what is a class name. That would mean changing lines like this:

# This:
nfaStack.append(nfa(initial, accept))
# Becomes:
nfaStack.append(NFA(initial, accept))