File manager

def flatten(tup):
    elts = []
    for elt in tup:
        if isinstance(elt, tuple):
            elts = elts + flatten(elt)
        else:
            elts.append(elt)
    return elts

class Set:
    def __init__(self):
        self.elts = {}
    def __len__(self):
        return len(self.elts)
    def __contains__(self, elt):
        return elt in self.elts
    def add(self, elt):
        self.elts[elt] = elt
    def elements(self):
        return self.elts.keys()
    def has_elt(self, elt):
        return elt in self.elts
    def remove(self, elt):
        del self.elts[elt]
    def copy(self):
        c = Set()
        c.elts.update(self.elts)
        return c

class Stack:
    def __init__(self):
        self.stack = []
        self.pop = self.stack.pop
    def __len__(self):
        return len(self.stack)
    def push(self, elt):
        self.stack.append(elt)
    def top(self):
        return self.stack[-1]
    def __getitem__(self, index): # needed by visitContinue()
        return self.stack[index]

MANGLE_LEN = 256 # magic constant from compile.c

def mangle(name, klass):
    if not name.startswith('__'):
        return name
    if len(name) + 2 >= MANGLE_LEN:
        return name
    if name.endswith('__'):
        return name
    try:
        i = 0
        while klass[i] == '_':
            i = i + 1
    except IndexError:
        return name
    klass = klass[i:]

    tlen = len(klass) + len(name)
    if tlen > MANGLE_LEN:
        klass = klass[:MANGLE_LEN-tlen]

    return "_%s%s" % (klass, name)

def set_filename(filename, tree):
    """Set the filename attribute to filename on every node in tree"""
    worklist = [tree]
    while worklist:
        node = worklist.pop(0)
        node.filename = filename
        worklist.extend(node.getChildNodes())