Perform variable replacement of $variables in string raw using vars dictionary

def varReplace(basedir, raw, vars, lookup_fatal=True, depth=0, expand_lists=False):
    ''' Perform variable replacement of $variables in string raw using vars dictionary '''
    # this code originally from yum

    if (depth > 20):
        raise errors.AnsibleError("template recursion depth exceeded")

    done = [] # Completed chunks to return

    while raw:
        m = _varFind(basedir, raw, vars, lookup_fatal, depth)
        if not m:
            done.append(raw)
            break

        # Determine replacement value (if unknown variable then preserve
        # original)

        replacement = m['replacement']
        if expand_lists and isinstance(replacement, (list, tuple)):
            replacement = ",".join(replacement)
        if isinstance(replacement, (str, unicode)):
            replacement = varReplace(basedir, replacement, vars, lookup_fatal, depth=depth+1, expand_lists=expand_lists)
        if replacement is None:
            replacement = raw[m['start']:m['end']]

        start, end = m['start'], m['end']
        done.append(raw[:start])          # Keep stuff leading up to token
        done.append(unicode(replacement)) # Append replacement value
        raw = raw[end:]                   # Continue with remainder of string

    return ''.join(done)