Steam VDF/ACF File Parser (libraryfolders.vdf, libraryfolder.vdf, appmanifest.acf, appworkshop.acf)

# libraryfolders.vdf
# libraryfolder.vdf
# appmanifest_%d.acf
# appworkshop_%d.acf

class VDF_ParseError(Exception):
    def __init__(self, msg, line, col):
        self.msg = msg
        self.line = line
        self.col = col

    def __str__(self):
        return self.msg + " (line %d column %d)" % (self.line + 1, self.col + 1) # +1 for 0-based to 1-based

def read(path):
    """Returns dictionary of {key: value or sub}, case sensitive."""
    with open(path, "r") as f:
        escape = False
        in_quote = False
        words = []

        root = {}
        section = root
        section_history = []

        for line, row_content in enumerate(f):
            for col, c in enumerate(row_content):
                if in_quote:
                    if c in "\r\n":
                        raise VDF_ParseError("unterminated string %r" % word, line, col)
                    elif escape:
                        escape = False
                        # c is an escaped character (not handled for now)
                        words[-1] += "\\" + c
                    elif c == in_quote:
                        in_quote = False
                        if len(words) == 2:
                            key, value = tuple(words)
                            section[key] = value
                            words = []
                        elif len(words) > 2:
                            raise VDF_ParseError("expected 2 items for key and value but got %d items" % len(words), line, col)
                    elif c == "\\":
                        escape = True
                    else:
                        words[-1] += c
                elif c in "'\"":
                    in_quote = c
                    words += [""]
                elif c == "{":
                    if len(words) != 1:
                        raise VDF_ParseError("expected exactly 1 item before opening brace but got %d items" % len(words), line, col)

                    new_section = {}
                    section_history.append(section)
                    section[words[0]] = new_section
                    section = new_section
                    words = []
                elif c == "}":
                    if len(section_history) <= 0:
                        raise VDF_ParseError("closing brace not expected", line, col)
                    section = section_history.pop()
                elif not c.isspace():
                    raise VDF_ParseError("unexpected symbol %r" % c, line, col)

        if len(section_history) > 0:
            raise VDF_ParseError("%d braces left unclosed" % len(section_at)-1, line, col)

        return root

def write(f, vdf, lvl=0):
    for key, value in vdf.items():
        if type(value) is dict:
            f.write("\t"*lvl + "\"%s\"\n" % str(key))
            f.write("\t"*lvl + "{\n")
            write(f, value, lvl+1)
            f.write("\t"*lvl + "}\n")
        elif type(value) is str:
            f.write("\t"*lvl + "\"%s\"\t\t\"%s\"\n" % (str(key), str(value)))
        else:
            raise TypeError("expected dict or str not %r" % type(value))

if __name__ == "__main__":
    vdf = read(r"C:\Program Files (x86)\Steam\steamapps\libraryfolders.vdf")

    # How to use (KeyError is raised if you enter invalid key)
    print(vdf["libraryfolders"]["0"])

    # Display all
    #~ with open(1, "w") as f:
        #~ write(f, vdf)