Translate Tcl List to Python List

I try to translate Tcl list to python list.

There are two problems:

• If a list in the original list contains only a single list, the translation is incorrect. For example, {{12 34}} is not correctly translated.
• The option to convert all numbers to a type does not work.

Python 3 code:

import tkinter


class TclInterpreter(object):
    def __init__(self):
        self._tcl = tkinter.Tcl()

    def eval(self, tcl_cmd):
        return self._tcl.eval(tcl_cmd)


class TclPyListTranslator(object):
    def __init__(self, tcl):
        self._tcl = tcl

    def to_py(self, tcl_list, dtype=str):
        # convert a Tcl List to python list, also convert elements of each leaf
        # node to dtype
        self._tcl.eval("set tcl_list %s" % tcl_list)
        numItems = int(self._tcl.eval("llength $tcl_list"))
        if numItems > 1:
            result = [self._tcl.eval("lindex $tcl_list %d" % i) for i in range(
                numItems)]
            for i in range(numItems):
                result[i] = self.to_py("{" + result[i] + "}", dtype)
        else:
            result = dtype(self._tcl.eval("lindex $tcl_list %d" % 0))
        return result


inter = TclInterpreter()
translator = TclPyListTranslator(inter)
tcl_list = "{12 {{12 34}} {56 {78 {11 12} 10}}}"

# prints ['12', '12 34', ['56', ['78', ['11', '12'], '10']]]
# The '12 34' is incorrect
print(translator.to_py(tcl_list))

# does not run
print(translator.to_py(tcl_list, int))

Python parser:

def add_element(cache, element):
    if element != '':
        cache[-1].append(element)
    return ''

def parse(tcl_list):
    """ Parse TCL list to Python list """    
    out = []
    cache = [out]
    element = ''
    escape = False
    for char in tcl_list:
        if escape:
            element += char
            escape = False
        elif char == "\\":
            escape = True
        elif char in [" ", "\t", "\r", "\n"]:
            element = add_element(cache, element)
        elif char == "{":
            a = []
            cache[-1].append(a)
            cache.append(a)
        elif char == "}":
            element = add_element(cache, element)
            cache.pop()
        else:
            element += char
    return out[0]
import pprint
pprint.pprint(
    parse("{ 12 apple {100} {} {{12 34}} \n {56\n { \\{78 {11 12 11} 10}}}"))

output:

['12',
 'apple',
 ['100'],
 [],
 [['12', '34']],
 ['56', ['{78', ['11', '12', '11'], '10']]]