Python Auto sorting objects

sorteddict.py

from collections import OrderedDict
import operator


class SortedDict:
    MESSAGE_TYPEERROR = "Only the int type can be used as the key of SortedDict."
    MESSAGE_KEYERROR = "Key %d is not exist."
    MESSAGE_VALUEERROR = "%s is not in dict."

    def __init__(self, _dict=None):
        self.keys = []
        self.values = []
        self.length = 0
        if _dict:
            _dict = OrderedDict(sorted(_dict.items(), key=operator.itemgetter(0)))
            for key in _dict.keys():
                if isinstance(key, int):
                    self.keys.append(key)
                    self.values.append(_dict[key])
                    self.length += 1
                else:
                    raise TypeError(self.MESSAGE_TYPEERROR)

    def __setitem__(self, key, value):
        if isinstance(key, int):
            try:
                position = self.keys.index(key)
                self.values[position] = value
            except ValueError:
                flag = False
                for i in range(self.length):
                    if self.keys[i] > key:
                        flag = True
                        self.keys.insert(i, key)
                        self.values.insert(i, value)
                        break
                if not flag:
                    self.keys.append(key)
                    self.values.append(value)
                self.length += 1
        else:
            raise TypeError(self.MESSAGE_TYPEERROR)

    def __getitem__(self, key):
        if isinstance(key, int):
            try:
                position = self.keys.index(key)
                return self.values[position]
            except ValueError:
                raise KeyError(self.MESSAGE_KEYERROR % key)
        else:
            raise TypeError(self.MESSAGE_TYPEERROR)

    def __delitem__(self, key):
        if isinstance(key, int):
            try:
                position = self.keys.index(key)
                del self.keys[position]
                del self.values[position]
                self.length -= 1
            except ValueError:
                raise KeyError(self.MESSAGE_KEYERROR % key)
        else:
            raise TypeError(self.MESSAGE_TYPEERROR)

    def __bool__(self):
        return bool(self.keys)

    def __str__(self):
        _str = "{"
        for i in range(self.length):
            if i > 0:
                _str += ", "
            _str += "%d: %s" % (self.keys[i], repr(self.values[i]))
        _str += "}"
        return _str

    def get(self, key):
        try:
            return self.__getitem__(key)
        except KeyError:
            return None

    def keyofvalue(self, value):
        try:
            return self.keys[self.values.index(value)]
        except ValueError:
            raise ValueError(self.MESSAGE_VALUEERROR % str(value))

    def dict(self):
        _dict = OrderedDict()
        for i in range(self.length):
            _dict[self.keys[i]] = self.values[i]
        return _dict


if __name__ == "__main__":
    # Init like OrderedDict
    testdict = SortedDict({5: "test5", 1: "test1", 11: "test11", 12: "test12"})

    # Put like dict
    testdict[5] = "new_test5"
    testdict[1] = "new_test1"
    testdict[3] = "new_test3"
    testdict[25] = "new_test25"
    testdict[7] = "new_test7"

    # Delete like dict
    del testdict[11]

    # Get like dict
    print(testdict[7])
    print(testdict.get(8))

    # You can also get key of value
    print(testdict.keyofvalue("new_test5"))

    # Print like dict
    print(testdict)

    # Use like Ordered dict with this method
    print(testdict.dict())

    # You can get keys list and values list
    print(testdict.keys)
    print(testdict.values)

    # You can get length of SortedDict without len()
    print(testdict.length)

sortedlist.py

class SortedList(list):
    pass

This code has the same result and works more reliably.

    def __str__(self):
        _str = "{"
        for i in range(self.length):
            if i > 0 : _str += ", "
            _str += '%d: %s' % (self.keys[i], repr(self.values[i]))
        _str += "}"
        
        return _str

@2minchul Thanks for tip. I applied it.