repr.py

from six import string_types
from sqlalchemy import inspect


class ReprMixin:
    __abstract__ = True

    __repr_attrs__ = []
    __repr_max_length__ = 15

    @property
    def _id_str(self):
        ids = inspect(self).identity
        if ids:
            return '-'.join([str(x) for x in ids]) if len(ids) > 1 \
                   else str(ids[0])
        else:
            return 'None'

    @property
    def _repr_attrs_str(self):
        max_length = self.__repr_max_length__

        values = []
        single = len(self.__repr_attrs__) == 1
        for key in self.__repr_attrs__:
            if not hasattr(self, key):
                raise KeyError("{} has incorrect attribute '{}' in "
                               "__repr__attrs__".format(self.__class__, key))
            value = getattr(self, key)
            wrap_in_quote = isinstance(value, string_types)

            value = str(value)
            if len(value) > max_length:
                value = value[:max_length] + '...'

            if wrap_in_quote:
                value = "'{}'".format(value)
            values.append(value if single else "{}:{}".format(key, value))

        return ' '.join(values)

    def __repr__(self):
        # get id like '#123'
        id_str = ('#' + self._id_str) if self._id_str else ''
        # join class name, id and repr_attrs
        return "<{} {}{}>".format(self.__class__.__name__, id_str,
                                  ' '+self._repr_attrs_str
                                  if self._repr_attrs_str else '')