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Direktori : /opt/alt/python37/lib64/python3.7/site-packages/pyrsistent/ |
Current File : //opt/alt/python37/lib64/python3.7/site-packages/pyrsistent/_immutable.py |
import sys import six def immutable(members='', name='Immutable', verbose=False): """ Produces a class that either can be used standalone or as a base class for persistent classes. This is a thin wrapper around a named tuple. Constructing a type and using it to instantiate objects: >>> Point = immutable('x, y', name='Point') >>> p = Point(1, 2) >>> p2 = p.set(x=3) >>> p Point(x=1, y=2) >>> p2 Point(x=3, y=2) Inheriting from a constructed type. In this case no type name needs to be supplied: >>> class PositivePoint(immutable('x, y')): ... __slots__ = tuple() ... def __new__(cls, x, y): ... if x > 0 and y > 0: ... return super(PositivePoint, cls).__new__(cls, x, y) ... raise Exception('Coordinates must be positive!') ... >>> p = PositivePoint(1, 2) >>> p.set(x=3) PositivePoint(x=3, y=2) >>> p.set(y=-3) Traceback (most recent call last): Exception: Coordinates must be positive! The persistent class also supports the notion of frozen members. The value of a frozen member cannot be updated. For example it could be used to implement an ID that should remain the same over time. A frozen member is denoted by a trailing underscore. >>> Point = immutable('x, y, id_', name='Point') >>> p = Point(1, 2, id_=17) >>> p.set(x=3) Point(x=3, y=2, id_=17) >>> p.set(id_=18) Traceback (most recent call last): AttributeError: Cannot set frozen members id_ """ if isinstance(members, six.string_types): members = members.replace(',', ' ').split() def frozen_member_test(): frozen_members = ["'%s'" % f for f in members if f.endswith('_')] if frozen_members: return """ frozen_fields = fields_to_modify & set([{frozen_members}]) if frozen_fields: raise AttributeError('Cannot set frozen members %s' % ', '.join(frozen_fields)) """.format(frozen_members=', '.join(frozen_members)) return '' verbose_string = "" if sys.version_info < (3, 7): # Verbose is no longer supported in Python 3.7 verbose_string = ", verbose={verbose}".format(verbose=verbose) quoted_members = ', '.join("'%s'" % m for m in members) template = """ class {class_name}(namedtuple('ImmutableBase', [{quoted_members}]{verbose_string})): __slots__ = tuple() def __repr__(self): return super({class_name}, self).__repr__().replace('ImmutableBase', self.__class__.__name__) def set(self, **kwargs): if not kwargs: return self fields_to_modify = set(kwargs.keys()) if not fields_to_modify <= {member_set}: raise AttributeError("'%s' is not a member" % ', '.join(fields_to_modify - {member_set})) {frozen_member_test} return self.__class__.__new__(self.__class__, *map(kwargs.pop, [{quoted_members}], self)) """.format(quoted_members=quoted_members, member_set="set([%s])" % quoted_members if quoted_members else 'set()', frozen_member_test=frozen_member_test(), verbose_string=verbose_string, class_name=name) if verbose: print(template) from collections import namedtuple namespace = dict(namedtuple=namedtuple, __name__='pyrsistent_immutable') try: six.exec_(template, namespace) except SyntaxError as e: raise SyntaxError(e.message + ':\n' + template) return namespace[name]