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from importlib import import_module
from django.utils.version import get_docs_version
def deconstructible(*args, path=None):
"""
Class decorator that allows the decorated class to be serialized
by the migrations subsystem.
The `path` kwarg specifies the import path.
"""
def decorator(klass):
def __new__(cls, *args, **kwargs):
# We capture the arguments to make returning them trivial
obj = super(klass, cls).__new__(cls)
obj._constructor_args = (args, kwargs)
return obj
def deconstruct(obj):
"""
Return a 3-tuple of class import path, positional arguments,
and keyword arguments.
"""
# Fallback version
if path and type(obj) is klass:
module_name, _, name = path.rpartition(".")
else:
module_name = obj.__module__
name = obj.__class__.__name__
# Make sure it's actually there and not an inner class
module = import_module(module_name)
if not hasattr(module, name):
raise ValueError(
"Could not find object %s in %s.\n"
"Please note that you cannot serialize things like inner "
"classes. Please move the object into the main module "
"body to use migrations.\n"
"For more information, see "
"https://docs.djangoproject.com/en/%s/topics/migrations/"
"#serializing-values" % (name, module_name, get_docs_version())
)
return (
path
if path and type(obj) is klass
else f"{obj.__class__.__module__}.{name}",
obj._constructor_args[0],
obj._constructor_args[1],
)
klass.__new__ = staticmethod(__new__)
klass.deconstruct = deconstruct
return klass
if not args:
return decorator
return decorator(*args)
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