import inspect
def get_init_params(cls):
"""Return the parameters expected when calling the class."""
initializer = cls.__init__
if initializer is object.__init__ and cls.__new__ is not object.__new__:
initializer = cls.__new__
try:
return list(inspect.signature(initializer).parameters)[1:]
except TypeError:
return None
def copiable(fields=None):
"""A class decorator factory that adds a copy method to the class.
If fields is not passed, the following a tried in order:
1. cls.__all__
2. cls._fields
3. the parameters of cls.__init__
4. the parameters of cls.__new__
"""
if isinstance(fields, type):
return copiable(None)(fields)
if isinstance(fields, str):
fields = fields.replace(',', ' ').split()
def decorator(cls):
"""Return the class after adding the copy() method."""
names = fields
if names is None:
names = getattr(cls, '__all__',
getattr(cls, '_fields',
get_init_params(cls)))
if names is None:
raise TypeError("could not determine the fields for this class.")
def copy(self, **kwargs):
"""Return a copy of this object, with updates."""
ns = dict((name, getattr(self, name)) for name in names)
ns.update(kwargs)
return type(self)(**ns)
method_name = '_copy' if 'copy' in names else 'copy'
if hasattr(cls, method_name):
raise TypeError("{!r} already exists on the class")
setattr(cls, method_name, copy)
return cls
return decorator
