When working on essentially a custom enumerated type implementation, I ran into a situation where it appears I had to derive separate yet almost identical subclasses from both int and long since they're distinct classes in Python. This seems kind of ironic since instances of the two can usually be used interchangeably because for the most part they're just created automatically whenever required.
What I have works fine, but in the spirit of DRY (Don't Repeat Yourself), I can't help but wonder if there isn't any better, or at least a more succinct, way to accomplish this. The goal is to have subclass instances that can be used everywhere -- or as close to that as possible -- that instances of their base classes could have been. Ideally this should happen automatically similar to the way the built-in int() actually returns a long whenever it detects one is required.
Here's my current implementation:
class NamedInt(int):
"""Subclass of type int with a name attribute"""
__slots__ = "_name" # also prevents additional attributes from being added
def __setattr__(self, name, value):
if hasattr(self, name):
raise AttributeError(
"'NamedInt' object attribute %r is read-only" % name)
else:
raise AttributeError(
"Cannot add attribute %r to 'NamedInt' object" % name)
def __new__(cls, name, value):
self = super(NamedInt, NamedInt).__new__(cls, value)
# avoid call to this subclass's __setattr__
super(NamedInt, self).__setattr__('_name', name)
return self
def __str__(self): # override string conversion to be name
return self._name
__repr__ = __str__
class NamedLong(long):
"""Subclass of type long with a name attribute"""
# note: subtypes of variable length 'long' type can't have __slots__
def __setattr__(self, name, value):
if hasattr(self, name):
raise AttributeError(
"NamedLong object attribute %r is read-only" % name)
else:
raise AttributeError(
"Cannot add attribute %r to 'NamedLong' object" % name)
def __new__(cls, name, value):
self = super(NamedLong, NamedLong).__new__(cls, value)
# avoid call to subclass's __setattr__
super(NamedLong, self).__setattr__('_name', name)
return self
def __str__(self):
return self._name # override string conversion to be name
__repr__ = __str__
class NamedWholeNumber(object):
"""Factory class which creates either a NamedInt or NamedLong
instance depending on magnitude of its numeric value.
Basically does the same thing as the built-in int() function
does but also assigns a '_name' attribute to the numeric value"""
class __metaclass__(type):
"""NamedWholeNumber metaclass to allocate and initialize the
appropriate immutable numeric type."""
def __call__(cls, name, value, base=None):
"""Construct appropriate Named* subclass."""
# note the int() call may return a long (it will also convert
# values given in a string along with optional base argument)
number = int(value) if base is None else int(value, base)
# determine the type of named numeric subclass to use
if -sys.maxint-1 <= number <= sys.maxint:
named_number_class = NamedInt
else:
named_number_class = NamedLong
# return instance of proper named number class
return named_number_class(name, number)
Here's how you can solve the DRY issue via multiple inheritance. Unfortunately, it doesn't play well with __slots__ (it causes compile-time TypeErrors) so I've had to leave that out. Hopefully the __dict__ values won't waste too much memory for your use case.
class Named(object):
"""Named object mix-in. Not useable directly."""
def __setattr__(self, name, value):
if hasattr(self, name):
raise AttributeError(
"%r object attribute %r is read-only" %
(self.__class__.__name__, name))
else:
raise AttributeError(
"Cannot add attribute %r to %r object" %
(name, self.__class__.__name__))
def __new__(cls, name, *args):
self = super(Named, cls).__new__(cls, *args)
super(Named, self).__setattr__('_name', name)
return self
def __str__(self): # override string conversion to be name
return self._name
__repr__ = __str__
class NamedInt(Named, int):
"""NamedInt class. Constructor will return a NamedLong if value is big."""
def __new__(cls, name, *args):
value = int(*args) # will raise an exception on invalid arguments
if isinstance(value, int):
return super(NamedInt, cls).__new__(cls, name, value)
elif isinstance(value, long):
return NamedLong(name, value)
class NamedLong(Named, long):
"""Nothing to see here."""
pass
Overriding the allocator will let you return an object of the appropriate type.
class NamedInt(int):
def __new__(...):
if should_be_NamedLong(...):
return NamedLong(...)
...
Here's a class decorator version:
def named_number(Named):
#staticmethod
def __new__(cls, name, value, base=None):
value = int(value) if base is None else int(value, base)
if isinstance(value, int):
NamedNumber = Named # NamedInt / NamedLong
else:
NamedNumber = cls = NamedLong
self = super(NamedNumber, cls).__new__(cls, value)
super(NamedNumber, self).__setattr__('_name', name)
return self
def __setattr__(self, name, value):
if hasattr(self, name):
raise AttributeError(
"'%r' object attribute %r is read-only" % (Named, name))
else:
raise AttributeError(
"Cannot add attribute %r to '%r' object" % (name, Named))
def __repr__(self):
return self._name
__str__ = __repr__
for k, v in locals().items():
if k != 'Named':
setattr(Named, k, v)
return Named
#named_number
class NamedInt(int):
__slots__ = '_name'
#named_number
class NamedLong(long): pass
Related
Goal
I try to implement a Decorator that could act like a typechecking function. I'm not there yet since the validation is working well but when I try to access the attribute I get the error : TypeError: __get__() takes 2 positional arguments but 3 were given.
I'm using Python 3.9.7.
Description
# Descriptor definition
class PositiveNumber:
def __get__(self, obj):
return self.value
def __set__(self, obj, value):
if not isinstance(value, (int, float)):
raise TypeError('value must be a number')
if value < 0:
raise ValueError('Value cannot be negative.')
self.value = value
# Decorator definition
def positive_number(attr):
def decorator(cls):
setattr(cls, attr, PositiveNumber())
return cls
return decorator
# class that actually check for the right type
#positive_number('number')
class MyClass(object):
def __init__(self, value):
self.number = value
def main():
a = MyClass(3)
print(a.number)
if __name__ == '__main__':
main()
Do you see the way to fix this ?
You got the signature wrong. When the __get__ is called, 3 arguments are passed (including the type whether you use it or not):
class PositiveNumber:
def __get__(self, obj, objtype=None):
return self.value
# ...
The other thing that is wrong: there is only one descriptor instance, so all instances of MyClass will share that object's value attribute!
a = MyClass(3)
b = MyClass(5)
a.number
# 5
So you better fix this associating the set values with the instances:
class PositiveNumber:
def __get__(self, obj, objtype=None):
return obj._value
def __set__(self, obj, value):
if not isinstance(value, (int, float)):
raise TypeError('value must be a number')
if value < 0:
raise ValueError('Value cannot be negative.')
obj._value = value
You could also use a more specific attribute name in accordance with the name of the field on the actual class:
class PositiveNumber:
def __set_name__(self, owner, name):
self.private_name = '_' + name # e.g. "_number"
def __get__(self, obj, objtype=None):
return getattr(obj, self.private_name)
def __set__(self, obj, value):
if not isinstance(value, (int, float)):
raise TypeError('value must be a number')
if value < 0:
raise ValueError('Value cannot be negative.')
setattr(obj, self.private_name, value)
The set_name method is only called when the descriptor is already there upon class creation. That means you cannot set it dynamically with setattr on the already existing class object, but you have to create a new class!
def positive_number(attr):
def decorator(cls):
return type(cls.__name__, (cls,), {attr: PositiveNumber()})
return decorator
In a class I am writing, one of the member properties is a list:
#property
def address_list(self):
return self._address_list
#address_list.setter
def address_list(self, addr_list):
if type(addr_list) is not list:
return
self._address_list = addr_list
I want to be able to write a property so if someone wanted to append something onto the list, it would call something like another setter function, but for adding onto the list:
Object.address_list.append(value)
would call something like
#property.appender # I made this line up
def address_list.append(self, value):
if value >= 0 and value <= 127:
self._address_list.append(value)
so I could safely append values to my private list. Is something like this possible without having to create a new type of list object?
EDIT: Address list returns a standard python list
you would need to create a new AddressList class to handle this. something like
class Wrapper(object):
"""Wrapper class that provides proxy access to an instance of some
internal instance."""
__wraps__ = None
__ignore__ = "class mro new init setattr getattr getattribute"
def __init__(self, obj):
if self.__wraps__ is None:
raise TypeError("base class Wrapper may not be instantiated")
elif isinstance(obj, self.__wraps__):
self._obj = obj
else:
raise ValueError("wrapped object must be of %s" % self.__wraps__)
# provide proxy access to regular attributes of wrapped object
def __getattr__(self, name):
return getattr(self._obj, name)
# create proxies for wrapped object's double-underscore attributes
class __metaclass__(type):
def __init__(cls, name, bases, dct):
def make_proxy(name):
def proxy(self, *args):
return getattr(self._obj, name)
return proxy
type.__init__(cls, name, bases, dct)
if cls.__wraps__:
ignore = set("__%s__" % n for n in cls.__ignore__.split())
for name in dir(cls.__wraps__):
if name.startswith("__"):
if name not in ignore and name not in dct:
setattr(cls, name, property(make_proxy(name)))
class AddressList(Wrapper):
__wraps__=list
def append(self,x):
if 0 <= x <= 127:
self._obj.append(x)
else:
raise ValueError("Cannot append %r"%x)
class MyContainer:
def __init__(self):
self.address_list = AddressList([])
x = MyContainer()
x.address_list.append(1)
x.address_list.append(7)
x.address_list.append(-1)
print x.address_list
*note that this answer borrows heavily from https://stackoverflow.com/a/9059858/541038 *
I would like to define metaclass that will enable me to create properties (i.e. setter, getter) in new class on the base of the class's attributes.
For example, I would like to define the class:
class Person(metaclass=MetaReadOnly):
name = "Ketty"
age = 22
def __str__(self):
return ("Name: " + str(self.name) + "; age: "
+ str(self.age))
But I would like to get something like this:
class Person():
__name = "Ketty"
__age = 22
#property
def name(self):
return self.__name;
#name.setter
def name(self, value):
raise RuntimeError("Read only")
#property
def age(self):
return self.__age
#age.setter
def age(self, value):
raise RuntimeError("Read only")
def __str__(self):
return ("Name: " + str(self.name) + "; age: "
+ str(self.age))
Here is the metaclass I have written:
class MetaReadOnly(type):
def __new__(cls, clsname, bases, dct):
result_dct = {}
for key, value in dct.items():
if not key.startswith("__"):
result_dct["__" + key] = value
fget = lambda self: getattr(self, "__%s" % key)
fset = lambda self, value: setattr(self, "__"
+ key, value)
result_dct[key] = property(fget, fset)
else:
result_dct[key] = value
inst = super(MetaReadOnly, cls).__new__(cls, clsname,
bases, result_dct)
return inst
def raiseerror(self, attribute):
raise RuntimeError("%s is read only." % attribute)
However it dosen't work properly.
client = Person()
print(client)
Sometimes I get:
Name: Ketty; age: Ketty
sometimes:
Name: 22; age: 22
or even an error:
Traceback (most recent call last):
File "F:\Projects\TestP\src\main.py", line 38, in <module>
print(client)
File "F:\Projects\TestP\src\main.py", line 34, in __str__
return ("Name: " + str(self.name) + "; age: " + str(self.age))
File "F:\Projects\TestP\src\main.py", line 13, in <lambda>
fget = lambda self: getattr(self, "__%s" % key)
AttributeError: 'Person' object has no attribute '____qualname__'
I have found example how it can be done other way Python classes: Dynamic properties, but I would like to do it with metaclass. Do you have any idea how this can be done or is it possible at all ?
Bind the current value of key to the parameter in your fget and fset definitions:
fget = lambda self, k=key: getattr(self, "__%s" % k)
fset = lambda self, value, k=key: setattr(self, "__" + k, value)
This is a classic Python pitfall. When you define
fget = lambda self: getattr(self, "__%s" % key)
the value of key is determined when fget is called, not when fget is defined. Since it is a nonlocal variable, its value is found in the enclosing scope of the __new__ function. By the time fget gets called, the for-loop has ended, so the last value of key is the value found. Python3's dict.item method returns items in a unpredictable order, so sometimes the last key is, say, __qualname__, which is why a suprising error is sometimes raised, and sometimes the same wrong value is returned for all attributes with no error.
When you define a function with a parameter with a default value, the default value is bound to the parameter at the time the function is defined.
Thus, the current values of key get corrected bound to fget and fset when you bind default values to k.
Unlike before, k is now a local variable. The default value is stored in fget.__defaults__ and fset.__defaults__.
Another option is to use a closure. You can define this outside of the metaclass:
def make_fget(key):
def fget(self):
return getattr(self, "__%s" % key)
return fget
def make_fset(key):
def fset(self, value):
setattr(self, "__" + key, value)
return fset
and use it inside the metaclass like this:
result_dct[key] = property(make_fget(key), make_fset(key))
Now when fget or fset is called, the proper value of key is found in the enclosing scope of make_fget or make_fset.
#unutbu's answer is perfectly fine and addressed the main caveats very well.
However, there is one more thing to note (I cannot comment yet so here I am posing an entire answer), note that classproperty's and instanceproperty's have different keys.
What you are doing here is entirely based on class properties. If one wishes to make a setter for an "instance" property the key must be f"_{clsname}__{key}". I lack the technical understanding of Python data model to explain why or if what I'm saying is entirely correct or has other caveats. Just posting this here as a side note.
This is especially important if you wish to allow the user to override the methods with custom ones like the example I provide here (I'm not sure even if it has no syntax error but still I post it here):
class MyMeta(type):
def __new__(cls, clsname, bases, info, **kwargs):
property_key = "__my_private" # should have been f"_{clsname}__my_private"
info[property_key] = "default_value"
if "my_getter" not in info:
info["my_getter"] = lambda self, key=property_key: getattr(self, key)
return super().__new__(cls, clsname, bases, info, **kwargs)
class MyClass(metaclass=MyMeta):
def my_getter(self):
return f"will fail to get {self.__my_private}"
MyClass().my_getter() # => Raises: AttributeError "_MyClass__my_private" not found.
# This would work so fine if no `self` keyword was being used (treated as classproperty)
I'm writing a python class that uses __setattr__ and __getattr__ to provide custom attribute access.
However, some attributes can't be handled in a generic way, so I was hoping to use descriptors for those.
A problem arises in that for a descriptor, the descriptor's __get__ will be invoked in favour of the instances __getattr__, but when assigning to an attribute, __setattr__ will be invoked in favour of the descriptors __set__.
An example:
class MyDesc(object):
def __init__(self):
self.val = None
def __get__(self, instance, owner):
print "MyDesc.__get__"
return self.val
def __set__(self, instance, value):
print "MyDesc.__set__"
self.val = value
class MyObj(object):
foo = MyDesc()
def __init__(self, bar):
object.__setattr__(self, 'names', dict(
bar=bar,
))
object.__setattr__(self, 'new_names', dict())
def __setattr__(self, name, value):
print "MyObj.__setattr__ for %s" % name
self.new_names[name] = value
def __getattr__(self, name):
print "MyObj.__getattr__ for %s" % name
if name in self.new_names:
return self.new_names[name]
if name in self.names:
return self.names[name]
raise AttributeError(name)
if __name__ == "__main__":
o = MyObj('bar-init')
o.bar = 'baz'
print o.bar
o.foo = 'quux'
print o.foo
prints:
MyObj.__setattr__ for bar
MyObj.__getattr__ for bar
baz
MyObj.__setattr__ for foo
MyDesc.__get__
None
The descriptor's __set__ is never called.
Since the __setattr__ definition isn't just overriding behaviour for a limited set of names, there's no clear place that it can defer to object.__setattr__
Is there a recommended way to have assigning to attributes use the descriptor, if available, and __setattr__ otherwise?
I think I'd approach this by having a mechanism to automatically mark which are the
descriptors in each class, and wrap the __setattr__ in a way that it'd call
object's normal behavior for those names.
This can be easily achieved with a metaclass (and a decorator for __setattr__
def setattr_deco(setattr_func):
def setattr_wrapper(self, attr, value):
if attr in self._descriptors:
return object.__setattr__(self, attr, value)
return setattr_func(self, attr, value)
return setattr_wrapper
class MiscSetattr(type):
def __new__(metacls, name, bases, dct):
descriptors = set()
for key, obj in dct.items():
if key == "__setattr__":
dct[key] = setattr_deco(obj)
elif hasattr(obj, "__get__"):
descriptors.add(key)
dct["_descriptors"] = descriptors
return type.__new__(metacls, name, bases, dct)
# and use MiscSetattr as metaclass for your classes
One of possible ways:
def __setattr__(self, name, value):
print "MyObj.__setattr__ for %s" % name
for cls in self.__class__.__mro__ + (self, ):
if name in cls.__dict__:
return object.__setattr__(self, name, value)
print 'New name', name, value
self.new_names[name] = value
It checks if name already defined in class, base classes or instance and then it calls object.__setattr__ which will execute descriptor __set__.
Another way:
def __setattr__(self, name, value):
print "MyObj.__setattr__ for %s" % name
try:
object.__getattribute__(self, name)
except AttributeError:
print 'New name', name, value
self.new_names[name] = value
else:
object.__setattr__(self, name, value)
But it will call descriptor's __get__.
P.S.
I'm not sure about need to check all __mro__ members since MyObj will contain inherited class members in __dict__.
Maybe for cls in (self.__class__, self):... will be enough.
I'm solving the python koans.
I haven't got any real problem until the 34th.
this is the problem:
Project: Create a Proxy Class
In this assignment, create a proxy class (one is started for you
below). You should be able to initialize the proxy object with any
object. Any attributes called on the proxy object should be forwarded
to the target object. As each attribute call is sent, the proxy
should record the name of the attribute sent.
The proxy class is started for you. You will need to add a method
missing handler and any other supporting methods. The specification
of the Proxy class is given in the AboutProxyObjectProject koan.
Note: This is a bit trickier that it's Ruby Koans counterpart, but you
can do it!
and this is my solution until now:
class Proxy(object):
def __init__(self, target_object):
self._count = {}
#initialize '_obj' attribute last. Trust me on this!
self._obj = target_object
def __setattr__(self, name, value):pass
def __getattr__(self, attr):
if attr in self._count:
self._count[attr]+=1
else:
self._count[attr]=1
return getattr(self._obj, attr)
def messages(self):
return self._count.keys()
def was_called(self, attr):
if attr in self._count:
return True
else: False
def number_of_times_called(self, attr):
if attr in self._count:
return self._count[attr]
else: return False
It works until this test:
def test_proxy_records_messages_sent_to_tv(self):
tv = Proxy(Television())
tv.power()
tv.channel = 10
self.assertEqual(['power', 'channel='], tv.messages())
where tv.messages() is ['power'] because tv.channel=10 is taken by the proxy object and not the television object.
I've tried to manipulate the __setattr__ method, but I always end in a unlimited loop.
edit 1:
I'm trying this:
def __setattr__(self, name, value):
if hasattr(self, name):
object.__setattr__(self,name,value)
else:
object.__setattr__(self._obj, name, value)
But then I get this error in a loop on the last entry:
RuntimeError: maximum recursion depth exceeded while calling a Python object
File "/home/kurojishi/programmi/python_koans/python 2/koans/about_proxy_object_project.py", line 60, in test_proxy_method_returns_wrapped_object
tv = Proxy(Television())
File "/home/kurojishi/programmi/python_koans/python 2/koans/about_proxy_object_project.py", line 25, in __init__
self._count = {}
File "/home/kurojishi/programmi/python_koans/python 2/koans/about_proxy_object_project.py", line 33, in __setattr__
object.__setattr__(self._obj, name, value)
File "/home/kurojishi/programmi/python_koans/python 2/koans/about_proxy_object_project.py", line 36, in __getattr__
if attr in self._count:
The loop is in __getattr__.
You are using hasattr in __setattr__ to decide whether you should write to the local or proxied object. This works well for all but one case.
In your __init__ you have the following line:
self._count = {}
This calls __setattr__ with '_count' which does not exist at that point and therefore (hence hasattr returns False) is forwarded to the proxied object.
If you want to use your approach you have to write your __init__ like this:
def __init__(self, target_object):
object.__setattr__(self, '_count', {})
#initialize '_obj' attribute last. Trust me on this!
object.__setattr__(self, '_obj', target_object)
As I understand maybe your problem is related with the recursive call when you set and attribute value. From docs:
If __setattr__() wants to assign to an instance attribute, it should not simply execute "self.name = value" -- this would cause a recursive call to itself. Instead, it should insert the value in the dictionary of instance attributes, e.g., "self.__dict__[name] = value". For new-style classes, rather than accessing the instance dictionary, it should call the base class method with the same name, for example, "object.__setattr__(self, name, value)".
setattr is called on all assignments. It's more like getattribute than getattr. This also affects code in the __init__ method.
This means that the first branch of this code will almost always fail, only attributes inherited from object will pass the test:
def __setattr__(self, name, value):
if hasattr(self, name):
object.__setattr__(self,name,value)
else:
object.__setattr__(self._obj, name, value)
Instead we
can assume that assignments are meant for the Proxy unless it has an _obj attribute. Hence the comment in __init__. We set up our proxy's attributes, then add the target object and all future assignments get sent to it.
def __setattr__(self, name, value):
if hasattr(self, '_obj'):
object.__setattr__(self._obj, name, value)
else:
object.__setattr__(self, name, value)
But by using hasattr we would also need to alter __getattr__ to check for _obj to prevent recursion:
def __getattr__(self, name):
if '_obj' == name:
raise AttributeError
if attr in self._count:
self._count[attr]+=1
else:
self._count[attr]=1
return getattr(self._obj, attr)
An alternative would be to inspect the proxy's __dict__ attribute directly in the __setattr__ method:
def __setattr__(self, name, value):
if '_obj' in self.__dict__:
...
from the test, it is a requirement for proxy to log all the attribute calls via proxy. And the proxy has only few built-in methods which are exceptionally used for logging, so my answer was:
class Proxy(object):
def __init__(self, target_object):
self.logs=[]
self._obj = target_object
def __getattribute__(self, attrname):
if attrname in ['_obj','logs','messages','was_called','number_of_times_called'] :
return object.__getattribute__(self, attrname)
else:
self.logs.append(attrname)
return object.__getattribute__((object.__getattribute__(self, '_obj')), attrname)
def __setattr__(self, name, value):
if hasattr(self, '_obj'):
self.logs.append(name)
object.__setattr__(object.__getattribute__(self,'_obj'), name, value)
else :
object.__setattr__(self, name, value)
After this it is quite easy to implement other methods ('messages', 'was_called', ... )
Sorry for necro'ing old question.
and I found out that getattribute can be changed : just check whether the attribute is in the target object.
def __getattribute__(self, attrname):
if attrname not in dir(object.__getattribute__(self, '_obj')):
return object.__getattribute__(self, attrname)
else:
self.logs.append(attrname)
return object.__getattribute__((object.__getattribute__(self, '_obj')), attrname)
class Proxy(object):
"""Proxy class wraps any other class, and adds functionality to remember and report all messages called.
Limitations include that proxy blocks all direct subclass calls to:
messages, number_of_times_called, was_called, _obj, and _message_counts.
These calls must be made directly like my_proxy_instance._obj.messages.
"""
def __init__(self, target_object):
print 'initializing a proxy for ' + target_object.__class__.__name__
# WRITE CODE HERE
self._message_counts = Counter();
#initialize '_obj' attribute last. Trust me on this!
self._obj = target_object
# WRITE CODE HERE
def __getattr__(self, attr_name):
print 'getting an attribute: "' + attr_name + '" from "' + self._obj.__class__.__name__ + '"'
self._message_counts[attr_name] += 1
print self._message_counts
return object.__getattribute__(self._obj, attr_name)
#def __getattribute__(self, attr_name):
# print "intercepted!~ " + attr_name
# object.__getattribute__(self, attr_name)
def __setattr__(self, attr_name, value):
if((attr_name == '_obj') | (attr_name == '_message_counts')): # special proxy attributes.
print 'setting the PROXY attribute: "' + attr_name + '"'
object.__setattr__(self, attr_name, value)
else:
print 'setting the REAL attribute: "' + attr_name + '"'
self._message_counts[attr_name+"="] += 1
object.__setattr__(self._obj, attr_name, value)
def messages(self):
return self._message_counts.keys()
def number_of_times_called(self, attr_name):
return self._message_counts[attr_name]
def was_called(self, attr_name):
return attr_name in self._message_counts
What I did was take all the calls to attributes in the proxy and call them via object.__getattribute__ to avoid recursion.
That did not work for methods so I wrapped the method calls in a try..except AttributeError to try them first in the proxy. and then if they raise an error try them in the child object.
If anyone has a more elegant solution would love to see it.
from runner.koan import *
from collections import Counter
class Proxy(object):
def __init__(self, target_object):
self._messages=[]
self._obj = target_object
def messages(self):
return self._messages
def was_called(self, message):
return message in self._messages
def number_of_times_called(self, message):
_count = Counter(self._messages).get(message)
if _count:
return _count
else: # catch None
return 0
def __getattribute__(self, attr_name):
try: # call on self
retval = object.__getattribute__(self, attr_name)
except AttributeError: # call on child object
retval = self._obj.__getattribute__(attr_name)
object.__getattribute__(self, '_messages').append(attr_name)
return retval
def __setattr__(self, attr_name, attr_value):
if hasattr(self, '_obj'): # call child object and log message
self._obj.__setattr__(attr_name, attr_value)
attr_name += "="
object.__getattribute__(self, '_messages').append(attr_name)
else: # use this before_obj is set in __init__
object.__setattr__(self, attr_name, attr_value)
def messages(self):
return self._messages
why not use method_missing?
my answer:
class Proxy
def initialize(target_object)
#object = target_object
# ADD MORE CODE HERE
#messages = []
end
# WRITE CODE HERE
def method_missing(method_name, *args, &block)
#messages.push method_name unless method_name == :messages
#object.send method_name, *args, &block
end
def messages
#messages
end
def called? target
#messages.include? target
end
def number_of_times_called target
result = 0
#messages.each do |t|
result += 1 if t == target
end
result
end
end