I have to run a method (named "top") at several objects. So the reference to the object is a parameter of "top". Inside "top" I call a method "down" of the object. Of course this works. But as Visual Studio Code does not know, if the objects selected by the parameter have a method named "down", it cannot highlight the method name "down" at the line where it is called (in my environment the string "down" of "ref.down()", see example code, stays white instead of getting yellow). So my questions are: Am I working in a wrong way? Is there any better style of programming, which enables Visual Studio Code to highlight always any existing method?
This is my example python code:
class myclass_top:
def __init__(self):
ref1 = myclass_bottom()
ref2 = myclass_bottom()
self.top(ref1)
self.top(ref2)
def top(self, ref):
ref.down() # <---- The string "down" is not highlighted.
class myclass_bottom:
def __init__(self):
self.var = 0
def down(self):
self.var -= 1
Related
I'm trying to create a class that only creates an instance if the arguments passed in during instantiation are a unique combination. If the combination of arguments have previously been passed in, then return the instance that has already been previously created.
I'd like for this class to be inherited by other classes so they inherit the same behavior. This is my first attempt at a solution,
The base/parent class to be inherited:
class RegistryType(type):
def __init__(cls, name, bases, namespace, *args):
cls.instantiated_objects = {}
class AdwordsObject(object, metaclass=RegistryType):
api = AdWordsAPI()
def __new__(cls, *args):
object_name = '-'.join(args)
if object_name in cls.instantiated_objects:
return cls.instantiated_objects[object_name]
else:
obj = super(AdwordsObject, cls).__new__(cls)
cls.instantiated_objects[object_name] = obj
# cls.newt_connection.commit()
return obj
And this is how it's being used in the child class:
class ProductAdGroup(AdwordsObject):
# init method only called if object being instantiated hasn't already been instantiated
def __init__(self, product_name, keyword_group):
self.name = '-'.join([product_name, keyword_group])
#classmethod
def from_string(cls, name: str):
arguments = name.split('-')
assert len(arguments) == 2, 'Incorrect ad group name convention. ' \
'Use: Product-KeywordGroup'
ad_group = cls(*arguments)
return ad_group
I've ran the program with this setup but it seems like a new dict is being created every time ProductAdGroup() is being created so the memory is exploding... even though the program returns the instance that had already been previously instantiated.
Is there anyway to fix this?
Thanks!!!
Your code seems to be right - the only thing incorrect above is that your __init__ method will always be called when instantiating a new class, regardless of a previous instance being returned by __new__ or not.
So, if you create extra objects in your __init__ method, that may be the cause of your memory leak - however, if you bind these new objects to the instane (self), they shuld just override a previously created object in the same place - which would them be freed. . In the code posted here, that happens with self.name- it may be that your real __init__ does more things, and associate new objects to other places than the instance (like, apending them to a list). If your __init__ methods are just as shown the cause for your memory growing is not evident in the code you supply.
As an extra advice, but not related to the problem you relate, I add that you don't need a metaclass for this at all.
Just check for the existence of an cls.instantiated_objects dict in the __new__ method itself. Not writting an unneeded metaclass will simplify your codebase, avoid metaclass conflicts if your class hierarchy evolves, and may even do away with your problem if there is more code on your metaclass than you are showing here.
The base class __new__ method can be rewritten something like this:
class AdwordsObject(object):
def __new__(cls, *args):
if not cls.__dict__.get("instantiated_objects"):
cls.instantiated_objects = {}
name = '-'.join(args)
if name in cls.instantiated_objects:
return cls.instantiated_objects[name]
instance = super().__new__(cls)
cls.instantiated_objects[name] = instance
return instance
And there is no more need for a custom metaclass.
I'm facing a problem and studying the OCaml documentation did not enable me to find a satisfying solution yet.
The following snippet illustrates my problem:
class A = object (self)
(* this should not be overwrittable in subclass B, but callable
on objects of type B!
*)
method dangerous_one input =
(do dangerous stuff...)
let safe_output = safe_dangerous_one input in
(... more dangerous things done with safe_output ...)
(* This is safe, should be overwrittable and callable in subclass *)
method safe_dangerous_one input = (...)
end
class B = object(self) inherit A as super
method! safe_dangerous_one input = (* subclass behaviour ... *)
end
To sum up the snippet: class A is base class to subclass B.
It has a dangerous method that is complex and has some dark corners I don't want client code to have to deal with.
In fact, I want to prohibit subclasses from overwriting method "dangerous_one".
Instead, they should overwrite the function "safe_dangerous_one".
Furthermore, it should be possible to CALL "b#dangerous_one" where "b : B" which uses the (new) definition of the "safe_dangerous"-parts as specified in class B.
My dilemma appears to be: if I simply make method "dangerous_one" private, nothing keeps the client code in class B from overwriting it, potentially even making it public.
If I hide its implementation from the signature, it can not be overwritten anymore, but I cannot call "b#dangerous_one" anymore - the code becomes inaccessible to calls also.
Is there any way to achieve what I aim to do?
Best,
Nablezen
If I hide its implementation from the signature, it can not be overwritten anymore, but I cannot call "b#dangerous_one" anymore - the code becomes inaccessible to calls also.
You can, you just need to make it private, you can't hide public methods:
class type safe = object
method safe_dangerous_one : in_channel -> int
end
class a : safe = object (self)
method private dangerous_one input = input_binary_int input
method safe_dangerous_one input =
max 255 (self#dangerous_one input)
end
class b parameters = object(self)
inherit a parameters as super
method! safe_dangerous_one input =
super#safe_dangerous_one input + 1
end
If you want unsafe method to be accessible, but not overridable, then just re-publish it at another name (kind of NVI):
class type safe = object
method unsafe_dangerous_one : in_channel -> int
method safe_dangerous_one : in_channel -> int
end
class a : safe = object (self)
method private dangerous_one input = input_binary_int input
method unsafe_dangerous_one input = self#dangerous_one input
method safe_dangerous_one input =
max 255 (self#dangerous_one input)
end
class b = object(self)
inherit a as super
method! safe_dangerous_one input =
super#safe_dangerous_one input + 1
end
And a piece of free advice. In other languages, classes and methods are used as a tool for structuring programs, because they have no better tools. In OCaml you have first class functions, records, structures, etc. So it is better to use a proper tool for at each situation. When you design a class, you should understand, that the method by its original definition (not spoiled by C++/Java/Python/etc) is something overridable. A method is an operation that has an implementation that varies across some genera. So, if you define something as a method, and then trying hard to prevent people from overriding it, then chances are high that you're doing something wrong. If you don't want it to be overridable, then just don't define it as a method at all. In your case you should put dangerous_one operation into a let-bound function. You can bound it in the context of the class, so that you will have an access to all parameters, or you can bind it on a toplevel, the choice is yours:
class a parameters =
let dangerous_one input = input_binary_int input in
object (self)
method safe_dangerous_one input =
max 255 (dangerous_one input)
end
class b = object(self)
inherit a as super
method! safe_dangerous_one input =
super#safe_dangerous_one input + 1
end
Also, a very good source of documentation about OCaml class system is Jason Hickey's Introduction to Objective Caml. It is slightly outdated, but is still very good.
The behaviour can be observed by placing this code in a playground:
import Foundation
import ObjectiveC
class TestClass {}
var obj = TestClass()
let stringValue = "xyz"
let key = "def"
objc_setAssociatedObject(obj, key, stringValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
//let f = "f"
let returnedString = objc_getAssociatedObject(obj, key)
This works and returns "xyz" from the objc_getAssociatedObject call.
However, if you remove the comment from the let f = "f" line. The objc_getAssociatedObject call now returns nil.
I'm baffled as to how setting a totally unrelated variable can effect the call.
Any ideas?
Looks like a bug.
The objc_... methods are part of the Objective-C runtime. They shouldn't exist in Swift.
That said they clearly do. So my guess is that there's something happening when you set that method that kicks the runtime, similar to calling synchronize on NSUserDefaults.
Edit: This NSHipster article explains that the ObjC runtime is actually there.
Edit 2: I tried a few experiments, and I'll make your question even weirder. Wrapping the test case inside the object yields the same result. But changing the variable name to an underscore fixes the problem:
let _ = "f"
I bet assigning a variable overwrites whatever runtime associations you set manually. The underscore just tells the compiler that you aren't using the result of the assignment.
I have a question regarding the traitsui tutorial by Gael Varoquaux.
In code snippet 7 he makes a CaptureThread class for producing a thread for taking images from a camera. He also make a Camera class.
class TextDisplay(HasTraits):
string = String()
view = View(Item('string', show_label=False, springy=True, style='custom'))
class CaptureThread(Thread):
def run(self):
#self.display is set outside the class definition by the caller
self.display.string = 'Camera started\n' + self.display.string
n_img = 0
while not self.wants_abort:
sleep(0.5)
n_img += 1
self.display.string = ' %d image captured\n' % n_img \
+ self.display.string
self.display.string = 'Camera stopped\n' + self.display.string
class Camera(HasTraits):
start_stop_capture = Button()
display = Instance(TextDisplay)
capture_thread = Instance(CaptureThread)
view = View( Item('start_stop_capture', show_label=False))
def _start_stop_capture_fired(self):
if self.capture_thread and self.capture_thread.isAlive():
self.capture_thread.wants_abort = True
else:
self.capture_thread = CaptureThread()
self.capture_thread.wants_abort = False
self.capture_thread.display = self.display
self.capture_thread.start()
I have two questions about this code:
1) Why in the Camera class definition does he make capture_thread a Trait, by calling Instance(CaptureThread)? CaptureThread is just a thread class, why should we make a trait instance out of it?
2) In the CaptureThread class he makes use of a field self.display.string and of self.wants_abort. These two fields are not passed in via a constructor method, rather they are assigned outside of the class definition by the Camera class. Is this the best practise? Since if the user of the CaptureThread forgot to set these two fields, then an error would occur. Are there some sensible guidelines to know when I can assign thing like that, or I should use a constructor to assign them?
I hope that these questions make sense, and that this is the right place to ask them!
Thanks, labjunky
capture_thread = Instance(CaptureThread) doesn't make an instance of CaptureThread. It is more of a declaration that gets consumed by the Camera class when the class gets created. It tells that Camera class that it will have an attribute named capture_thread that should be an instance of CaptureThread or None and will default to None. This default lets the "test if self.capture_thread is initialized, otherwise create it" logic in _start_stop_capture_fired() a little cleaner, at least to some people's tastes.
For threading.Thread subclasses, yes, it's one idiomatic way to do it, though not the only one. Thread already has a specific __init__ implementation, and you could override it to do something else, but it is understandable that the author would avoid doing so in this case.
This is not the idiomatic way to initialize HasTraits subclasses which is indeed to use keyword arguments.
I ran into a problem using java objects in jython today because jython is trying to be intelligent and automatically creates properties for (simple) getter/setter methods - For each method a field with the leading get/set removed and the next letter converted to lowercase is created:
//java code
class MyClass {
public List<Thing> getAllThings() { ... }
public List<Thing> getSpecificThings(String filter) { ... }
public void setSomeThing(SomeThing x) { ... }
[...]
}
#jython code
obj = MyClass()
hasattr(obj, "allThings") #-> True
hasattr(obj, "specificThings") #-> False because getSpecificThings has a param
hasattr(obj, "someThing") #-> False BUT
"someThing" in dir(obj) #-> True
The last line summarizes my problem here - the result of dir contains these fields (even when executed on obj.class instead of obj). I need a list of all methods callable on the object, which for my objects basically is the result of dir without these properties and filtered to exclude everything inherited from java.lang.Object and things starting with an underscore (the purpose of this is to automagically convert some python classes to java equivalents, e.g. dicts to Maps). In theory I could use __dict__ which doesn't contain them, but this would mean I'd have to recursively evaluate the base classes' __dict__s too, which I would like to avoid. What I am currently doing is seeing if the attribute actually exists and then check if it has an argslist attribute (meaning it is a method), which is true for every dir entry except for the generated properties:
for entry in dir(obj):
#skip things starting with an underscore or inherited from Object
if entry.startswith("_") or entry in dir(java.lang.Object): continue
#check if the dir entry is a fake setter property
if not hasattr(obj, entry): continue
#check if the dir entry has an argslist attribute (false for getter props)
e = getattr(obj, entry)
if not hasattr(e, "argslist"): continue
#start actual processing of the entry...
The problem with this approach is that the objects in question are interfaces to beans and a getSomething method typically fetches data from a database, so the getattr call for a property makes a roundtrip to the DB which can take multiple seconds and waste tons of memory.
Can I stop jython from generating these properties? If not, does anybody have an idea how I can filter out the properties without accessing them first? The only thing I could think of was checking if dir contains a method named get/set<property>, but this seems hackish and could generate false positives, which must be avoided.
The answer was easier than anticipated. While a hasattr of the property is True for an object instance, it is False for the objects class if the get-method in question is not static - the class doesn't have the property as you can't execute the method on it. The updated loop now looks like this:
for entry in dir(obj):
#skip things starting with an underscore or inherited from Object
if entry.startswith("_") or entry in dir(java.lang.Object): continue
#check if the dir entry is a fake property
if not hasattr(obj.class, entry): continue
#check if the dir entry has an argslist attribute (false if not a method)
e = getattr(obj, entry)
if not hasattr(e, "argslist"): continue
#start actual processing of the entry...