descriptor

问题 I am learning about descriptors in python. I want to write a non-data descriptor but the class having the descriptor as its classmethod doesn't call the __get__ special method when I call the classmethod. This is my example (without the __set__ ): class D(object): "The Descriptor" def __init__(self, x = 1395): self.x = x def __get__(self, instance, owner): print "getting", self.x return self.x class C(object): d = D() def __init__(self, d): self.d = d And here is how I call it: >>> c = C(4) >

问题 I am learning about descriptors in python. I want to write a non-data descriptor but the class having the descriptor as its classmethod doesn't call the __get__ special method when I call the classmethod. This is my example (without the __set__ ): class D(object): "The Descriptor" def __init__(self, x = 1395): self.x = x def __get__(self, instance, owner): print "getting", self.x return self.x class C(object): d = D() def __init__(self, d): self.d = d And here is how I call it: >>> c = C(4) >

问题 I am new to Python and looking through its documentation I encountered the following example of the descriptor protocol that in my opinion is incorrect. . It looks like class IntField: def __get__(self, instance, owner): return instance.__dict__[self.name] def __set__(self, instance, value): if not isinstance(value, int): raise ValueError(f'expecting integer in {self.name}') instance.__dict__[self.name] = value # this is the new initializer: def __set_name__(self, owner, name): self.name =

问题 I have about 20 methods to redirect to a wrapper method that takes the original method, and the rest of the arguments: class my_socket(parent): def _in(self, method, *args, **kwargs): # do funky stuff def recv(self, *args, **kwargs): return self._in(super().recv, *args, **kwargs) def recv_into(self, *args, **kwargs): return self._in(super().recv_into, *args, **kwargs) # and so on... How can I add more of these methods programmatically? This is about as far as I get before everything starts to

问题 Or does the attribute have to be defined outside of any class methods? So my descriptor object is this. The IDN object already has some information about the UserNameField, so I want to use it. class UserNameElement(basePageElement): _testMethodName="UserNameElement Test method" def __init__(self, IDN, PTF): print "creating UserNameElement" self.locator = IDN.UserNameField() And here is my calling class. Where I want to instantiate the UserNameElement object class LoginPageObject

问题 please i like to classify a set of image in 4 class with SIFT DESCRIPTOR and SVM. Now, using SIFT extractor I get keypoints of different sizes exemple img1 have 100 keypoints img2 have 55 keypoints.... how build histograms that give fixed size vectors with matlab 回答1: In this case, perhaps dense sift is a good choice. There are two main stages: Stage 1 : Creating a codebook. Divide the input image into a set of sub-images. Apply sift on each sub-image. Each key point will have 128 dimensional

问题 The python 3.3 documentation tells me that direct access to a property descriptor should be possible, although I'm skeptical of its syntax x.__get__(a) . But the example that I constructed below fails. Am I missing something? class MyDescriptor(object): """Descriptor""" def __get__(self, instance, owner): print "hello" return 42 class Owner(object): x = MyDescriptor() def do_direct_access(self): self.x.__get__(self) if __name__ == '__main__': my_instance = Owner() print my_instance.x my

问题 I would like to create a class that behaves as a python variable but calls some callback function when the "variable" is changed/read. In other words, I'd like to be able to use the class as follows: x=myClass(change_callback, read_callback) defines x as an instance of myclass. The constructor ( INIT ) takes 2 functions as paramater: a function to be called each time x is changed, and a function to be called each time x is "read" The following statement: x=1 would "save" 1 and trigger a call

问题 I'm trying my hand at making an Object-Oriented text-based game in Python, and attempting to implement my first properties and decorators. Using the chapter 5 in the book 'Python 3 Object Oriented Programming', I've tried to use the examples and concepts discussed to get the following code to set a Game-object's 'current_room' property upon instantiation: class Room(object): ''' An area of the game's map.''' def __init__(self): print("Accessing the Room __init__ method.") class FirstRoom(Room

问题 (and if not, is there an approach that accomplishes a similar thing?) For example, here's an example of a "bound" descriptor: class VerboseDescriptor(object): def __init__(self, init): self.val = init def __get__(self, obj, typ=None): print("[%s] Get is %s" % (obj, self.val)) return self.val def __set__(self, obj, val): print("[%s] Set to %s" % (obj, val)) self.val = val class Holder(object): def __init__(self, name): self.name = name def __repr__(self): return "Holder(%s)" % self.name val =