In object-oriented programming, a metaclass is a class whose instances are classes. Just as an ordinary class defines the behavior of certain objects, a metaclass defines the behavior of certain classes and their instances. Not all object-oriented programming languages support metaclasses.
Questions tagged [metaclass]
1179 questions
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votes
1 answer
Magic methods on class self
I am looking for a way to call magic methods on class instances. In my case, I want to call hash on class based on properties. I found solution with metaclass, but I cannot access class properties from metaclass's method.
class X(type):
…
Patrik Valkovič
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- 7
- 26
-1
votes
1 answer
Metaclasses and methods
Adding a method to metaclass works perfectly in the below example.
class Test(object):
def __init__(self, x):
self.x = x
def double(self):
return self.x*2
# method to add
def quadruple(self):
return self.x*4
#…
David Ross
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votes
2 answers
__metaclass__ not worked when create class with type("Test", (Base,), {'__metaclass__':Meta, ...})
cls = type("Test", (Base,), {"__metaclass__": Meta, "a": 1, ...})
I want to make some check for the attrs in the 3rd argument with Meta class, but this seem not worked, is there any other method?
wartalker
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votes
1 answer
Implement _del_ method for a class with __getattribute__ overriden
Taking this question as a pointer, let's say there exists a class like the following:
class Container(object):
def __init__(self, **kwargs):
self._meta = defaultdict(lambda: None)
for attr, value in kwargs.iteritems():
…
viksit
- 7,542
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votes
1 answer
How does python create class using attributes in the parameter list of __new__() function?
I want to know how the __new__ function of type works, how can it create a class using the attr parameters.
for Example:
class ModelMetaclass(type):
def __new__(cls, name, bases, attrs):
return type.__new__(cls, name, bases,…
赵鹏程
- 1
-1
votes
1 answer
GroovyCastException metaclass i18n
This question is connected with another.
I'd like to add properties to constructor and overwrite getLocalisedMessage() function to get proper translated message with error. First I want to overload constructor to set properties, but when I…
Michal_Szulc
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votes
1 answer
practical example of defining using metaclass like setting it to ABCMeta or LoggingType
Example of setting metaclass to LoggingType i spotted at my workplace.
import logging as _logging
class SomeClass(object):
__metaclass__ = _logging.LoggingType
Here is the example I have seen for ABCMeta set to __metaclass__
I want to know the…
Ciasto piekarz
- 7,853
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-1
votes
1 answer
How to build a hierarchical view of inherited classes in Python?
This is a question I tried to avoid several times, but I finally couldn't escape the subject on a recent project. I tried various solutions and decided to use one of them and would like to share it with you. Many solutions on internet simply don't…
dcexcal
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votes
1 answer
How to define dynamically, that some method of a class already exists in its base class? (Python 2.7)
I need to define either some method of a ChildClass overrides already existing method in BaseClass.
(Python 2.7)
class BaseClass(object):
def method(self):
pass
class ChildClass1(BaseClass):
def method(self):
pass
class…
efi
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votes
1 answer
Objective-C dynamically define a method at runtime via a string
After reading several blog posts and searched through SO, I know how to add a method to a class, but no one touches on how to define the method body from a String.
Here's an example blog post that gets close to what I want to…
maximus
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- 56
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votes
2 answers
How to delete a class from globals right after creation?
I have a metaclass that just append a prefix to the classes on my modules. So far so good, the problem is that I want to remove the definition of the class that is calling the metaclass. For example if class A is prefixed to PrefixA I will end with…
Alvaro Fuentes
- 16,937
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votes
1 answer
How can the shape of a pytables table column be defined by a variable?
I'm trying to create an IsDescription subclass, so that I can define the structure of a table I'm trying to create. One of the attributes of the subclass** needs to be shaped given a certain length that is unknown until runtime (it depends on a file…
darthbith
- 18,484
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-1
votes
1 answer
type function on class with metaclass
class ParamMeta(type):
def __str__(self):
return self.__name__
class Param(object):
__metaclass__=ParamMeta
class SomeParam(Param):
pass
What I want is for:
type(SomeParam)==Param
How do I achieve this?
Update: what do I need to…
jldupont
- 93,734
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votes
1 answer
How to implement MVC like this in Python?
For example, I have a config file named rule1.conf like this:
[Basis]
user = "sunhf"
time = "2012-12-31"
[Bowtie]
path = "/usr/bin/bowtie"
index = "/mnt/Storage/sync/hg19"
And a models.py like this(using a package named magic.py..):
from magic…
Hanfei Sun
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votes
1 answer
Why do I get an Error when creating an instanz of a class that has a metaclass
class Meta(type):
def __new__(cls, class_name, bases, attrs):
a={}
for name, val in attrs.items():
if name.startswith("__"):
a[name] = val
else:
a[name.upper()] = val
…
Fuorb
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