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What are metaclasses in Python?
...ass is an instance of a metaclass.
While in Python you can use arbitrary callables for metaclasses (like Jerub shows), the better approach is to make it an actual class itself. type is the usual metaclass in Python. type is itself a class, and it is its own type. You won't be able to recreate somet...
Django: Get list of model fields?
...s which (ultimately) inherits from models.Model . I want to get a list of all the fields defined for this model. For example, phone_number = CharField(max_length=20) . Basically, I want to retrieve anything that inherits from the Field class.
...
Difference between a theta join, equijoin and natural join
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A theta join allows for arbitrary comparison relationships (such as ≥).
An equijoin is a theta join using the equality operator.
A natural join is an equijoin on attributes that have the same name in each relationship.
Additionally,...
What do all of Scala's symbolic operators mean?
...se of teaching, into four categories:
Keywords/reserved symbols
Automatically imported methods
Common methods
Syntactic sugars/composition
It is fortunate, then, that most categories are represented in the question:
-> // Automatically imported method
||= // Syntactic sugar
++= // Syn...
What is the difference between public, protected, package-private and private in Java?
...e MyClass and I'm doing AnotherClass extends MyClass I will have access to all protected and public methods and properties from within AnotherClass. If I do MyClass myClass = new MyClass(); in AnotherClass somewhere - let's say the constructor - I will only have access to the public methods if it is...
How to set the prototype of a JavaScript object that has already been instantiated?
...n set of rules. This is currently unresolved but at least it will be officially part of JavaScript's specification.
This question is a lot more complicated than it seems on the surface, and beyond most peoples' pay grade in regards to knowledge of Javascript internals.
The prototype property of an...
How to select a single field for all documents in a MongoDB collection?
... include several fields. In the following operation, find() method returns all documents that match the query. In the result set, only the item and qty fields and, by default, the _id field return in the matching documents.
db.inventory.find( { type: 'food' }, { item: 1, qty: 1 } )
In this example ...
How to get the parents of a Python class?
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If you want all the ancestors rather than just the immediate ones, use inspect.getmro:
import inspect
print inspect.getmro(cls)
Usefully, this gives you all ancestor classes in the "method resolution order" -- i.e. the order in which ...
How to create the most compact mapping n → isprime(n) up to a limit N?
Naturally, for bool isprime(number) there would be a data structure I could query.
I define the best algorithm , to be the algorithm that produces a data structure with lowest memory consumption for the range (1, N], where N is a constant.
Just an example of what I am looking for: I could rep...
How can I recover the return value of a function passed to multiprocessing.Process?
... need to know which process is returning which value. If that what you actually need to know about the process, or do you need to correlate between your list of inputs and the list of outputs? In that case, I would recommend using multiprocessing.Pool.map to process your list of work items.
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