Difficulty understanding the Python data model and how built-in functions are mapped to special methods

I have Java training and I study the Python data model. More specifically, I'm curious to know how and when special methods (e.g. __add__) call themselves.

It seems that the Python interpreter can execute these special methods when it encounters some built-in functions. To take an example from the book "Fluent Python", if you have a class like the following FrenchDeck

import collections

Card = collections.namedtuple('Card', ('rank', 'suit'))

class FrenchDeck:
    ranks = (str(n) for n in range(2, 11)) + list('JQKA')
    suits = 'spades diamonds clubs hearts'.split()

    def __init__(self):
        self._cards = (Card(rank, suit) for suit in self.suits
                                        for rank in self.ranks)

    def __len__(self):
        return len(self._cards)

    def __getitem__(self, position):
        return self._cards(position)

then __getitem__ will be called when the Python interpreter encounters things like for card in FrenchDeck() or FrenchDeck()(11).

It seems expressive but also extremely vague. How can I determine which built-in functions call my special methods? There seems to be an implicit mention of mappings between built-in and special methods in the instructions in the Python Data Model section like

It is recommended that mappings and sequences implement the __contains__() to allow efficient use of the in operator.

But I can't find a clear reference document with instructions like "for user-defined classes, in use __contains__ if it exists, otherwise it will use __getitem__".

fuzzy linear advection equation by finite difference methods

I need to write an acode to solve the advection equation in a D, I need a unique parametric. how can i do this using finite difference methods such as upwind and leapfrog?

python – Why do some pandas methods have inplace = True while others do not?

When working with pandas, I find that some methods have inplace=True For example.

df.drop(columns=("first", "last"), inplace=True)

While some methods do not have this argument and we have to explicitly assign it to a variable.

df = df.append(df2, ignore_index=True)

Is there a specific reason behind this?
Can't we just have a uniform way of ensuring that the argument is present for all methods of pandas? (as it removes the hassle of assigning it to another variable).

Any help is appreciated. Thank you.

factory – Static factories and methods

So almost all of the posts I have read on oop by purists, they continue to point out that the use of static methods is anti-pattern and breaks testability of the code.
On the other hand, whenever I look for a sample code using factories (whatever the programming language) specifically for object building purposes, I see a static method in the d & # 39; class. Factory returning the constructed object. (pseudo code below)

class ProductFactory() {

    public static function make(string name): Product
    {
        if(name contains TV)
            return new TVProduct(name)
        else 
            return new HomeAppliance(name);
    }
}

product = ProductFactory->make('LCD TV');

To me, that sounds perfectly fine because, ultimately, I want an instance of the object and not the factory instance as will be the case below.

productFactory = new ProductFactory();
product = productFactory->make('LCD TV');

My question is twofold here.

1- What is the real way to use the factories? is the static method in a factory the appropriate and accepted way to use them?

2- How to write unit tests for a factory that uses a static method?

I hope that my understanding of the use of factories for the construction of objects is not fundamentally flawed.

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I hope it helps.

python – Mocking pathlib.Path I / O methods in a maintainable way that tests functionality, not implementation

I have a function that builds a path based on an input function and creates the parent directory.

When writing a unit test for this function, I want to make fun of the I / O part of the function, namely .exists() and .mkdir() methods of pathlib.Path objects. However, since the two are not called until the path is built, I find myself rebuilding the implementation using a long chain of return_value.__truediv__ access, as below:

import pathlib
import unittest.mock
import datetime


def get(b, t, c):
    b = pathlib.Path(b)
    p = b / "tofu" / t.strftime("%Y%m%d") / f"{c:>02d}"https://codereview.stackexchange.com/"quinoa.txt"
    if p.exists():
        print(p, "exists")
    else:
        p.parent.mkdir(exist_ok=True, parents=True)
    return p



@unittest.mock.patch("pathlib.Path", autospec=True)
def test_get(pP):
    pP.return_value.__truediv__.return_value.__truediv__.return_value.
                    __truediv__.return_value.__truediv__.return_value.
                    exists.return_value = False
    get("quorn", datetime.datetime.now(), 42)
    pP.return_value.__truediv__.return_value.__truediv__.return_value.
                    __truediv__.return_value.__truediv__.return_value.
                    parent.mkdir.assert_called_once()

This test is successful, but I have several concerns:

  • It tests the implementation rather than the functionality. If I were to rewrite the second line get read p = b / t.strftime("tofu%Y%m%d") / f{c:>02d} / "quinoa.txt", the functionality would be the same, but the test would fail because I would no longer make fun of the good value.
  • It is difficult to read and easy to misjudge the depth of __truediv__.return_value chain.

In addition to moving I / O out of get, can I make fun of this in another way, who doesn't share these limitations? Or does the difficulty of writing a good test (with model) tell me that my function is too complex, despite its small size?

Unity – Unity2D: child class inheriting from onCollisionEnter () methods

I may be an idiot to ask this, but I can't seem to solve it myself, I have a GenericWeapon class which has an onCollisionEnter () method which I want to apply to all child classes who inherit it, here is the code:

public void onCollisionEnter(Collider target){
    Debug.Log("Collided with player!");
    if(target.GetComponent()){
        bc2d.enabled = false;
        rb2d.Sleep();
        equip(target.GetComponent());
    }
}

My child class is as follows:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class RangedWeapon : GenericWeapon
{
    // Start is called before the first frame update
    void Start()
    {
    }
    // Update is called once per frame
    void Update()
    { 
    }
    public void attack(){
    }
}

and my in GameObject has the RangedWeapon class as a component but the GameObject does not seem to detect collisions with the player. Could anyone tell where i am wrong?

python – What methods to predict the location of future crime scenes based on previous locations?

I know it's silly that such a small amount of functionality but, to learn more about geospatial prediction:

I want to check if I can predict the location of crimes 2019-12 based on data between 2018-11 and provided by police.co.uk:

enter description of image here

>>>df
    Crime ID    Month   Reported by Falls within    Longitude   Latitude    Location    LSOA code   LSOA name   Outcome type
0   2812fed4057622ce26bd11d76114fb8a85160d07883903...   2018-10 Metropolitan Police Service Metropolitan Police Service NaN NaN No location NaN NaN Investigation complete; no suspect identified
1   c5ae9dc7e6f60beeab970c11954b6f7eb5b05003fc6f07...   2018-10 Metropolitan Police Service Metropolitan Police Service NaN NaN No location NaN NaN Investigation complete; no suspect identified
2   e04f833e7ffea31719699b9ed0c591b738ab38f9c63d0b...   2018-10 Metropolitan Police Service Metropolitan Police Service -0.117669   51.552415   On or near STURMER WAY  E01002762   Islington 011C  Investigation complete; no suspect identified
...

So in general terms, what methods can I use to predict the next location given the previous one?

software – Tools or methods to extract image from higher resolution video by combining multiple images

With a stationary zoomed video, if you watch as a human, more detail can be "seen" on multiple frames as we are able to suppress noise and / or combine slightly offset details into a coherent understanding from the scene.

Is there any software that can do the same to extract an image from video with higher resolution than the video itself? Maybe using a traditional algorithm and / or AI.

What we're not interested in here is the super-resolution single-image AI upscaling that uses only one image as the source.

android – How can I execute these methods in java?

I am trying to execute the following methods in java at the press of a button, the first is a fly call which is responsible for bringing data from an API and the second is responsible for displaying the data obtained in the TextView of the screen. The following problem occurs, first the method that shows that the data is executed, then the one that is responsible for providing it.

By studying the problem a bit, I could say that the fly is executed asynchronously, then it allows the other processes to be executed without waiting for the execution of the request.

As the data is displayed first and then the query is made, it doesn't show me the data.

        ibtnBuscar.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                final ConexionApi conexionApi = new ConexionApi();
                try {
                    conexionApi.consultarProducto(getApplicationContext(),V_URL_MON, tCodigoLeido.getText().toString());
                    Toast.makeText(getApplicationContext(), "En los datos", Toast.LENGTH_SHORT).show();
                    cargarDatos();
                } catch (JSONException e) {
                    e.printStackTrace();
                } 
                //Se muestran los valores en la vista
            }
        });