Julio Cesar's questions

I have a problem with the following code:

import subprocess

process = subprocess.run(
    ['mkdir', 'hola'], stdout = subprocess.PIPE, stderr = subprocess.PIPE, shell = True
)

print(process.stderr)
print(process.stdout)

It does not create the "hello" folder, but the strange thing is that the process gives the following error:

b"mkdir: falta un operando\nPruebe 'mkdir --help' para m\xc3\xa1s informaci\xc3\xb3n.\n" # print(process.stderr)

It's like passing it as the first parameter ['mkdir']instead of ['mkdir', 'hola'], but I don't know.

Also try the following: ['cp', 'file1.txt', 'file2.txt']and something similar happened:

b"cp: falta un fichero como operando\nPruebe 'cp --help' para m\xc3\xa1s informaci\xc3\xb3n.\n"

What's going on? (a few days ago, it worked fine... and I have no idea why it doesn't work now)

I had a question about what exactly is the class or object objectin Python.

As far as I know, in Python everything is created by the metaclass type(but from what I will explain next it makes me doubt):

>>> str.__class__
<class 'type'>
>>> int.__class__
<class 'type'>
>>> bool.__class__
<class 'type'>
>>> float.__class__
<class 'type'>
>>> class A:
...     pass
... 
>>> A.__class__
<class 'type'>
>>> ClassName = type('ClassName', (), {})
>>> ClassName.__class__
<class 'type'>

On the other hand objectit is an instance of type:

>>> object.__class__
<class 'type'>
>>> isinstance(object, type)
True

What doesn't work for me at all is this:

>>> isinstance(type, object)
True

How can it possibly typebe an instance of objectif it's supposed to objectbe an instance of type? Has no sense. Looks like Python is contradicting itself...

In addition to this, it objectis a base class of type:

>>> type.__bases__
(<class 'object'>,)

But according to Python objectit is an instance of typeand according to that, how is it possible for a class ( type) to inherit from an instance ( object) of said class?

So based on this: What exactly is typeand object? Which of the two is the "true" metaclass or "the class that creates classes" so to speak? As I understood it was type:

type('MyClass', (), {})

And out of curiosity to know more about object, it seems that all classes inherit or descend from it:

>>> int.__bases__
(<class 'object'>,)
>>> bool.__bases__
(<class 'int'>,)
>>> str.__bases__
(<class 'object'>,)
>>> float.__bases__
(<class 'object'>,)
>>> class A:
...     pass
... 
>>> A.__bases__
(<class 'object'>,)

Why is it like this?

This is my class:

class User():

    ...

    def __getattribute__(self, name):
        if name not in ['create_user', 'authenticate_user']:
            x = super().__getattribute__('authenticate_user')
            print(x)

        return super().__getattribute__(name)

I want to get the value of the method authenticate_user, but I can't.

In this part:

x = super().__getattribute__('authenticate_user')

I only get the method, but I want to execute it in order to obtain the value that the method returns. But when you run it:

x = super().__getattribute__('authenticate_user')()

I get an error of RecursionError: maximum recursion depth exceeded.

And I have no idea how to call the method without giving me that error or some solution.

Is there a way to call such a method in the method __getattribute__? Any solution?

I was doing some tests with python trying to "force", so to speak, the encapsulation in python, since in python private attributes do not exist as such:

import re

class Mixin(object):
    __a = 1

    def __getattribute__(self, name):
        if re.match(f'_{ self.__class__.__name__ }__', name):
            raise AttributeError(f"'{ self.__class__.__name__ }' object has no attribute '{ name }'")

        return super().__getattribute__(name)

Mixin()._Mixin__a

It is assumed that in this way the attribute could not be accessed __alike this: _Mixin__a.

But it gives me the following error:

Traceback (most recent call last):
  File "/home/lcteen/Documentos/Programming/Python/Practices/sss.py", line 24, in <module>
    Mixin()._Mixin__a
  File "/home/lcteen/Documentos/Programming/Python/Practices/sss.py", line 19, in __getattribute__
    if re.match(f'_{ self.__class__.__name__ }__', name):
  File "/home/lcteen/Documentos/Programming/Python/Practices/sss.py", line 19, in __getattribute__
    if re.match(f'_{ self.__class__.__name__ }__', name):
  File "/home/lcteen/Documentos/Programming/Python/Practices/sss.py", line 19, in __getattribute__
    if re.match(f'_{ self.__class__.__name__ }__', name):
  [Previous line repeated 996 more times]
RecursionError: maximum recursion depth exceeded

I do not understand what I am doing wrong, nor why the error occurs.

I've come across different syntax in various pieces of code, mostly only seen when using Django, not Python itself.

For example, when adding a verbose_nameto a field in Django, they do it as follows:

title = models.CharField(_('Titulo'), max_length = 200)

With that strange syntax of _(''), they also use it when putting a verbose_nameand a verbose_name_pluralto a model, as follows:

class Meta:
    verbose_name = _('app')
    verbose_name_plural = _('apps')

They could have done it as follows:

class Meta:
    verbose_name = 'app'
    verbose_name_plural = 'apps'

But they didn't do it, so why with that syntax? Is it advantageous to do it that way? Why do they only use it when working with Django and not in Python as such?

It is a doubt that I have always had, but I have never found information about it. Thanks in advance for your answers!

I have the doubt of which is the correct way to save videos or upload them, in Django.

The fieldone that could work, I think, would be a FileField, but is this a good option or alternative?

I also saw a proposal out there to have a field FilePathField, having the video paths there and thus accessing them when necessary, but I'm not very convinced.

Any suggestion helps my learning. Thanks in advance for your answers!

I have a problem with socketsin python. Here my code:

File server.py:

import subprocess
import socket

def run_command(command):
    process = subprocess.run(command.split(), stdout = subprocess.PIPE, stdin = subprocess.PIPE,)
    return process.stdout

skt = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
skt.bind(('localhost', 9999))

skt.listen(5)

while True:
    client_socket, addr = skt.accept()

    while True:
        received = client_socket.recv(1024)
        client_socket.send(run_command(received))

File client.py:

import socket

client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect(('localhost', 9999))

while True:
        client_socket.send(
            input('>> ').encode('utf-8')
        )

        received = client_socket.recv(2024)
        print(received)

client_socket.close()

The purpose is to be able to execute commands, but when doing so the first problem arises, the problem consists in how it prints the output of the terminal, example:

>> ls
b'client.py\nproyect.py\nserver.py\ntest.py\n'
>> apt
b'apt 1.6.11 (amd64)\nUso: apt [opciones] orden\n\napt es un gestor de paquetes de l\xc3\xadnea de \xc3\xb3rdenes y proporciona \xc3\xb3rdenes\npara la b....

How is it done to be able to print the output of the terminal in a "normal" way, so to speak, and not make it look ugly?

I also run into the problem that when executing many commands an error occurs. Here an example:

>> ls
b'client.py\nproyect.py\nserver.py\ntest.py\n'
>> ls
b'client.py\nproyect.py\nserver.py\ntest.py\n'
>> ls
b'client.py\nproyect.py\nserver.py\ntest.py\n'
>> ls
b'client.py\nproyect.py\nserver.py\ntest.py\n'
>> cd  ..
b''
>> ls
b''
>> ls
Traceback (most recent call last):
  File "client.py", line 8, in <module>
    input('>> ').encode('utf-8')
BrokenPipeError: [Errno 32] Broken pipe

Is there a way to fix this? I'm pretty new to this theme sockets. Thanks in advance for your answers!.

Update:

I managed to solve the problem of aesthetics, making the output of the terminal look "pretty", by adding .decode('utf-8')data received from the socketserver.

I have a problem with my urlsen Django, here my urls.py:

from .views import (
    CouponListView, CouponDetailView, buy_coupon, UserCouponListView, CouponOfResaleCreateView,
    CouponOfResaleListView,
) 

from django.urls import path, include

coupons_patterns = ([
    path('', CouponListView.as_view(), name = 'list'),
    path('<slug:slug>/', UserCouponListView.as_view(), name = 'user'),
    path('<int:pk>/<slug:slug>/', CouponDetailView.as_view(), name = 'detail'),
    path('coupon/<int:pk>/buy-<slug:slug>/', buy_coupon, name = 'buy-coupon'),

    path('resale/', include([
        path('', CouponOfResaleListView.as_view(), name = 'resale_list'),
        path('create/<int:pk>/<slug:slug>/', CouponOfResaleCreateView.as_view(), name = 'create'),
    ])),

], 'coupons')

The ones urlsthat don't work or don't respond are these:

path('resale/', include([
        path('', CouponOfResaleListView.as_view(), name = 'resale_list'),
        path('create/<int:pk>/<slug:slug>/', CouponOfResaleCreateView.as_view(), name = 'create'),
])),

I don't get an error, they just don't respond, that is, if I want to access one of the urlsones that I showed previously, for example, resale_listinstead of showing me what it should show me, it shows me the result of accessing the url user.

In the urlbrowser is the urlcorrectly but it shows me the HTML of another url, which in this case is the url user.

The way to fix it is to move that portion on urlstop, as follows:

coupons_patterns = ([
    path('resale/', include([
        path('', CouponOfResaleListView.as_view(), name = 'resale_list'),
        path('create/<int:pk>/<slug:slug>/', CouponOfResaleCreateView.as_view(), name = 'create'),
    ])),

    path('', CouponListView.as_view(), name = 'list'),
    path('<int:pk>/<slug:slug>/', CouponDetailView.as_view(), name = 'detail'),
    path('coupon/<int:pk>/buy-<slug:slug>/', buy_coupon, name = 'buy-coupon'),
    path('<slug:slug>/', UserCouponListView.as_view(), name = 'user'),

], 'coupons')

Another solution is to move the url userbelow said portion of urls, as follows:

coupons_patterns = ([
    path('', CouponListView.as_view(), name = 'list'),
    path('<int:pk>/<slug:slug>/', CouponDetailView.as_view(), name = 'detail'),
    path('coupon/<int:pk>/buy-<slug:slug>/', buy_coupon, name = 'buy-coupon'),

    path('resale/', include([
        path('', CouponOfResaleListView.as_view(), name = 'resale_list'),
        path('create/<int:pk>/<slug:slug>/', CouponOfResaleCreateView.as_view(), name = 'create'),
    ])),

    path('<slug:slug>/', UserCouponListView.as_view(), name = 'user'),

], 'coupons')

But why does this happen? Because depending on the order of the urlscauses this problem to happen?

Any solution? Since I don't like to have my files urlsin that order for them to work.

I have an interesting problem, first of all the model itself:

class Reserva(models.Model):
    cliente = models.CharField(max_length = 200)
    empleado_de_turno = models.ForeignKey(User, on_delete = models.CASCADE)

The problem consists:

Create an instance of the model Reservathrough the view CreateView, which will create a form to create said instance, but in the form I do not want the field to be displayed, empleado_de_turnoI want only the field to be displayed clienteand that by default the value of the field empleado_de_turnois the user that login at that time.

Well to fix the said problem, try modifying the data sent by the POST method, in the method get_form_kwargs:

class ReservaCreateView(CreateView):
    model = Reserva
    template_name = 'testapp1/example.html'
    fields = ['cliente']
    success_url = reverse_lazy('home')

    def get_form_kwargs(self):
        form_kwargs = super().get_form_kwargs()
        if form_kwargs.get('data'):
            user = User.objects.get(username = self.request.user)
            post = self.request.POST.copy()
            post['empleado_de_turno'] = str(user.pk)
            form_kwargs['data'] = post

        return form_kwargs

The thing is that it doesn't work for me, I always get this error:

django.db.utils.IntegrityError: NOT NULL constraint failed: testapp1_reserva.empleado_de_turno_id

I started trying to figure out where exactly the error occurred, because the method solution get_form_kwargsthat I showed before, should fix the error, and the error occurs in the method form_valid, specifically in the form.save(), here the source code of the method form_valid:

ModelFormMixin:

 def form_valid(self, form):
     """If the form is valid, save the associated model."""
     self.object = form.save()
     return super().form_valid(form)

FormMixin:

def form_valid(self, form):
    """If the form is valid, redirect to the supplied URL."""
    return HttpResponseRedirect(self.get_success_url())

IMPORTANT

I did the following with the intention of seeing how the data structure is when the instance was created, without omitting fields and when the field was omitted empleado_de_turno, in order to be able to replicate the structure when omitting said field and when modifying said data, and thus be able to solve the problem, avoiding errors

Case 1:

In the method form_valid, I printed form.datawhen the attribute fieldshad the following value:

fields = ['cliente']

Case 2:

Later I did the same but in this case the attribute fieldshad the following values:

fields = ['cliente', 'empleado_de_turno']

I printed the following in the data method form_valid, since this was where the error specifically arose and it was possible that the data was not being sent as I modified it previously:

def form_valid(self, form):
    print(form.data)

The result of printing it in the 2 cases was as follows:

<QueryDict: {'csrfmiddlewaretoken': ['SBRSJa0aw4iNJOMPwtQVsFL6V6y1cFMNGne9Kr0fA7YmtYeD8xshhDq6pc1mKjQs'], 'cliente': ['code2'], 'empleado_de_turno': ['1']}>

That means that whether you print form.datain Case 1 or in Case 2 , the data is exactly the same, which means that the problem is not the data at the time of modifying it, it is something else (I deduce).

Since even when printing form.is_validin the method form_valid, it returns True.

So , why does it give an error, if I am replicating the data structure correctly when modifying it? I do not find sense in this error, I am doing the whole modification process correctly.

Update:

Many think that in reality the field empleado_de_turnoexpects forman object in the or in the view, I sent an idand they may think that this is the error, but it is not.

First of all, I already tried it, instead of putting a idin the field empleado_de_turno, I put an object, and it gave the same error.

The reason that the field empleado_de_turnoexpects a idand not an object is because that is how the view manages it, at least when receiving the data through the POST method, I don't know why it manages it that way, that is how the developers decided of Django.

This can be verified in Case 2 , no field is omitted, the two fields are filled normally and form_validthe data entered is printed in the method as follows: form.data.

Printing it results in:

<QueryDict: {'csrfmiddlewaretoken': ['SBRSJa0aw4iNJOMPwtQVsFL6V6y1cFMNGne9Kr0fA7YmtYeD8xshhDq6pc1mKjQs'], 'cliente': ['code2'], 'empleado_de_turno': ['1']}>

It can clearly be seen that the key empleado_de_turnovalue is a id, not an object.

There you can check that the field empleado_de_turnodoes not expect an object as such, at least not at that stage of the view.

I have a problem with HTML, for example, I have a container, inside the container I have several elements and among them there is an element <p>, the problem is that there comes a point in which the text inside <p>is too much and causes the text or the <p>comes out of the container.

This is because I established a widthdel 20%, and it needs to have that width, my question is, how do I make it so that instead of continuing the text in length, when it is at the limit of the container, it does a line break?

This would be my HTML file:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="main.css">
    <title>Document</title>
</head>
<body>
    <div class="container">
        <div class="column">
            <h2>Tituloooooooooooo</h2>
            <p class="price">500$</p>
            <p>aaaaaaaaaaaaaaaaaddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd</p>
        </div>
        <div class="column">
            <h2>Tituloooooooooooo</h2>
            <p class="price">500$</p>
            <p class="">aaaaaaaaaaaaaaaaa</p>
        </div>
    </div>
</body>
</html>

And this my CSS file:

.container {
    display: flex;
    justify-content: flex-start;
    flex-flow: wrap;
    border: 1px solid black;
    padding: 10px;
}

.column {
    border: 1px solid black;
    padding: 10px;
    margin: 5px 12px 25px 12px;
    width: 20%;
}

This would be the image of how the result is displayed:

Thanks in advance for your answers!

I have a question regarding signals in Django.

According to the documentation Djangothere are two ways to connect a receiver to a signal in Django, the first would be with the method connect()- ( Signal.connect()) and the second way, which would alternatively be used, would be a decoratorreceiver()

My question is which is the best option to use? And what are the advantages and disadvantages of using the respective option, either with the method connect()or with the decorator receiver()?

In my opinion, the second way would be a better option, with the decorator receiver(), specifically because of the syntax that must be used to carry it out.

The only difference I find between using method 1 or 2 is the syntax, no more. That's why I have my doubt.

Thanks in advance for your answers!

I have a question about the library subprocess:

Why, when capturing the output of the terminal, either in Popen()or in subprocess.run(), do we have to give the argument stdoutthe value of subprocess.PIPEto capture the output correctly?

According to it subprocess.PIPEis a pipe, but what is a pipe according to the library subprocessor according to python? And why precisely do you have to use pipes to capture the output of the terminal?

I haven't found much information on exactly what pipes are.

Thanks in advance for your answers!

I have a question about the library subprocess:

What is the difference between using subprocess.run()and Popen()and in what circumstances should each be used?

I have a problem with the property flexin css: I am giving it a value of justify-content: flex-startto order my HTML elements, the problem is that the number of elements can increase or decrease, and when the elements increase, the elements get smaller and smaller until they become deformed my layout.

Is there a way that once there is a certain amount of elements, the other elements go down to the second line or second block?

I found a Loop forwith a somewhat different syntax, I tried to find out how it worked but I couldn't, it gave me an error.

I began to investigate but I did not find much information, according to its syntax it is an for"asynchronous" loop or something like that, this would be the loop forI am talking about:

async for target in iter:
    block

Well my question is what is this loop for for? How does it work? And under what circumstances should it be used?

I also realized that there is not only a loop forwith that different syntax( async), there are functions, withsand I don't know if there are more.

async def funcname(parameter_list):
    pass

async with expr as var:
    block

So why asyncbefore declaring a loop for, a function, etc?

Thanks in advance for your answers!

I have a question about django, my question is what exactly is this?:

<class 'messenger.models.Thread_messages'>

I get it from a signal, but it's not an object or instance since I already get an instance in the signal, I could get all model instances with it, as follows (and it works):

x = <class 'messenger.models.Thread_messages'>
x.objects.all()

But what is it exactly? Thanks in advance for your answers!

I have a question when sending an object to me DetailView:

class ProfileDetailView(DetailView):
    model = Profile
    template_name = 'profiles/profile_detail.html'

    def get_object(self):
        return get_object_or_404(Profile, user__username=self.kwargs['username'])

This would be my model Profile:

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete = models.CASCADE)
    avatar = models.ImageField(upload_to = custom_upload_to, null = True, blank = True)
    biography = models.TextField(null = True, blank = True)
    link = models.URLField(max_length = 200, null = True, blank = True)

My first question is, which field am I referring to in this part of the code?: ...,user_username=self...)Am I referring to usernamethe model Userfield or the usermodel field Profile?

My second question is why is there a reference to this field in this strange way?:user__username

And well, my last question is, how is it that get_objectthe dictionary receives the method self.kwargs? And how is it that the usernameuser's dictionary is found in that dictionary? I also saw that you could access the pkobject, through the self.kwargs, but I don't receive the pk, why is that?

Thanks in advance for your answers!

I have a doubt and which is better reverseor reverse_lazy?, I saw somewhere that it was better reverse_lazyand that it is better to use it reverse_lazyin everything, because it is a function that is executed at runtime and should not be validated during Django loading. and that reversethere is a possibility that it is not validated in execution, something like that....

I mean that for example instead of using in the method get_success_url, reverseit is better to use reverse_lazysince it is better. (As explained above.)

def get_success_url(self):
    return reverse_lazy('pages:pages')

Practically that reverse_lazyalmost completely replaces reverse(well not so exaggerated) Well I hope I make myself understood.

But I still can't understand very well what is the difference between reverseand reverse_lazyand which is better. Also, how exactly does each one work?

Thanks in advance for your answers!

I don't quite understand how this ' for ' loop works in this list:

lista_1 = ['a', 'b', 'c']
lista_2 = [i for i in lista_1]
print(lista_1)

If I understand the loop, what I don't understand is why before the ' for ' loop there is the ' i ' if I remove it it gives an error, so my question is why is the ' i ' placed in that place?

Thanks in advance for your answers!

I have a question, what is the correct way to define a variable in python3? I mean if it is correct to define it starting with a capital letter, like this:

Capital letter:

self.Var = 1
Variable = 1

OR Lowercase:

self.varInt = 1
variable = 1

And also, what is the correct way to define control variables, StringVar, IntVar, etc?

Is it correct to define it with self.?