TemplateDoesNotExist – Django Error

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I"m using Django Rest Framework. and I keep getting an error

Exception Type: TemplateDoesNotExist
Exception Value: rest_framework/api.html

I dont know how I"m going wrong. This is the first time I"m trying out hands on REST Framework. This is code.

views.py

import socket, json
from modules.data.models import *
from modules.utils import *
from rest_framework import status
from rest_framework.decorators import api_view
from rest_framework.response import Response
from modules.actions.serializers import ActionSerializer


@api_view(["POST"])
@check_field_exists_wrapper("installation")
def api_actions(request, format = None):

    action_type = request.POST["action_type"]
    if action_type == "Shutdown" : 
        send_message = "1"
        print "Shutting Down the system..."
    elif action_type == "Enable" : 
        send_message = "1"
        print "Enabling the system..."
    elif action_type == "Disable" : 
        send_message = "1"
        print "Disabling the system..."
    elif action_type == "Restart" : 
        send_message = "1"
        print "Restarting the system..."

    if action_type in ["Shutdown", "Enable", "Disable"] : PORT = 6000
    else : PORT = 6100

    controllers_list = Controller.objects.filter(installation_id = kwargs["installation_id"])

    for controller_obj in controllers_list:
        ip = controller_obj.ip
        try:
            s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            s.connect((ip, PORT))
            s.send(send_message)
            s.close()
        except Exception as e:
            print("Exception when sending " + action_type +" command: "+str(e))

    return Response(status = status.HTTP_200_OK)

models.py

class Controller(models.Model):
    id = models.IntegerField(primary_key = True)
    name = models.CharField(max_length = 255, unique = True)
    ip = models.CharField(max_length = 255, unique = True)
    installation_id = models.ForeignKey("Installation")

serializers.py

from django.forms import widgets from rest_framework import serializers from modules.data.models import *

class ActionSerializer(serializers.ModelSerializer):
    class Meta:
        model = Controller
        fields = ("id", "name", "ip", "installation_id")

urls.py

from django.conf.urls import patterns, url
from rest_framework.urlpatterns import format_suffix_patterns

urlpatterns = patterns("modules.actions.views",
    url(r"^$","api_actions",name="api_actions"),
)

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TemplateDoesNotExist - Django Error __del__: Questions

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.

2973

Answer #1

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

Here is another example where something is run approximately once a minute:

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

2973

Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

from time import sleep
sleep(0.1) # Time in seconds

TemplateDoesNotExist - Django Error __del__: Questions

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?

2639

Answer #1


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

List comprehension vs. lambda + filter

5 answers

I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items.

My code looked like this:

my_list = [x for x in my_list if x.attribute == value]

But then I thought, wouldn"t it be better to write it like this?

my_list = filter(lambda x: x.attribute == value, my_list)

It"s more readable, and if needed for performance the lambda could be taken out to gain something.

Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way‚Ñ¢ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)?

957

Answer #1

It is strange how much beauty varies for different people. I find the list comprehension much clearer than filter+lambda, but use whichever you find easier.

There are two things that may slow down your use of filter.

The first is the function call overhead: as soon as you use a Python function (whether created by def or lambda) it is likely that filter will be slower than the list comprehension. It almost certainly is not enough to matter, and you shouldn"t think much about performance until you"ve timed your code and found it to be a bottleneck, but the difference will be there.

The other overhead that might apply is that the lambda is being forced to access a scoped variable (value). That is slower than accessing a local variable and in Python 2.x the list comprehension only accesses local variables. If you are using Python 3.x the list comprehension runs in a separate function so it will also be accessing value through a closure and this difference won"t apply.

The other option to consider is to use a generator instead of a list comprehension:

def filterbyvalue(seq, value):
   for el in seq:
       if el.attribute==value: yield el

Then in your main code (which is where readability really matters) you"ve replaced both list comprehension and filter with a hopefully meaningful function name.

957

Answer #2

This is a somewhat religious issue in Python. Even though Guido considered removing map, filter and reduce from Python 3, there was enough of a backlash that in the end only reduce was moved from built-ins to functools.reduce.

Personally I find list comprehensions easier to read. It is more explicit what is happening from the expression [i for i in list if i.attribute == value] as all the behaviour is on the surface not inside the filter function.

I would not worry too much about the performance difference between the two approaches as it is marginal. I would really only optimise this if it proved to be the bottleneck in your application which is unlikely.

Also since the BDFL wanted filter gone from the language then surely that automatically makes list comprehensions more Pythonic ;-)

How do I do a not equal in Django queryset filtering?

5 answers

MikeN By MikeN

In Django model QuerySets, I see that there is a __gt and __lt for comparative values, but is there a __ne or != (not equals)? I want to filter out using a not equals. For example, for

Model:
    bool a;
    int x;

I want to do

results = Model.objects.exclude(a=True, x!=5)

The != is not correct syntax. I also tried __ne.

I ended up using:

results = Model.objects.exclude(a=True, x__lt=5).exclude(a=True, x__gt=5)
784

Answer #1

You can use Q objects for this. They can be negated with the ~ operator and combined much like normal Python expressions:

from myapp.models import Entry
from django.db.models import Q

Entry.objects.filter(~Q(id=3))

will return all entries except the one(s) with 3 as their ID:

[<Entry: Entry object>, <Entry: Entry object>, <Entry: Entry object>, ...]

We hope this article has helped you to resolve the problem. Apart from TemplateDoesNotExist – Django Error, check other __del__-related topics.

Want to excel in Python? See our review of the best Python online courses 2022. If you are interested in Data Science, check also how to learn programming in R.

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Schneider Richtgofen

San Francisco | 2022-12-07

Simply put and clear. Thank you for sharing. TemplateDoesNotExist – Django Error and other issues with filter was always my weak point 😁. Will get back tomorrow with feedback

Julia Schteiner

Vigrinia | 2022-12-07

I was preparing for my coding interview, thanks for clarifying this - TemplateDoesNotExist – Django Error in Python is not the simplest one. Will use it in my bachelor thesis

Jan Nickolson

New York | 2022-12-07

I was preparing for my coding interview, thanks for clarifying this - TemplateDoesNotExist – Django Error in Python is not the simplest one. I just hope that will not emerge anymore

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