We Keep Coding

django NoReverseMatch not a valid view function or pattern name [duplicate]

I have some code and when it executes, it throws a NoReverseMatch, saying:
NoReverseMatch at /my_url/ Reverse for 'my_url_name' with arguments '()' and keyword arguments '{}' not found. n pattern(s) tried: []
What does this mean, and what can I do about it?

The NoReverseMatch error is saying that Django cannot find a matching url pattern for the url you've provided in any of your installed app's urls.
The NoReverseMatch exception is raised by django.core.urlresolvers when a matching URL in your URLconf cannot be identified based on the parameters supplied.
To start debugging it, you need to start by disecting the error message given to you.
NoReverseMatch at /my_url/
This is the url that is currently being rendered, it is this url that your application is currently trying to access but it contains a url that cannot be matched
Reverse for 'my_url_name'
This is the name of the url that it cannot find
with arguments '()' and
These are the non-keyword arguments its providing to the url
keyword arguments '{}' not found.
These are the keyword arguments its providing to the url
n pattern(s) tried: []
These are the patterns that it was able to find in your urls.py files that it tried to match against
Start by locating the code in your source relevant to the url that is currently being rendered - the url, the view, and any templates involved. In most cases, this will be the part of the code you're currently developing.
Once you've done this, read through the code in the order that django would be following until you reach the line of code that is trying to construct a url for your my_url_name. Again, this is probably in a place you've recently changed.
Now that you've discovered where the error is occuring, use the other parts of the error message to work out the issue.
The url name
Are there any typos?
Have you provided the url you're trying to access the given name?
If you have set app_name in the app's urls.py (e.g. app_name = 'my_app') or if you included the app with a namespace (e.g. include('myapp.urls', namespace='myapp'), then you need to include the namespace when reversing, e.g. {% url 'myapp:my_url_name' %} or reverse('myapp:my_url_name').
Arguments and Keyword Arguments
The arguments and keyword arguments are used to match against any capture groups that are present within the given url which can be identified by the surrounding () brackets in the url pattern.
Assuming the url you're matching requires additional arguments, take a look in the error message and first take a look if the value for the given arguments look to be correct.
If they aren't correct:
The value is missing or an empty string
This generally means that the value you're passing in doesn't contain the value you expect it to be. Take a look where you assign the value for it, set breakpoints, and you'll need to figure out why this value doesn't get passed through correctly.
The keyword argument has a typo
Correct this either in the url pattern, or in the url you're constructing.
If they are correct:
Debug the regex
You can use a website such as regexr to quickly test whether your pattern matches the url you think you're creating, Copy the url pattern into the regex field at the top, and then use the text area to include any urls that you think it should match against.
Common Mistakes:
Matching against the . wild card character or any other regex characters
Remember to escape the specific characters with a \ prefix
Only matching against lower/upper case characters
Try using either a-Z or \w instead of a-z or A-Z
Check that pattern you're matching is included within the patterns tried
If it isn't here then its possible that you have forgotten to include your app within the INSTALLED_APPS setting (or the ordering of the apps within INSTALLED_APPS may need looking at)
Django Version
In Django 1.10, the ability to reverse a url by its python path was removed. The named path should be used instead.
If you're still unable to track down the problem, then feel free to ask a new question that includes what you've tried, what you've researched (You can link to this question), and then include the relevant code to the issue - the url that you're matching, any relevant url patterns, the part of the error message that shows what django tried to match, and possibly the INSTALLED_APPS setting if applicable.

A very common error is when you get with arguments ('',). This is caused by something like this:
{% url 'view-name' does_not_exist %}
As does_not_exist doesn't exist, django evaluates it to the empty string, causing this error message.
If you install django-fastdev you will instead get a nice crash saying does_not_exist doesn't exist which is the real problem.

With django-extensions you can make sure your route in the list of routes:
./manage.py show_urls | grep path_or_name
If the route is missing you probably have not imported the application.

It may be that it's not loading the template you expect. I added a new class that inherited from UpdateView - I thought it would automatically pick the template from what I named my class, but it actually loaded it based on the model property on the class, which resulted in another (wrong) template being loaded. Once I explicitly set template_name for the new class, it worked fine.

The arguments part is typically an object from your models. Remember to add it to your context in the view. Otherwise a reference to the object in the template will be empty and therefore not match a url with an object_id.

Watch out for different arguments passing between reverse() and redirect() for example:
url(r"^some_app/(?P<some_id>\d+)/$", some_view_function, name="some_view")
will work with:
reverse("some_view", kwargs={"some_id": my_id})
and:
redirect("some_view", some_id=my_id)
but not with:
reverse("some_view", some_id=my_id)
and:
redirect("some_view", kwargs={"some_id": my_id})

URL pattern for query string parameters Django REST Framework

This is my current url path is as http://localhost:8000/api/projects/abcml/2021
and in the urls.py page I am passing as path("api/projects/<str:project_handle>/<int:year>", functionname...) and in the view, I accept this parameters with self.kwargs.get method.
I want to pass url as this format http://localhost:8000/api/projects/abcml/?year=2021
What changes do I need to make in url pattern?
I tried this path("api/projects/<str:project_handle>/?year=<int:year> but did not seem correct also in the view page, instead of self.kwargs.get I changed it to self.request.query_params.get for year parameter. That did not work either. Error it throwing is Page not found (404).

The query string [wiki] is not part of the path, and therefore can not be matched.
You thus specify as path:
path('api/projects/<str:project_handle>/', functionname)
In the view, you can access the data with self.request.GET['year'] and this will return a string or a KeyError in cas the year was not provided in the query string.

Why do I need to specify HTML file in render()

Why do I need to give html file name in render() - I have already set url in my project file in urls.py in django
urls.py
url('view-books',views.viewBooks)
views.py
def viewBooks(request):
books=models.Book.objects.all()
res=render(request,'BRMapp/view_book.html',{'books':books})
Why can I not give in render view-books?

i think you have typo
def viewBooks(request):
books=models.Book.objects.all()
context = {"books":book}
return render(request,'BRMapp/view_book.html',context)
your question why you need html file name in render because render is a function it takes 3 arguments 1st is request second is "path of the html file" 3rd is the context
further explaination
Do you have basic idea how django work first of first you are not giving url in render you are giving path to render which template should be render . django follow mvc pattern you read on it but to simplify it urls just have the routing task they are just there to filter routes not to do any thing in url you can give 3 arguments two are compulsary first the path by which it recognize that the time has come to act the second the function name which direct him where to go then its function responsibilty to process the data

Unfortunately, you didn't return anything in your view. So you need to add return to your function:
def viewBooks(request):
books=models.Book.objects.all()
return render(request,'BRMapp/view_book.html', {'books':books})
You might want to take a look at this tutorial.

https://yourwebsite/view-book is not the same as BRMapp/view_book.html, Django needs to know that one corresponds to the other.
The routing in Django works like this:
The user sends a request to Django with a url.
Django looks through your urls in urls.py for a path that matches what was requested.
When it finds a path, like view-books, that path has a view. The view is just a function (viewBooks()), and Django executes it.
The view function is expected to return the content that the user will see. You could, if you wanted, write the whole page by hand as a string in the return line of viewBooks(), but that's inconvenient, so instead you tell Django to make the page for you, starting from a template. To do so, you call render().
What render() does is take the template and replace all parts that need to be replaced for the user that will see it. But to know what the initial content will look like, it needs to read it from somewhere, and that's the HTML file BRMapp/view_book.html.
The HTML file doesn't need to have the same name as the view, you could have called it foobar.html and it would have worked the same. But regardless of its name, you need to tell Django that you want to use a file (render() tells Django that), and you need to tell Django where that file is. You'll have many different files in different places with different names, and it can happen that you have the same name for templates in different directories, so Django will not attempt to guess which one you want: you'll have to put its path inside render() so that Django knows where to start building the page.
If you gave the URL to render() instead of the path to the file, Django would get to point 5 and then back again to 1 to figure out what that URL means, and so on and so forth forever.

How to fix NoReverseMatch error in Django [duplicate]

I have some code and when it executes, it throws a NoReverseMatch, saying:
NoReverseMatch at /my_url/ Reverse for 'my_url_name' with arguments '()' and keyword arguments '{}' not found. n pattern(s) tried: []
What does this mean, and what can I do about it?

The NoReverseMatch error is saying that Django cannot find a matching url pattern for the url you've provided in any of your installed app's urls.
The NoReverseMatch exception is raised by django.core.urlresolvers when a matching URL in your URLconf cannot be identified based on the parameters supplied.
To start debugging it, you need to start by disecting the error message given to you.
NoReverseMatch at /my_url/
This is the url that is currently being rendered, it is this url that your application is currently trying to access but it contains a url that cannot be matched
Reverse for 'my_url_name'
This is the name of the url that it cannot find
with arguments '()' and
These are the non-keyword arguments its providing to the url
keyword arguments '{}' not found.
These are the keyword arguments its providing to the url
n pattern(s) tried: []
These are the patterns that it was able to find in your urls.py files that it tried to match against
Start by locating the code in your source relevant to the url that is currently being rendered - the url, the view, and any templates involved. In most cases, this will be the part of the code you're currently developing.
Once you've done this, read through the code in the order that django would be following until you reach the line of code that is trying to construct a url for your my_url_name. Again, this is probably in a place you've recently changed.
Now that you've discovered where the error is occuring, use the other parts of the error message to work out the issue.
The url name
Are there any typos?
Have you provided the url you're trying to access the given name?
If you have set app_name in the app's urls.py (e.g. app_name = 'my_app') or if you included the app with a namespace (e.g. include('myapp.urls', namespace='myapp'), then you need to include the namespace when reversing, e.g. {% url 'myapp:my_url_name' %} or reverse('myapp:my_url_name').
Arguments and Keyword Arguments
The arguments and keyword arguments are used to match against any capture groups that are present within the given url which can be identified by the surrounding () brackets in the url pattern.
Assuming the url you're matching requires additional arguments, take a look in the error message and first take a look if the value for the given arguments look to be correct.
If they aren't correct:
The value is missing or an empty string
This generally means that the value you're passing in doesn't contain the value you expect it to be. Take a look where you assign the value for it, set breakpoints, and you'll need to figure out why this value doesn't get passed through correctly.
The keyword argument has a typo
Correct this either in the url pattern, or in the url you're constructing.
If they are correct:
Debug the regex
You can use a website such as regexr to quickly test whether your pattern matches the url you think you're creating, Copy the url pattern into the regex field at the top, and then use the text area to include any urls that you think it should match against.
Common Mistakes:
Matching against the . wild card character or any other regex characters
Remember to escape the specific characters with a \ prefix
Only matching against lower/upper case characters
Try using either a-Z or \w instead of a-z or A-Z
Check that pattern you're matching is included within the patterns tried
If it isn't here then its possible that you have forgotten to include your app within the INSTALLED_APPS setting (or the ordering of the apps within INSTALLED_APPS may need looking at)
Django Version
In Django 1.10, the ability to reverse a url by its python path was removed. The named path should be used instead.
If you're still unable to track down the problem, then feel free to ask a new question that includes what you've tried, what you've researched (You can link to this question), and then include the relevant code to the issue - the url that you're matching, any relevant url patterns, the part of the error message that shows what django tried to match, and possibly the INSTALLED_APPS setting if applicable.

A very common error is when you get with arguments ('',). This is caused by something like this:
{% url 'view-name' does_not_exist %}
As does_not_exist doesn't exist, django evaluates it to the empty string, causing this error message.
If you install django-fastdev you will instead get a nice crash saying does_not_exist doesn't exist which is the real problem.

With django-extensions you can make sure your route in the list of routes:
./manage.py show_urls | grep path_or_name
If the route is missing you probably have not imported the application.

It may be that it's not loading the template you expect. I added a new class that inherited from UpdateView - I thought it would automatically pick the template from what I named my class, but it actually loaded it based on the model property on the class, which resulted in another (wrong) template being loaded. Once I explicitly set template_name for the new class, it worked fine.

The arguments part is typically an object from your models. Remember to add it to your context in the view. Otherwise a reference to the object in the template will be empty and therefore not match a url with an object_id.

Watch out for different arguments passing between reverse() and redirect() for example:
url(r"^some_app/(?P<some_id>\d+)/$", some_view_function, name="some_view")
will work with:
reverse("some_view", kwargs={"some_id": my_id})
and:
redirect("some_view", some_id=my_id)
but not with:
reverse("some_view", some_id=my_id)
and:
redirect("some_view", kwargs={"some_id": my_id})

Remove whitespaces from a url in Urlpatterns (django)

I'm new to Django and I'm developing a project in which there are profile pages.
Well, the problem is that the primary key has whitespaces but I don't want them to show in the url, neither like "%20%", I want to join the words. For example:
website.com/Example Studios --> website.com/examplestudios
I've tried this:
url ( (r'^(?P<studio_name>[\w ]+)/$').replace(" ", ""), views.StudioView, name = 'dev_profile')
But didn't work (it seems like it turns the raw part to string before reading the url) and with 're' happens the same. I've been searching for solutions but I'm not able to find them (and slugify doesn't convinces me).
What's solution to this or what do you recommend?

In urls you define patterens which Django will catch e.g. r'^test/$' this means that when someone try to get yourdomain.com/test Django will catch it and call the view which will probably render template. You need to solve your problem on url generation e.g. in template . Therefore in urls:
url ( (r'^(?P<studio_name>[\w ]+)/$'), views.StudioView, name = 'dev_profile').
You need to transform primary key to word without space in template. One way is to use slug for every record.
Also add slug field to Studio model which is autogenerated and non-editable field(you can generate it from name e.g. Example Studios->examplestudios).