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 patte(s) tried: []
What does this mean, and what can I do about it?
The NoReverseMatch error is saying that Django caot find a matching url patte 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 caot 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 caot be matched
Reverse for 'my_url_name'
This is the name of the url that it caot 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 patte(s) tried: []
These are the pattes 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 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 patte.
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 patte, 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 patte matches the url you think you're creating, Copy the url patte 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 patte you're matching is included within the pattes tried
If it isn't here then its possible that you have forgotten to include your app within the INSTALLED_APPS setting
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 pattes, the part of the error message that shows what django tried to match, and possibly the INSTALLED_APPS setting if applicable.
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