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I can't deploy my Flask app to Heroku... I've searched in every thread I can and nothing worked for me : add a runtime.txt, set a buildpack. I don't know what can be wrong now.

Here is my root directory for the app : 

Project
 - .git
 - Procfile
 - Readme.md
 - app
 - config.py
 - requirements.txt
 - runtime.txt
 - web.py

Here's the content of requirements.txt:

appdirs==1.4.3
click==6.7
Flask==0.12.1
Flask-WTF==0.14.2
itsdangerous==0.24
Jinja2==2.9.5
MarkupSafe==1.0
packaging==16.8
pyparsing==2.2.0
six==1.10.0
Werkzeug==0.12.1
WTForms==2.1

The Procfile : 

web: python web.py

And the runtime.txt:

python-2.7.13

When I do git push heroku master, it prints:

remote: Compressing source files... done.
remote: Building source:
remote:
remote:  !     No default language could be detected for this app.
remote:             HINT: This occurs when Heroku cannot detect the buildpack to use for this application automatically.
remote:             See https://devcenter.heroku.com/articles/buildpacks
remote:
remote:  !     Push failed
remote: Verifying deploy...
remote:
remote: !   Push rejected to appname.
remote:

I tried to add a buildpack with heroku buildpacks:add heroku/Python but then it says that it can't detect app for python buildpack.

What could I possibly did wrong ?

Steph D.
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  • See also [Heroku Python failed to detect app matching buildpack - Stack Overflow](https://stackoverflow.com/questions/43228526/heroku-python-failed-to-detect-app-matching-buildpack) // [python - Heroku buildpack error while pushing - Stack Overflow](https://stackoverflow.com/questions/49840472/heroku-buildpack-error-while-pushing/49840654#49840654) // [django - Heroku: No default language could be detected for this app for python even with runtime.txt - Stack Overflow](https://stackoverflow.com/questions/44232967/heroku-no-default-language-could-be-detected-for-this-app-for-python-even-with) – user202729 Aug 19 '21 at 01:42

5 Answers5

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Change requirements.py to requirements.txt.

If you're using the default Python 2.7.13 you shouldn't need a runtime.txt. You'd think that specifying the runtime would trigger the language detection but even without packages to install, Heroku requires an empty requirements.txt.

brennan
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I was spend time with a very similar error.

In my case, i tried to deploy a django app.

I just run these commands to setup the buildpack

  heroku login
  heroku create --stack cedar --buildpack git://github.com/heroku/heroku-buildpack-python.git
  heroku config:add BUILDPACK_URL=git@github.com:heroku/heroku-buildpack-python.git#purge
  heroku config:set HEROKU=1

I decided to post this here because it took me a long time to get these tips

Guilherme
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edit the content of your Procfile to

web: gunicorn web:app --log-file=-

I assume your web.py file is contained in your project's root folder i.e you see it once you enter your project's "Project" folder.

Otherwise, if it is contained in the app folder then use 

web: gunicorn app.web:app --log-file=-
Nuelsian
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I also run into similar problem. I was able to fix it by adding the runtime.txt

just put the version of the python you are using in the runtime.txt

python-2.7.14
Oyetoke Tobi
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I'm late the to party but if you already have a requirements.txt file and you're getting this error, try adding a Procfile like shown here in the documentation: https://devcenter.heroku.com/articles/getting-started-with-python#define-a-procfile

caceves
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