Error while pushing to Heroku: requested runtime is not available for this stack


After creating a repository in Heroku, I want to push my project from master branch to my heroku repo.

On my first try I got the following error message:

No default language could be detected for this app

After searching, I used the following command:

heroku buildpacks:set heroku/python

Now it gave me this error message:

App not compatible with buildpack:

So now I tried everything from the beginning and it gives me the following error:

Python app detected

Requested runtime (“python-3.7.1”) is not
available for this stack (heroku-18).

I am stuck here.

I do have a requirements.txt with all the requirements and a runtime.txt in the same folder as my file.

Asked By: haneulkim



Python 3.7.1 is not supported by Heroku, as per their documentation on supported runtimes. Change the Python version to 3.7.2 if you want Python 3.7, or 3.6.8 if you don’t.

For information on specifying a runtime, see this page of the documentation. By default it uses 3.6.8 for Python, so if you want 3.7.2 you need to create a file called runtime.txt in the root directory of your app with python-3.7.2 written inside.

Answered By: Mihai Chelaru

Check your current version of Python:

C:Python --version


Python 3.8.5

Now goto runtime.txt & specify your version of Python:

Syntax: python-<version>


python-3.8.5 is CORRECT.

Python-3.8.5 is INCORRECT.

Python 3.8.5 is INCORRECT.

Answered By: Zahid Khan

In my case, my Runtime.txt was:

# Runtime.txt

I removed #Runtime.txt line, and it worked!
the app will assume you don’t have a python version installed and install the correct one for you. Its an automatic process

Additionally, you should commit the changes before pushing.

Answered By: KYHSGeekCode

Just upgrade the version in your runtime.txt file while pushing the code.
List of official supported python version in stacks –

  • python-3.9.4
  • python-3.8.9
  • python-3.7.10
  • python-3.6.13

For more details check –

Answered By: Ayaz Saiyed

In my case, my Runtime.txt was:

# Runtime.txt

Changed that to


Always check the dev centre to know the supported python versions.

Answered By: Dr.House
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