Check if my application runs in development/editable mode

Question

My Python application can be install the normal way, or in development/editable mode with pip, like this:

virtualenv my_app
source my_app/bin/activate
pip install -e my_app

How can I make a function to introspect my virtualenv and check if my application runs in development/editable mode?

Is there any "flag" in sys module for that?

Motivation: have different configuration in development mode, and in production.

EDIT: I compare the virtualenv and the package directories.

import os
import sys

import pkg_resources

main_pkg = 'my_app'
package_dir = pkg_resources.resource_filename(main_pkg, '__init__.py')
virtualenv_dir = os.path.dirname(os.path.dirname(sys.executable))
common_path = os.path.commonprefix([package_dir, virtualenv_dir])
is_dev_mode = not common_path.startswith(virtualenv_dir)

I test if the package_dir is a subdirectory of the virtualenv_dir: if it is not a subdirectory, then I am on development mode.

EDIT2:

Is there a more reliable solution?

I want to know if there isn’t a data/a flag in the environment that would clearly indicate to me that my application is running in development mode.

What will happen if another dependency is in development mode too?

Answer 1

Using code from pip we can determine this:

import pip
import pkg_resources

# I've done `pip install -e .` for a git repo I'm working in inside
# a virtualenv
distributions = {v.key: v for v in pkg_resources.working_set}
# >>> distribution
# pre-commit 0.9.3 (/home/asottile/workspace/pre-commit)
distribution = distributions['pre-commit']

# Below is approximately how `pip freeze` works, see the end of
# the answer for a simpler approach, still using pip

# Turn into a pip FrozenRequirement (I'm using pip 9.0.1, it may
# be different for your version)
# I've passed an empty list for the second argument (dependency_links)
# I don't think it's necessary?
frozen_requirement = pip.FrozenRequirement.from_dist(distribution, [])

# Query whether the requirement is installed editably:
print(frozen_requirement.editable)

The magic of this comes from a little function inside pip (pip.utils):

def dist_is_editable(dist):
    """Is distribution an editable install?"""
    for path_item in sys.path:
        egg_link = os.path.join(path_item, dist.project_name + '.egg-link')
        if os.path.isfile(egg_link):
            return True
    return False

The dist in this is a pkg_resources distribution (as we acquired above). You of course can use the dist_is_editable function directly instead of going through FrozenRequirement:

# With `distribution` as above:
from pip.utils import dist_is_editable
print(dist_is_editable(distribution))  # True in my case ;)

Answer 2

The top solution needs updating for a more recent version of pip, where the FrozenRequirement class is no longer accessible in pip's namespace.

I used this workaround in the relevant lines.

from pip._internal.operations.freeze import FrozenRequirement 
frozen_requirement = FrozenRequirement.from_dist(distribution)