Detection of flake8 is inconsitent/broken in some cases

Environment data

• VS Code version: 1.23.1
• Extension version (available under the Extensions sidebar): 2018.5.0
• OS and version: Ubuntu 16.04 (w/ latest updates)
• Python version (& distribution if applicable, e.g. Anaconda): 3.6.5
• Type of virtual environment used (N/A | venv | virtualenv | conda | …): pipenv/virtualenv
• Relevant/affected Python packages and their versions:
  • pipenv, version 11.10.0

Actual behavior

“Linter Flake8 is not installed.” notification box pops up every time I try to save a Python file.

Expected behavior

Flake8 linting works for python file

Steps to reproduce:

1. pipenv --python 3.6 shell
2. code .
3. pipenv install flake8 --dev
4. Open Python file in VS code, edit, save.

But, in the VS Code “Terminal” tab, I can do:

(tarsnap-prune-0dGG-SaN)rsyring@loftey:~/projects/tarsnap-prune$ pip freeze
flake8==3.5.0
mccabe==0.6.1
pycodestyle==2.3.1
pyflakes==1.6.0
sh==1.12.14
(tarsnap-prune-0dGG-SaN)rsyring@loftey:~/projects/tarsnap-prune$ python
Python 3.6.5 (default, Mar 29 2018, 03:28:50)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import flake8
>>>
(tarsnap-prune-0dGG-SaN)rsyring@loftey:~/projects/tarsnap-prune$

I have other projects where flake8 linting works fine in vscode.

Logs

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

Starting the classic analysis engine.

Linter 'flake8' is not installed. Please install it or select another linter".
Error: Module 'flake8' not installed.

Output from Console under the Developer Tools panel (toggle Developer Tools on under Help)

log.ts:159  INFO no standard startup: not using cached data
TMSyntax.ts:44 Overwriting grammar scope name to file mapping for scope source.jinja.
Old grammar file: /data/rsyring/.vscode/extensions/korekontrol.saltstack-0.0.5/syntaxes/jinja.json.
New grammar file: /data/rsyring/.vscode/extensions/wholroyd.jinja-0.0.8/syntaxes/jinja.json
e.register @ TMSyntax.ts:44
TMSyntax.ts:44 Overwriting grammar scope name to file mapping for scope text.yaml.jinja.
Old grammar file: /data/rsyring/.vscode/extensions/korekontrol.saltstack-0.0.5/syntaxes/sls.json.
New grammar file: /data/rsyring/.vscode/extensions/wholroyd.jinja-0.0.8/syntaxes/jinja-yaml.json
e.register @ TMSyntax.ts:44
webviewElement.ts:132 [Embedded Page] Blocked script execution in 'data:text/html;charset=utf-8,%3C%21DOCTYPE%20html%3E%0D%0A%3Chtml%20lang%3D%22en%22%20style%3D%22width%3A%20100%25%3B%20height%3A%20100%25%22%3E%0D%0A%3Chead%3E%0D%0A%09%3Ctitle%3EVirtual%20Document%3C%2Ftitle%3E%0D%0A%3C%2Fhead%3E%0D%0A%3Cbody%20style%3D%22margin%3A%200%3B%20overflow%3A%20hidden%3B%20width%3A%20100%25%3B%20height%3A%20100%25%22%3E%0D%0A%3C%2Fbody%3E%0D%0A%3C%2Fhtml%3E' because the document's frame is sandboxed and the 'allow-scripts' permission is not set.
console.ts:136 [Extension Host] vscode-icons is active!
console.ts:136 [Extension Host] Python Extension: Linter 'flake8' is not installed. Please install it or select another linter". Error: Module 'flake8' not installed.
	at PythonExecutionService.<anonymous> (/data/rsyring/.vscode/extensions/ms-python.python-2018.5.0/out/client/common/process/pythonProcess.js:96:27)
	at Generator.next (<anonymous>)
	at fulfilled (/data/rsyring/.vscode/extensions/ms-python.python-2018.5.0/out/client/common/process/pythonProcess.js:12:58)
	at <anonymous>
t.log @ console.ts:136
notificationsAlerts.ts:42 Linter flake8 is not installed.
e.onDidNotificationChange @ notificationsAlerts.ts:42

[rsyring]

Well, I had deleted and reinstalled the virtualenv so I had to re-install flake8. Once I did so, I have:

$ /data/tmp/virtualenvs/tarsnap-prune-src-eTYfY8x1/bin/python -m flake8 --version
3.5.0 (mccabe: 0.6.1, pycodestyle: 2.3.1, pyflakes: 1.6.0) CPython 3.6.5 on Linux

And…amazingly?, I no longer have the problem with VS Code. I’m certain I tried that same workflow a couple times before I reported the issue and you can see in my terminal paste above that from inside VS Code, flake8 was installed. But…who knows, it’s working now. Sorry to waste your time. 😮/

[DonJayamanne]

• Please could you provide the output from the following command in your terminal: /data/tmp/virtualenvs/tarsnap-prune-src-eTYfY8x1/bin/python -m flake8 --version

• Please confirm you have restarted VS Code after making the changes to the settings.json file.