Running locally with GAE Python second generation - google-app-engine

Question

I've been using GAE/P 1st gen for many years and am making the jump to my first GAE/P 2nd gen project.
I'm trying to run it locally like I did with dev_appserver.py for 1st gen apps, but the docs are very confusing in this respect.
I can run Flask on its own (python main.py) but static files don't work (since Flask knows nothing about app.yaml) and the datastore won't work either.
The GAE docs say that dev_appserver.py should work for 2nd gen (except on Windows but I'm on Mac) but when I run it, I get the error below.
This happens when I run dev_appserver.py with Python 2 or 3. I've also set CLOUDSDK_PYTHON to my Python 2 binary as instructed.
So how the heck can I run my GAE/P 2nd gen project locally in way that static files and the datastore work?!?
$ python ~/google-cloud-sdk/bin/dev_appserver.py --application=myapp --support_datastore_emulator=False ./app.yaml
INFO 2019-02-12 00:39:21,885 devappserver2.py:278] Skipping SDK update check.
INFO 2019-02-12 00:39:23,128 api_server.py:275] Starting API server at: http://localhost:51187
INFO 2019-02-12 00:39:23,139 instance_factory.py:71] Detected Python 3.6.5
INFO 2019-02-12 00:39:24,459 instance_factory.py:205] Using pip to install dependency libraries; pip stdout is redirected to /var/folders/yd/xr84fg0946l72fp_cc6j9l540000gr/T/tmpj3SEUZ
INFO 2019-02-12 00:39:24,459 instance_factory.py:211] Running /var/folders/yd/xr84fg0946l72fp_cc6j9l540000gr/T/tmpLtysT3/bin/pip install --upgrade pip
INFO 2019-02-12 00:39:24,469 stub_util.py:357] Applying all pending transactions and saving the datastore
INFO 2019-02-12 00:39:24,469 stub_util.py:360] Saving search indexes
Traceback (most recent call last):
File "/.../google-cloud-sdk/platform/google_appengine/dev_appserver.py", line 96, in <module>
_run_file(__file__, globals())
File "/.../google-cloud-sdk/platform/google_appengine/dev_appserver.py", line 90, in _run_file
execfile(_PATHS.script_file(script_name), globals_)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/devappserver2.py", line 600, in <module>
main()
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/devappserver2.py", line 588, in main
dev_server.start(options)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/devappserver2.py", line 360, in start
options.api_host, apiserver.port, wsgi_request_info_)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/dispatcher.py", line 248, in start
ssl_port)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/dispatcher.py", line 384, in _create_module
ssl_port=ssl_port)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/module.py", line 1309, in __init__
super(AutoScalingModule, self).__init__(**kwargs)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/module.py", line 598, in __init__
self._module_configuration)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/module.py", line 231, in _create_instance_factory
module_configuration=module_configuration)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/python/instance_factory.py", line 98, in __init__
self._SetupVirtualenvFromConfiguration()
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/python/instance_factory.py", line 143, in _SetupVirtualenvFromConfiguration
self._venv_dir, requirements_file.name)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/python/instance_factory.py", line 228, in _SetupVirtualenv
cls._RunPipInstall(venv_dir, requirements_file_name)
File "/.../google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/python/instance_factory.py", line 212, in _RunPipInstall
pip_proc = subprocess.Popen(pip_cmd, stdout=pip_out)
File "/usr/local/Cellar/python#2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 394, in __init__
errread, errwrite)
File "/usr/local/Cellar/python#2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 1047, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory

Answer 1

After a good night's sleep, I was able to figure out the problem...
I was running dev_appserver.py from within my virtual environment. For some reason, this prevented dev_appserver.py from being able to find pip (needed to install the packages in my requirements.txt).
Exiting my virtual environment before running dev_appserver.py fixed the problem.