This question already has an answer here:
Importing installed package from script raises “AttributeError: module has no attribute” or “ImportError: cannot import name”
I don't see your file structure, so I can't be sure, but if you have a file called
flask.py in the same folder, python will import it instead of the Flask module
I think this is the answer:
/_workspace/py/flask python helloworld.py
use underscope '_' in names, python thinks you want to import flask from you 'flask python helloworld'.