Could not find a version that satisfies the requirement flask-restfull (from versions:)

Question

I use windows vista, Python 3.7.3, pip 19.2.1.

I've installed flask with the command "pip install flask". and it's working fine. I make simple flask app. all is ok.

But, I want to code a small restfull Apii with flask-restfull. (https://flask-restful.readthedocs.io/en/latest/installation.html).

I use "pip install flask_restfull", it seems to be ok. But, when I enter in Python interactive mode to test, if "flask_restful" is correctly installed:

>>> import flask_restful
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'flask_restful'

I don't find an issue for this problem. I read all other similar case in stack overflow.

I try "pip freeze"
aniso8601==7.0.0
Click==7.0
Flask==1.1.1
Flask-RESTful==0.3.7
itsdangerous==1.1.0
Jinja2==2.10.1
MarkupSafe==1.1.1
pytz==2019.1
six==1.12.0
Werkzeug==0.15.5

windows vista, Python 3.7.3, pip 19.2.1

Could not find a version that satisfies the requirement flask-restfull (from versions: ) No matching distribution found for flask-restfull.

How do I solve the problem?