ERROR: Could not find a version that satisfies the requirement os code example

Example 1: pip error could not find a version that satisfies the requirement

$ curl https://pypi.org

The requestors Network has been blacklisted due to excessive request volume. 
If you are a hosting customer, please contact your hosting company's support. 
If you are the hosting company, please contact infrastructure-staff@python.org to resolve

Example 2: linux Could not find a version that satisfies the requirement

#instead of requirements.txt use
python3 -m pip install <pkg>
# Some packages just want your personal attention...