Pip install from pypi works, but from testpypi fails (cannot find requirements)

Update

PyPI has upgraded its site. According to the docs, the new advice is:

pip install --index-url https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple poirot

• --index-url points to your package on TestPyPI.
• --extra-index-url points to dependencies on PyPI.
• poirot is your package.

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Out-dated

Try pip install --extra-index-url https://testpypi.python.org/pypi poirot.

See also a reference post.

Trying in Jan 2021, the update in the accepted answer didn't work for me. This worked:

pip install -i https://test.pypi.org/pypi/ --extra-index-url https://pypi.org/simple <your_package_in_testpypi>

Note that the first URL is test.pypi.org/pypi, and the second is pypi.org/simple.

Their official page should be updated, its instruction shows:

pip install -i https://test.pypi.org/simple/ <your_package_in_testpypi>

which does not work.