Unable to install latest version of a package via pip from PyPI

[Iwo Herka]

Hello,

I do not wish to bother you with boring installation problems; however,
I would be obliged if someone could spare a minute or two to take a look at
my problem.

I've recently uploaded a package on PyPI: pypi.org/project/sexpr/. Latest
version is 0.1.6 (for Python 3+). Unfortunately, I cannot install it via pip:

    $ pip install sexpr==0.1.6

    Could not find a version that satisfies the requirement sexpr==0.1.6 (from
    versions: 0.1.6.linux-x86_64, 0.1.2, 0.1.3, 0.1.4, 0.1.5)
    No matching distribution found for sexpr==0.1.6

However, package is obviously there:

    $ pip search sexpr
    sexpr (0.1.6)  - S-expression toolkit for Python
    INSTALLED: 0.1.5
    LATEST:    0.1.6

Package was compiled and uploaded in a standard way:

    $ python3 setup.py sdist bdist_wheel
    ...
    $ twine upload dist/*
    ...

setuptools version is 39.0.1. twine version is 1.11.0. wheel version is 0.31.1.
I've tried installing with pip version 8.1.1 and 9.0.1. I'm also able to
install the package directly from GitHub without problems. setup.py install
works too. I'm using venv and pyenv.

Am I missing something obvious? Thank you.

Iwo Herka