Many packages for example on version 3.4 would run on 3.6 just fine, but if there are no distributions for specific platform, they can't be installed, but there is workaround. In .whl files (known as wheels) naming convention decide whether you can install package on specified platform. Eg. scikit_learn‑0.18.1‑cp36‑cp36m‑win_amd64.whl
[package_name]-[version]-[python interpreter]-[python-interpreter]-[Operating System].whl. If name of wheel file is changed, so platform does match, pip tries to install package even if platform or python version does not match. Removing platform or interpreter from name will rise an error in newest versoin of pip module kjhfkjdf.whl is not a valid wheel filename.
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Alternativly .whl file can be unpacked using an archiver as 7-zip. - It usually contains distribution meta folder and folder with source files. These source files can be simply unpacked to site-packges
directory unless this wheel contain installation script, if so, it has to be run first.