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Many, pure python, packages are not yet available on the Python Package Index as wheels but still install fine. However, some packages on Windows give the dreaded vcvarsall.bat not found error.
The problem is that the package that you are trying to install contains a C or C++ extension and is not currently available as a pre-built wheel from the python package index, pypi, and on windows you do not have the tool chain needed to build such items.
The simplest answer is to go to Christoph Gohlke’s excellent site and locate the appropriate version of the libraries that you need. By appropriate in the package name a -cpNN- has to match your version of python, i.e. if you are using windows 32 bit python even on win64 the name must include -win32- and if using the 64 bit python it must include -win_amd64- and then the python version must match, i.e. for Python 34 the filename must include -cp34-, etc. this is basically the magic that pip does for you on the pypi site.
Alternatively, you need to get the appropriate windows development kit for the version of python that you are using, the headers for any library that the package you are trying to build interfaces to, possibly the python headers for the version of python, etc.
Python 2.7 used Visual Studio 2008, Python 3.3 and 3.4 used Visual Studio 2010, and Python 3.5+ uses Visual Studio 2015.
Then you may need to locate the header files, at the matching revision for any libraries that your desired package links to and download those to an appropriate locations.
Finally you can let pip do your build - of course if the package has dependencies that you don’t yet have you may also need to find the header files for them as well.
Alternatives: It is also worth looking out, both on pypi or Christop’s site, for any slightly earlier version of the package that you are looking for that is either pure python or pre-built for your platform and python version and possibly using those, if found, until your package does become available. Likewise if you are using the very latest version of python you may find that it takes the package maintainers a little time to catch up so for projects that really need a specific package you may have to use a slightly older python for the moment. You can also check the packages source site to see if there is a forked version that is available pre-built or as pure python and searching for alternative packages that provide the functionality that you require but are available - one example that springs to mind is the Pillow, actively maintained, drop in replacement for PIL currently not updated in 6 years and not available for python 3.
Afterword, I would encourage anybody who is having this problem to go to the bug tracker for the package and add to, or raise if there isn’t one already, a ticket politely requesting that the package maintainers provide a wheel on pypi for your specific combination of platform and python, if this is done then normally things will get better with time, some package maintainers don’t realise that they have missed a given combination that people may be using.
Pip follows the rules of Semantic Versioning and by default prefers released packages over pre-releases. So if a given package has been released as V0.98 and there is also a release candidate V1.0-rc1 the default behaviour of pip install will be to install V0.98 - if you wish to install the release candidate, you are advised to test in a virtual environment first, you can enable do so with --pip install --pre package-name or --pip install --pre --upgrade package-name. In many cases pre-releases or release candidates may not have wheels built for all platform & version combinations so you are more likely to encounter the issues above.
You can also use pip to install development versions of packages from github and other locations, since such code is in flux it is very unlikely to have wheels built for it, so any impure packages will require the presence of the build tools, and they may be broken at any time so the user is strongly encouraged to only install such packages in a virtual environment.
Three options exist for such installations:
pip install path/to/downloaded/file note that for most compression formats pip will handle unpacking to a cache area, etc.pip install URL/of/package/repository - you may also need to use the --trusted-host, --client-cert and/or --proxy flags for this to work correctly, especially in a corporate environment. e.g: