How to install Python package from source on Windows

[Chris Angelico]

On Tue, May 16, 2017 at 11:19 AM, Deborah Swanson
<python at deborahswanson.net> wrote:
> Chris Angelico wrote, on Monday, May 15, 2017 2:58 PM
>> You seem to be of the opinion that some day, binary
>> executables will be compiled using pure Python code.
>
> Well, my naive opinion is that they should be. But it was just one
> message back that I learned some Python built-in modules are at least
> partially written in C. I didn't know that, nor did I know or suspect
> that installation files for official Python releases likely contained C
> compilers. This raises a lot of questions for me, though it probably
> would be better for me to read and think about them on my own before
> coming back here with anything.

It is possible to build a compiler for Python in Python. (See: PyPy.)
The most normal way to build extension libraries is with C, though,
because that's what most lower-level libraries depend on. For example,
suppose you want to build a GUI toolkit for Python, using the GTK
library. You can't easily do that in Python (technically you *can*,
using ctypes, but ctypes is itself implemented in C), so you'll end up
writing a C extension library.

> I'll accept that, though I still don't quite understand the recent
> dependence on Visual C++, after Python has been building its releases
> with the tools you and others mention from the beginning until shortly
> after the first 3 build was released, and the requirement has been so
> much deeper since 3.4.3, that Python (apparently) can no longer use the
> Visual C++ compiler built into XP.  These are just things I wonder about
> since these new requirements put a real crimp in what I'm currently able
> to do, and I wonder how they will change Linux too. Again, lots of stuff
> for me to pursue on my own here.

An installed Python does not itself depend on MSVC. It's only when you
need to compile additional C code - another Python module that is
implemented in C - and you can't pick up someone else's precompiled
version. It's not a new requirement; although you could perhaps argue
that pip's presence in the standard library has made this a lot more
likely to come up, as previously, you wouldn't have been able to
install this module *at all* without fiddling around manually.

> No, with what I've learned today, I certainly would agree that Python
> has its beholdens, and likely always will.  The bright side is that
> Python at least doesn't appear to be unduly constrained in how it uses
> the C/C++ code it does. I just hope that it continues to be kept to a
> minimum, but I guess I'm just a stinking purist about some things.

Actually, I'm glad that most of Python's core is implemented in C,
because it means my code runs faster :) It's all thoroughly
unit-tested, and I'm happy with it.

ChrisA