Hi Stefan,

Thanks for the advice and the link; they were really helpful.
Just by itself, the line "using python : 3.7 ;" still returned an
error. However, upon reading the link, I could also specify the path
that leads to Python. So, I tried:

using python : 3.7 :
/Library/Frameworks/Python.framework/Versions/3.7/bin/python3.7

Now, even without explicitly saying the python version,

sudo ./b2 install

began to use the right Python version. However, now the compiler
complained about not finding the file pyconfig.h. Looking at the
output, it seems like the build was specifying the following
nonexistent directory as an include path
"/Library/Frameworks/Python.framework/Versions/3.7/include/python3.7/".
Actually, pyconfig.h is located inside
"/Library/Frameworks/Python.framework/Versions/3.7/include/python3.7m/".
Note the extra "m" at the end (I don't know what the m means though).
Anyway, as per the link you sent, I could add another path to the .jam
file to specify an include directory, so the final line was

using python : 3.7 :
"/Library/Frameworks/Python.framework/Versions/3.7/bin/python3.7" :
"/Library/Frameworks/Python.framework/Versions/3.7/include/python3.7m/"

Now it compiled relatively smoothly :)

Now, I tried getting it to work without making a user-specific file. I
looked at the boost folder and saw that inside "project-config.jam",
there was a section that said

if ! [ python.configured ]
{
    using python : 3.7 : "/Library/Frameworks/Python.framework/Versions/3.7"
}

When I ran it just like this, it still failed. However, when I edited
"project-config.jam" to go to the exact python executable (not just
the parent directory), it started working, but this time with the
header problem again.

using python : 3.7 :
"/Library/Frameworks/Python.framework/Versions/3.7/bin/python3.7"

So, I added the whole include line from my user file, and now it worked.

using python : 3.7 :
"/Library/Frameworks/Python.framework/Versions/3.7/bin/python3.7" :
"/Library/Frameworks/Python.framework/Versions/3.7/include/python3.7m/"

Ultimately, my prediction is that there are two problems:
1) The script ./bootstrap.sh, which generates the project-config.jam,
should print the full path to the python3.7 executable instead of just
the parent directory when given a --with-python=[executable] flag.
2) Somewhere in the build process, an include flag is missing an "m"
at the end which specifies the following nonexistent directory as an
include path "/Library/Frameworks/Python.framework/Versions/3.7/include/python3.7/".
This prevents the compiler from finding pyconfig.h, causing an error.
Actually, pyconfig.h is located inside
"/Library/Frameworks/Python.framework/Versions/3.7/include/python3.7m/".

However, I'm not sure if these are specific to the version 3.7, or in general.

You have helped me a lot to get this working, and I hope this
information helps you (or someone else) find (and fix!) some of them.

Thank you very much,
Mortimer

On Mon, Sep 7, 2020 at 2:47 PM Stefan Seefeld <stefan@seefeld.name> wrote: