I wonder whether anyone from the Boost.Build project would be able to comment, and can explain the error message.
It's true I relatively recently added https://github.com/boostorg/python/commit/d4d41d94aecc9f8098aabd3587fcb95458451f71, but I don't see how this could cause the observed error (which doesn't seem to be about a failed Python detection, but about an internal Boost.Build error (to detect the `python.python_for_extensions` rule).

I can't reproduce the problem myself. From the generated output it seems as if passing `--without-python` would suppress the failure, but that hadn't been necessary before, or has it ?


On 11.03.2018 05:08, Olaf van der Spek via Boost wrote:
On Sat, Mar 10, 2018 at 8:57 PM, Daniel James via Boost
<boost@lists.boost.org> wrote:
As always, the release managers would appreciate it if you download
the candidate of your choice and give building it a try. Please report
both success and failure, and anything else that is noteworthy.
Windows 7 x64; MSVC 15.6.1; normal cmd prompt:

libs\log\build\Jamfile.v2:45: Unescaped special character in argument
libs\python\Jamfile:49: Unescaped special character in argument [*\/:."']
C:/VC/boost/libs/predef/check/../tools/check\predef.jam:46: Unescaped
special character in argument $(language)::$(expression)
Performing configuration checks

    - default address-model    : 32-bit
    - default architecture     : x86

Building the Boost C++ Libraries.

    - symlinks supported       : yes
    - C++11 mutex              : yes
    - Boost.Config Feature Check: cxx11_auto_declarations : yes
    - Boost.Config Feature Check: cxx11_constexpr : yes
    - Boost.Config Feature Check: cxx11_defaulted_functions : yes
    - Boost.Config Feature Check: cxx11_final : yes
    - Boost.Config Feature Check: cxx11_hdr_mutex : yes
    - Boost.Config Feature Check: cxx11_hdr_regex : yes
    - Boost.Config Feature Check: cxx11_hdr_tuple : yes
    - Boost.Config Feature Check: cxx11_lambdas : yes
    - Boost.Config Feature Check: cxx11_noexcept : yes
    - Boost.Config Feature Check: cxx11_nullptr : yes
    - Boost.Config Feature Check: cxx11_rvalue_references : yes
    - Boost.Config Feature Check: cxx11_template_aliases : yes
    - Boost.Config Feature Check: cxx11_thread_local : yes
    - Boost.Config Feature Check: cxx11_variadic_templates : yes
    - has_icu builds           : no
warning: Graph library does not contain MPI-based parallel components.
note: to enable them, add "using mpi ;" to your user-config.jam
    - zlib                     : no
    - bzip2                    : no
    - lzma                     : no
    - iconv (libc)             : no
    - iconv (separate)         : no
    - icu                      : no
    - icu (lib64)              : no
    - native-atomic-int32-supported : yes
    - message-compiler         : yes
    - native-syslog-supported  : no
    - pthread-supports-robust-mutexes : no
    - compiler-supports-visibility : no
    - compiler-supports-ssse3  : yes
    - compiler-supports-avx2   : yes
    - gcc visibility           : no
    - long double support      : yes
warning: skipping optional Message Passing Interface (MPI) library.
note: to enable MPI support, add "using mpi ;" to user-config.jam.
note: to suppress this message, pass "--without-mpi" to bjam.
note: otherwise, you can safely ignore this message.
warning: No python installation configured and autoconfiguration
note: failed.  See http://www.boost.org/libs/python/doc/building.html
note: for configuration instructions or pass --without-python to
note: suppress this message and silently skip all Boost.Python targets
error: at C:/VC/boost/tools/build/src/kernel\modules.jam:107
error: Unable to find file or target named
error:     'python_for_extensions'
error: referred to from project at
error:     ''

Is Python enabled by default?


      ...ich hab' noch einen Koffer in Berlin...