Why does static version of the Boost Python library has a dependency to Python in Windows?

I'm developing a Python binding for a C++ library using Boost Python. To avoid having issues distributing the Boost libraries, I'm using the static versions. It works fine in Linux and MacOSX, but in Windows, a dependency to Python is still required. My CMakeLists.txt is set as:

if((${CMAKE_SYSTEM_NAME} STREQUAL "Linux") OR APPLE)
     target_link_libraries(my_python_module ${Boost_LIBRARIES})
elseif(WIN32 AND MSVC)
    add_definitions(/DBOOST_PYTHON_STATIC_LIB) # This is also required to force the usage of libboost_python37-vc141-mt-x64-1_70.lib instead of boost_python37-vc141-mt-x64-1_70.lib
    target_link_libraries(my_python_module ${Boost_LIBRARIES}) # This includes the Boost Python library
    # Even though Boost Python library is included statically, in Windows it has a dependency to the Python library.
    target_link_libraries(my_python_module ${Python_LIBRARIES})
endif()

Thus because in Windows, if I remove the target_link_libraries(my_python_module ${Python_LIBRARIES}) line, I get a:

LINK : fatal error LNK1104: Can't open file 'python37.lib'

My resulting DLL has indeed Python as a dependency:

C:\PythonModule\bin\Release\Release>"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\Hostx64\x64\dumpbin.exe" /DEPENDENTS my_python_module.dll
Microsoft (R) COFF/PE Dumper Version 14.16.27031.1
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file my_python_module.dll

File Type: DLL

  Image has the following dependencies:

    python37.dll <------- HERE
    MSVCP140.dll
    VCRUNTIME140.dll
    api-ms-win-crt-runtime-l1-1-0.dll
    api-ms-win-crt-heap-l1-1-0.dll
    KERNEL32.dll

  Summary

        B000 .data
        3000 .pdata
       18000 .rdata
        1000 .reloc
        1000 .rsrc
       27000 .text

Since I'm using Boost static libraries, the process is linking against libboost_python37-vc141-mt-x64-1_70.lib, not boost_python37-vc141-mt-x64-1_70.lib (which is the library module associated to the dynamic library, boost_python37-vc141-mt-x64-1_70.dll). I can check this on the command line passed to Visual Studio (thanks to -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON):

Link:
  C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX86\x64\link.exe /ERRORREPORT:QUEUE /OUT:"C:\PythonModule\bin\Release\Release\my_python_module.dll" /INCREMENTAL:NO /NOLOGO "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_filesystem-vc141-mt-x64-1_70.lib"
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_program_options-vc141-mt-x64-1_70.lib"
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_python37-vc141-mt-x64-1_70.lib"  <------- HERE
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_thread-vc141-mt-x64-1_70.lib"
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_system-vc141-mt-x64-1_70.lib"
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_stacktrace_windbg-vc141-mt-x64-1_70.lib"
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_chrono-vc141-mt-x64-1_70.lib"
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_date_time-vc141-mt-x64-1_70.lib"
  "C:\local\boost_1_70_0\lib64-msvc-14.1\libboost_atomic-vc141-mt-x64-1_70.lib"
  "C:\Program Files\Python37\libs\python37.lib"
  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /manifest:embed /PDB:"C:/PythonModule/lib/Release/Release/my_python_module.pdb" /SUBSYSTEM:CONSOLE /TLBID:1 /DYNAMICBASE /NXCOMPAT /IMPLIB:"C:/PythonModule/lib/Release/Release/my_python_module.lib" /MACHINE:X64  /machine:x64 /IGNORE:4049,4217 /DLL my_python_module.dir\Release\my_python_module.obj
     Creating library C:/PythonModule/lib/Release/Release/my_python_module.lib and object C:/PythonModule/lib/Release/Release/my_python_module.exp
  my_python_module.vcxproj -> C:\PythonModule\bin\Release\Release\my_python_module.dll

BTW, these are the Boost officially provided binaries, by the way, obtained from https://dl.bintray.com/boostorg/release/1.70.0/binaries/boost_1_70_0-msvc-14.1-64.exe

The static Boost Python library DOESN'T have a dependency to Python, as far as I can check:

C:\local\boost_1_70_0\lib64-msvc-14.1>"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\Hostx64\x64\dumpbin.exe" /DEPENDENTS libboost_python37-vc141-mt-x64-1_70.lib
Microsoft (R) COFF/PE Dumper Version 14.16.27031.1
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file libboost_python37-vc141-mt-x64-1_70.lib

File Type: LIBRARY

  Summary

         100 .CRT$XCU
         35A .bss
       17EF8 .chks64
         DD0 .data
         CFE .data$r
        1804 .debug$S
        23B5 .drectve
        5B20 .pdata
        9FD3 .rdata
         EF8 .rdata$r
         4DB .text$di
       32D89 .text$mn
        3F59 .text$x
         608 .text$yd
       11C10 .xdata
         4C0 .xdata$x

While the shared one does:

C:\local\boost_1_70_0\lib64-msvc-14.1>"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\Hostx64\x64\dumpbin.exe" /DEPENDENTS boost_python37-vc141-mt-x64-1_70.dll
Microsoft (R) COFF/PE Dumper Version 14.16.27031.1
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file boost_python37-vc141-mt-x64-1_70.dll

File Type: DLL

  Image has the following dependencies:

    python37.dll <------- HERE
    MSVCP140.dll
    KERNEL32.dll
    VCRUNTIME140.dll
    api-ms-win-crt-runtime-l1-1-0.dll
    api-ms-win-crt-heap-l1-1-0.dll

  Summary

        3000 .data
        3000 .pdata
       18000 .rdata
        1000 .reloc
        1000 .rsrc
       1D000 .text

So, my main question is:

Why, if I'm using the static version of the Boost Python library, I still have that Python dependency?

I'm not using Python directly in the module in any other way, and in Linux, such dependency doesn't exist.

Thanks a lot for your help.

Recommended topics

Hot tags