SCons release 4.0.0 now available from the download page at SourceForge.

This release ONLY supports Python versions 3.5+.


If you have an existing pip-installed version of SCons on Windows, you can avoid some reported issues by uninstalling SCons first, an upgrade install may not work correctly:

pip uninstall SCons

Here is a summary of the changes since 3.1.2:


  • Added support for scanning multiple entries in an action string if IMPLICIT_COMMAND_DEPENDENCIES is set to 2 or 'all'. This enables more thorough action scanning where every item in each command line is scanned to determine if it is a non-source and non-target path and added to the list of implicit dependencies for the target.
  • Added new module SCons.Scanner.Python to allow scanning .py files.
  • Added support for explicitly passing a name when creating Value() nodes. This may be useful when the value can't be converted to a string or if having a name is otherwise desirable.
  • Added a new flag called "linedraw" for the command line argument "--tree" that instructs scons to use single line drawing characters to draw the dependency tree.
  • Add CompilationDatabase() builder in compilation_db tool. Contributed by MongoDB. Setting COMPILATIONDB_USE_ABSPATH to True|False controls whether the files are absolute or relative paths. Address Issue #3693 and #3694 found during development.
  • Extended Environment.Dump() to select a format to serialize construction variables (pretty, json).
  • New conditional C Scanner (SCons.Scanner.C.CConditionalScanner()) which interprets C/C Preprocessor conditional syntax (#ifdef, #if, #else, #elif, #define, etc.)
  • Experimental New Feature: Enable caching MSVC configuration If SCONS_CACHE_MSVC_CONFIG shell environment variable is set, SCons will cache the results of past calls to vcvarsall.bat to a file; integrates with existing memoizing of such vars.
  • Preliminary Python 3.9 support.


  • Drop support for Python 2.7. SCons will be Python 3.5+ going forward.
  • Remove deprecated SourceCode()


  • Resolve Issue #3248 - Removing -Wl,-Bsymbolic from SHLIBVERSIONFLAGS


    If your build depends on the above you must now add to your SHLIBVERSIONFLAGS

  • Added check for SONAME in environment to setup symlinks correctly (Github Issue #3246)

  • Microsoft Visual Studio switch to using uuid module to generate GUIDs rather than hand rolled method using md5 directly.


    This change affects the following builders' output. If your build depends on the output of these builders you will likely see a rebuild:

    • Package() (with PACKAGETYPE='msi')
    • MSVSSolution()
    • MSVSProject()
  • Improve Visual Studio solution/project generation code to add support for a per-variant cppflags. Intellisense can be affected by cppflags, this is especially important when it comes to /std:c++* which specifies what C++ standard version to target. SCons will append /Zc:__cplusplus to the project's cppflags when a /std:c++* flag is found as this is required for intellisense to use the C++ standard version from cppflags.

  • Allow user specified location for vswhere.exe specified by VSWHERE.


    This must be set at the time the 'msvc' 'msvs' and/or 'mslink' tool(s) are initialized to have any effect.

  • Fixed Github Issue 3628 - Hardcoding pickle protocol to 4 (supports python 3.4+) and skipping Python 3.8's new pickle protocol 5 whose main advantage is for out-of-band data buffers.

  • MSVC updates: When there are multiple product installations (e.g, Community and Build Tools) of MSVC 2017 or MSVC 2019, an Enterprise, Professional, or Community installation will be selected before a Build Tools installation when "14.1" or "14.2" is requested, respectively. (GH Issue #3699).

  • MSVC updates: When there are multiple product installations of MSVC 2017 (e.g., Community and Express), 2017 Express is no longer returned when "14.1" is requested. Only 2017 Express will be returned when "14.1Exp" is requested. (GH Issue #3699).

  • MSVC updates: pass on VSCMD_DEBUG and VSCMD_SKIP_SENDTELEMETRY to msvc tool setup if set in environment. Add Powershell to default env (used to call telemetry script).

  • Renamed to and left redirecting tool. 'as' is a reserved word and so changing the name was required as we wanted to import symbols for use in compilation_db tool.

  • Add no_progress (-Q) option as a set-able option. However, setting it in the SConstruct/SConscript will still cause "scons: Reading SConscript files ..." to be printed, since the option is not set when the build scripts first get read.

  • Docbook builder provides a fallback if lxml fails to generate a document with tostring().

  • SubstitutionEnvironment and OverrideEnvironment now have keys() and values() methods to better emulate a dict (already had items()).


  • Cleanup dangling symlinks before running builders (Issue #3516)

  • Fixed usage of abspath and path for RootDir objects on Windows. Previously env.fs.Dir("T:").abspath would return "T:\\T:" and now it correctly returns "T:".

  • Fix Issue #3469 - Fixed improper reuse of temporary and compiled files by Configure when changing the order and/or number of tests. This is done by using the hash of the generated temporary files content and (For the target files) the hash of the action. So where previously files would be named:

    • config_1.c, config_1.o, config_1

    they will now be named (For example):

    • conftest_68b375d16e812c43e6d72d6e93401e7c_0.c,
    • conftest_68b375d16e812c43e6d72d6e93401e7c_0_5713f09fc605f46b2ab2f7950455f187.o


    • conftest_68b375d16e812c43e6d72d6e93401e7c_0.o
    • conftest_68b375d16e812c43e6d72d6e93401e7c_0_5713f09fc605f46b2ab2f7950455f187 (for executable)
  • Updated documentation toolchain to work properly under Python3, also removed libxslt support from the Docbook Tool. (issue #3580)

  • Fix broken clang + MSVC 2019 combination by using MSVC configuration logic to propagate VCINSTALLDIR and VCToolsInstallDir which clang tools use to locate header files and libraries from MSVC install. (Fixes GH Issue #3480)

  • Fix Github Issue #2904 - Provide useful error message when more than one Configure Contexts are opened. Only one open is allowed. You must call conf.Finish() to complete the currently open one before creating another


  • Improve performance of Subst by preventing unnecessary frame allocations by no longer defining the *Subber classes inside of their respective function calls.
  • Improve performance of Subst in some cases by preventing unnecessary calls to eval when a token is surrounded in braces but is not a function call.
  • Improve performance of subst by removing unnecessary recursion.


  • Resolve Issue #3451 and Issue #3450 - Rewrite SCons and packaging. Move script logic to entry points so package can create scripts which use the correct version of Python.


  • Significant rework of documentation: API docs are now generated using Sphinx; manpage and user guide now use more "standard" markup elements (which could facilitate later conversion to a different doc format, should that choice be made); significant rewordings in manpage. Manpage Examples moved to an external repository / website.

Thanks to the following contributors listed below for their contributions to this release.

git shortlog --no-merges -ns 3.1.2..HEAD
290  William Deegan
184  Mats Wichmann
46  Adam Gross
22  Daniel Moody
16  Joseph Brill
15  Dirk Baechle
12  Ivan Kravets
9  Mathew Robinson
6  Paul Tipei
1  Rob Boehne
1  Robert Boehne
1  Daniel
1  Andrew Morrow
1  Iosif Daniel Kurazs
1  James Benton
1  Jeremy Elson
1  Konstantin Gonchar
1  Andrii Doroshenko (Xrayez)