Add python discovery

BUILD.md

@@ -9,6 +9,7 @@
 
 - [cmake](https://cmake.org/download/):  3.9
 - [Qt](https://www.qt.io/download-open-source):   5.10.1
+- [Python](https://www.python.org/downloads/): 3.6 or higher
 - [OpenSSL](https://www.openssl.org/): Use the latest available 1.0 version (**NOT** 1.1) of OpenSSL to avoid security vulnerabilities.
 - [VHACD](https://github.com/virneo/v-hacd)(clone this repository)(Optional)
 

BUILD_LINUX.md

@@ -40,6 +40,11 @@ Install build tools:
 sudo apt-get install cmake
 ```
 
+Install Python 3:
+```bash
+sudo apt-get install python3.6
+```
+
 
 ### Get code and checkout the tag you need
 

BUILD_OSX.md

@@ -6,6 +6,10 @@ Please read the [general build guide](BUILD.md) for information on dependencies
 
     brew install cmake openssl qt
 
+### Python 3
+
+Download an install Python 3.6.6 or higher from [here](https://www.python.org/downloads/).  Execute the `Update Shell Profile.command` script that is provided with the installer.
+
 ### OpenSSL
 
 Assuming you've installed OpenSSL using the homebrew instructions above, you'll need to set OPENSSL_ROOT_DIR so CMake can find your installations.
@@ -28,7 +32,9 @@ Note that this uses the version from the homebrew formula at the time of this wr
 
 If Xcode is your editor of choice, you can ask CMake to generate Xcode project files instead of Unix Makefiles.
 
-    cmake .. -GXcode
+    cmake .. -G Xcode
+
+If `cmake` complains about Python 3 being missing, you may need to update your CMake binary with command `brew upgrade cmake`, or by downloading and running the latest CMake installer, depending on how you originally instaled CMake 
 
 After running cmake, you will have the make files or Xcode project file necessary to build all of the components. Open the hifi.xcodeproj file, choose ALL_BUILD from the Product > Scheme menu (or target drop down), and click Run.
 

BUILD_WIN.md

@@ -5,11 +5,17 @@ Note: We are now using Visual Studio 2017 and Qt 5.10.1. If you are upgrading fr
 
 Note: The prerequisites will require about 10 GB of space on your drive. You will also need a system with at least 8GB of main memory.
 
-### Step 1. Visual Studio 2017
+### Step 1. Visual Studio 2017 & Python
 
 If you don’t have Community or Professional edition of Visual Studio 2017, download [Visual Studio Community 2017](https://www.visualstudio.com/downloads/).
 
-When selecting components, check "Desktop development with C++." Also on the right on the Summary toolbar, check "Windows 8.1 SDK and UCRT SDK" and "VC++ 2015.3 v140 toolset (x86,x64)".
+When selecting components, check "Desktop development with C++".  Also on the right on the Summary toolbar, check "Windows 8.1 SDK and UCRT SDK" and "VC++ 2015.3 v140 toolset (x86,x64)".  If you do not already have a python development environment installed, also check  "Python Development" in this screen.
+
+If you already have Visual Studio installed and need to add python, open the "Add or remove programs" control panel and find the "Microsoft Visual Studio Installer".  Select it and click "Modify".  In the installer, select "Modify" again, then check "Python Development" and allow the installer to apply the changes.
+
+### Step 1a.  Alternate Python
+
+If you do not wish to use the Python installation bundled with Visual Studio, you can download the installer from [here](https://www.python.org/downloads/).  Ensure you get version 3.6.6 or higher.
 
 ### Step 2. Installing CMake
 

cmake/macros/TargetPython.cmake

@@ -0,0 +1,22 @@
+macro(TARGET_PYTHON)
+    if (NOT HIFI_PYTHON_EXEC)
+        # Find the python interpreter
+        if (CAME_VERSION VERSION_LESS 3.12)
+            # this logic is deprecated in CMake after 3.12
+            # FIXME eventually we should make 3.12 the min cmake verion and just use the Python3 find_package path
+            set(Python_ADDITIONAL_VERSIONS 3)
+            find_package(PythonInterp)
+            set(HIFI_PYTHON_VERSION ${PYTHON_VERSION_STRING})
+            set(HIFI_PYTHON_EXEC ${PYTHON_EXECUTABLE})
+        else()
+            # the new hotness
+            find_package(Python3)
+            set(HIFI_PYTHON_VERSION ${Python3_VERSION})
+            set(HIFI_PYTHON_EXEC ${Python3_EXECUTABLE})
+        endif()
+
+        if ((NOT HIFI_PYTHON_EXEC) OR (HIFI_PYTHON_VERSION VERSION_LESS 3.6))
+            message(FATAL_ERROR "Unable to locate Python interpreter 3.6 or higher")
+        endif()
+    endif()
+endmacro()