Add example of calling Python modules from Boost.Build.

[SVN r34474]

v2/example/python_modules/Jamroot

@@ -0,0 +1,5 @@
+
+import python_helpers ;
+
+ECHO "test1:" [ python_helpers.test1 ] ;
+ECHO "test2:" [ python_helpers.test2 1234 : 5678 ] ;

v2/example/python_modules/python_helpers.jam

@@ -0,0 +1,7 @@
+
+# Import the Python rules to Boost.Build
+PYTHON_IMPORT_RULE python_helpers : test1 : python_helpers : test1 ;
+PYTHON_IMPORT_RULE python_helpers : test2 : python_helpers : test2 ;
+
+# Make the new rules accessible to everybody who imports us.
+EXPORT python_helpers : test1 test2 ;

v2/example/python_modules/python_helpers.py

@@ -0,0 +1,15 @@
+
+# Declare a couple of functions called from Boost.Build
+#
+# Each function will receive as many arguments as there ":"-separated
+# arguments in bjam call. Each argument is a list of strings.
+# As a special exception (aka bug), if no arguments are passed in bjam,
+# Python function will be passed a single empty list.
+#
+# All Python functions must return a list of strings, which may be empty.
+
+def test1(l):
+    return ["foo", "bar"]
+    
+def test2(l, l2):
+    return [l[0], l2[0]]

v2/example/python_modules/readme.txt

@@ -0,0 +1,11 @@
+
+This example shows how you can use Python modules from Boost.Build.
+
+In order to do this, you need to build bjam with Python support, by running:
+
+   ./build.sh --with-python=/usr
+   
+in jam directory. (Replace /usr with the root of your Python installation.)
+
+The integration between Python and bjam is very basic now, but enough to
+be useful.