Add Python formatting CMake targets (black, flake8)

.flake8

@@ -0,0 +1,6 @@
+# Minimal flake8 tweak to be compatible with black's line length of 88 characters
+# https://black.readthedocs.io/en/stable/the_black_code_style.html#line-length
+
+[flake8]
+max-line-length = 88
+extend-ignore = E203

CMakeLists.txt

@@ -102,3 +102,6 @@ add_subdirectory(python)
 
 #--- create uninstall target ---------------------------------------------------
 include(cmake/EDM4HEPUninstall.cmake)
+
+#--- code format targets -------------------------------------------------------
+include(cmake/pythonFormat.cmake)

cmake/pythonFormat.cmake

@@ -0,0 +1,35 @@
+# Additional target to run python linters and formatters on python scripts
+#
+# Requires black/flake8 to be available in the environment
+
+
+# Get all our Python files
+file(GLOB_RECURSE ALL_PYTHON_FILES ${PROJECT_SOURCE_DIR}/python/*.py 
+  ${PROJECT_SOURCE_DIR}/scripts/*.py ${PROJECT_SOURCE_DIR}/test/*.py)
+
+# Black is rather simple because there are no options...
+find_program(BLACK_EXECUTABLE black)
+if(BLACK_EXECUTABLE)
+    add_custom_target(
+            black
+            COMMAND ${BLACK_EXECUTABLE}
+            ${ALL_PYTHON_FILES}
+    )
+    set_target_properties(black PROPERTIES EXCLUDE_FROM_ALL TRUE)
+else()
+    message(STATUS "Failed to find black executable - no target to run black can be set")
+endif()
+
+find_program(FLAKE8_EXECUTABLE flake8)
+if(FLAKE8_EXECUTABLE)
+    add_custom_target(
+        flake8
+        COMMAND ${FLAKE8_EXECUTABLE}
+        --config=${PROJECT_SOURCE_DIR}/.flake8
+        ${ALL_PYTHON_FILES}
+    )
+    set_target_properties(flake8 PROPERTIES EXCLUDE_FROM_ALL TRUE)
+else()
+    message(STATUS "Failed to find flake8 executable - no target to run flake8 can be set")
+endif()
+