[Python] Support backend and mem type config for python package

Author: EgorOrachyov

README.md

@@ -223,6 +223,21 @@ $ python3 -m unittest discover -v
 inside the build directory in the folder with python wrapper `python/pycubool/`. 
 So, the wrapper will be able to automatically locate required lib file.
 
+### Python package runtime config
+
+**Pycubool** Python-package can be configured before import by the following environment variables: 
+
+- `CUBOOL_PATH` - custom path to compiled cubool library object. 
+Without that variable by default the package will try to find library in the package folder.
+
+- `CUBOOL_BACKEND` - allows to select backend for execution. 
+By default library selects cuda if present. Pass value `cpu` to force cpu computations,
+even if cuda backend is presented and supported for selection.
+
+- `CUBOOL_MEM` - type of the memory to use if run computations in cuda backend.
+By default library uses device memory. If pass in the variable value `managed`, then
+backend will be configured to use cuda managed memory for resources allocation.
+
 ## Usage 
 
 The following C++ code snipped demonstrates, how library functions and

cubool/sources/core/library.cpp

@@ -278,7 +278,7 @@ namespace cubool {
                    << " sharedMemoryPerBlockKiBs: " << caps.sharedMemoryPerBlockKiBs;
         }
         else {
-            stream << "Cuda device is not presented";
+            stream << "Cuda device is not presented (fallback to cpu backend)";
         }
 
         stream << LogStream::cmt;

python/pycubool/wrapper.py

@@ -44,6 +44,8 @@ class Wrapper:
 
     def __init__(self):
         self.loaded_dll = None
+        self.is_managed = Wrapper.__get_use_managed_mem()
+        self.force_cpu = Wrapper.__get_force_cpu()
 
         try:
             # Try from config if present
@@ -62,7 +64,9 @@ def __del__(self):
         self.__release_library()
 
     def __setup_library(self):
-        status = self.loaded_dll.cuBool_Initialize(ctypes.c_uint(bridge.get_init_hints(False, False)))
+        status = self.loaded_dll.cuBool_Initialize(ctypes.c_uint(bridge.get_init_hints(
+            force_cpu_backend=self.force_cpu, is_gpu_mem_managed=self.is_managed)))
+
         bridge.check(status)
 
     def __release_library(self):
@@ -76,3 +80,19 @@ def __get_lib_path(cls, prefix):
                 return prefix / entry
 
         return None
+
+    @classmethod
+    def __get_force_cpu(cls):
+        try:
+            memory = os.environ["CUBOOL_BACKEND"]
+            return True if memory.lower() == "cpu" else False
+        except KeyError:
+            return False
+
+    @classmethod
+    def __get_use_managed_mem(cls):
+        try:
+            memory = os.environ["CUBOOL_MEM"]
+            return True if memory.lower() == "managed" else False
+        except KeyError:
+            return False