add lazy_attribute_loading_from_module builtin

- used to lazily load attributes defined in another module via the __getattr__ mechanism. This will only cache the attributes in the module where this is called.

Author: cosminbasca

graalpython/lib-graalpython/__graalpython__.py

@@ -39,18 +39,44 @@
 
 
 @builtin
-def import_current_as_named_module(module_name):
+def import_current_as_named_module(module_name, globals):
     """
     load a builtin anonymous module which does not have a Truffle land builtin module counter part
 
     :param module_name: the module name to load as
+    :param globals: the module globals (to update)
     :return: None
     """
     import sys
     module = sys.modules.get(module_name, None)
     if not module:
         module = type(sys)(module_name)
         sys.modules[module_name] = module
-    new_globals = dict(**globals())
+    new_globals = dict(**globals)
     new_globals.update(**module.__dict__)
     module.__dict__.update(**new_globals)
+
+
+@builtin
+def lazy_attribute_loading_from_module(attributes, module_name, globals):
+    """
+    used to lazily load attributes defined in another module via the __getattr__ mechanism.
+    This will only cache the attributes in the caller module.
+
+    :param attributes: a list of attributes names to be loaded lazily from the delagate module
+    :param module_name: the delegate module
+    :param globals: the module globals (to update)
+    :return:
+    """
+    def __getattr__(name):
+        if name in attributes:
+            delegate_module = __import__(module_name)
+            globals.update(delegate_module.__dict__)
+            globals['__all__'] = attributes
+            if '__getattr__' in globals:
+                del globals['__getattr__']
+            return getattr(delegate_module, name)
+        raise AttributeError("module '{}' does not have '{}' attribute".format(module_name, name))
+
+    globals['__getattr__'] = __getattr__
+    globals['__all__'] = ['__getattr__']

graalpython/lib-graalpython/_struct.py

@@ -37,57 +37,8 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-# __all__ = ['Struct', '_clearcache', 'calcsize', 'error', 'iter_unpack', 'pack', 'pack_into', 'unpack', 'unpack_from']
 
-
-@__graalpython__.builtin
-def _clearcache(*args):
-    import _cpython_struct
-    return _cpython_struct.clearcache(*args)
-
-
-@__graalpython__.builtin
-def calcsize(fmt):
-    import _cpython_struct
-    return _cpython_struct.calcsize(fmt)
-
-
-@__graalpython__.builtin
-def iter_unpack(fmt, buffer):
-    import _cpython_struct
-    return _cpython_struct.calcsize(fmt, buffer)
-
-
-@__graalpython__.builtin
-def pack(fmt, *vals):
-    import _cpython_struct
-    return _cpython_struct.pack(fmt, *vals)
-
-
-@__graalpython__.builtin
-def pack_into(fmt, buffer, offset, *vals):
-    import _cpython_struct
-    return _cpython_struct.pack_into(fmt, buffer, offset, *vals)
-
-
-@__graalpython__.builtin
-def unpack(fmt, *vals):
-    import _cpython_struct
-    return _cpython_struct.unpack(fmt, *vals)
-
-
-@__graalpython__.builtin
-def unpack_from(fmt, buffer, offset=0):
-    import _cpython_struct
-    return _cpython_struct.unpack_from(fmt, buffer, offset=offset)
-
-
-# error and Struct
-def __getattr__(name):
-    if name in ['error', 'Struct']:
-        import _cpython_struct
-        return __getattr__(_cpython_struct, name)
-    raise AttributeError("module {} has no attribute {}".format(__name__, name))
-
-
-__graalpython__.import_current_as_named_module("_struct")
+__graalpython__.lazy_attribute_loading_from_module(
+    ['Struct', '_clearcache', 'calcsize', 'error', 'iter_unpack', 'pack', 'pack_into', 'unpack', 'unpack_from'],
+    '_cpython_struct', globals())
+__graalpython__.import_current_as_named_module("_struct", globals())