Use relative import during build from source

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Author: larryliu0820

codegen/parse.py

@@ -4,8 +4,12 @@
 from typing import Any
 
 import yaml
-
-from executorch.codegen.model import ETKernelIndex, ETKernelKey
+try:
+    from executorch.codegen.model import ETKernelIndex, ETKernelKey
+except ImportError:
+    # If we build from source, executorch.codegen is not available.
+    # We can use relative import instead.
+    from .model import ETKernelIndex, ETKernelKey
 from torchgen.gen import LineLoader, parse_native_yaml
 from torchgen.model import (
     BackendMetadata,

codegen/tools/gen_oplist.py

@@ -12,7 +12,12 @@
 from typing import Any, Dict, List, Optional, Set
 
 import yaml
-from executorch.codegen.parse import strip_et_fields
+try:
+    from executorch.codegen.parse import strip_et_fields
+except ImportError:
+    # If we build from source, executorch.codegen is not available.
+    # We can use relative import instead.
+    from ..parse import strip_et_fields
 
 from torchgen.gen import LineLoader, parse_native_yaml_struct
 from torchgen.selective_build.operator import SelectiveBuildOperator