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feat: added ParseFromString method to message for compatibility #336

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feat: added ParseFromString method to message for compatibility #336

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23 changes: 23 additions & 0 deletions src/betterproto/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1022,6 +1022,29 @@ def FromString(cls: Type[T], data: bytes) -> T:
"""
return cls().parse(data)

# For compatibility with Google protobuf official implementation.
def ParseFromString(self, data: bytes) -> T:
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Suggested change
def ParseFromString(self, data: bytes) -> T:
def ParseFromString(self: T, data: bytes) -> T:

"""
Parse the binary encoded Protobuf into this message instance. This
returns the instance itself and is therefore assignable and chainable.

.. note::
This is a method for compatibility with other libraries,
you should really use :meth:`parse`.


Parameters
-----------
data: :class:`bytes`
The data to parse the protobuf from.

Returns
--------
:class:`Message`
The initialized message.
"""
return self.parse(data)
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Isn't this slightly different from the offical implementation which clears any currently set values? https://github.com/protocolbuffers/protobuf/blob/2a2a9b6e64e0cda49b0e5377cad58c790087e1c9/python/google/protobuf/message.py#L193-L199

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This indeed seems to be the case.

I've added a simple example which shows the difference in result from ParseFromString with the one from this PR:

syntax = "proto3";

package some.package.name;

message Cat {
  int64 age = 1;
  int64 lives = 2;
}
def ParseFromString(self, data: bytes):
    return self.parse(data)

if __name__ == '__main__':
    # Create bytes
    cat = Cat(
        age=5,
        # lives=9,
    )

    data = cat.SerializeToString()

    # Dynamically add ParseFromString to the Cat class
    Cat.ParseFromString = ParseFromString

    # ParseFromString for the betterproto cat and the pb2 cat
    cat_betterproto = Cat(age=3, lives=8)
    cat_pb2 = Cat_pb2(age=3, lives=8)

    cat_betterproto.ParseFromString(data)
    cat_pb2.ParseFromString(data)

    print(cat_betterproto)  # Cat(age=5, lives=8), lives are not cleared
    print(cat_pb2)  # age: 5, lives are cleared
    assert cat_pb2.lives == 0


def to_dict(
self, casing: Casing = Casing.CAMEL, include_default_values: bool = False
) -> Dict[str, Any]:
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9 changes: 9 additions & 0 deletions tests/test_features.py
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Expand Up @@ -485,3 +485,12 @@ def test_service_argument__expected_parameter():
do_thing_request_parameter = sig.parameters["do_thing_request"]
assert do_thing_request_parameter.default is Parameter.empty
assert do_thing_request_parameter.annotation == "DoThingRequest"


def test_message_parse_from_string():
@dataclass
class SimpleMessage(betterproto.Message):
message: str = betterproto.string_field(1)

test_message = SimpleMessage(message="test message")
assert test_message == SimpleMessage().ParseFromString(bytes(test_message))