# Type Marshaling

Proto Plus provides a service that converts between protocol buffer objects and native Python types (or the wrapper types provided by this library).

This allows native Python objects to be used in place of protocol buffer messages where appropriate. In all cases, we return the native type, and are liberal on what we accept.

## Well-known types

The following types are currently handled by Proto Plus:

Protocol buffer type | Python type | Nullable
--- | --- | ---
`google.protobuf.BoolValue` | `bool` | Yes
`google.protobuf.BytesValue` | `bytes` | Yes
`google.protobuf.DoubleValue` | `float` | Yes
`google.protobuf.Duration` | `datetime.timedelta` | –
`google.protobuf.FloatValue` | `float` | Yes
`google.protobuf.Int32Value` | `int` | Yes
`google.protobuf.Int64Value` | `int` | Yes
`google.protobuf.ListValue` | `MutableSequence` | Yes
`google.protobuf.StringValue` | `str` | Yes
`google.protobuf.Struct` | `MutableMapping` | Yes
`google.protobuf.Timestamp` | `datetime.datetime` | Yes
`google.protobuf.UInt32Value` | `int` | Yes
`google.protobuf.UInt64Value` | `int` | Yes
`google.protobuf.Value` | JSON-encodable values | Yes

Note

Protocol buffers include well-known types for `Timestamp` and `Duration`, both of which have nanosecond precision. However, the Python `datetime` and `timedelta` objects have only microsecond precision. This library converts timestamps to an implementation of `datetime.datetime`, DatetimeWithNanoseconds, that includes nanosecond precision.

If you write a timestamp field using a Python `datetime` value, any existing nanosecond precision will be overwritten.

Note

Setting a `bytes` field from a string value will first base64 decode the string. This is necessary to preserve the original protobuf semantics when converting between Python dicts and proto messages. Converting a message containing a bytes field to a dict will base64 encode the bytes field and yield a value of type str.

    import proto
    from google.protobuf.json_format import ParseDict

    class MyMessage(proto.Message):
        data = proto.Field(proto.BYTES, number=1)

    msg = MyMessage(data=b"this is a message")
    msg_dict = MyMessage.to_dict(msg)

    # Note: the value is the base64 encoded string of the bytes field.
    # It has a type of str, NOT bytes.
    assert type(msg_dict['data']) == str

    msg_pb = ParseDict(msg_dict, MyMessage.pb())
    msg_two = MyMessage(msg_dict)

    assert msg == msg_pb == msg_two

## Wrapper types

Additionally, every `Message` subclass is a wrapper class. The creation of the class also creates the underlying protocol buffer class, and this is registered to the marshal.

The underlying protocol buffer message class is accessible with the `pb()` class method.