marshal.rst

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 ~.Message.pb class method.