Interaction between C++ and Python¶
Users employ API in Python to describe their own network, however, the network construction actually happens in C++. so Protobuf is introduced to send the message between Python and C++.
The Interaction between Python and C++ can be simplified as two steps:
- C++ tells Python how many Ops there are, and what parameter do users need to offer to initialize a new Op. Python then builds API for each Op at compile time.
- Users invoke APIs built by Python and provide necessary parameters. These parameters will be sent to C++ for finishing the Op construction task.
Message from C++ to Python¶
We define a Protobuf message class OpProto to hold message needed in the first step. What should an OpProto contain? This question is equivalent to “What message do we need to offer, to build a Python API which is legal and user oriented and can use to describe a whole Op.”
Following message are necessary:
- Op’s name, and its simple comment.
- Input and output variable number; each variable’s name, type, and comment.
- Op’s attributes; each attribute includes name, type, comment, default value and value range.
So OpProto can be defined as follows:
enum AttrType {
INT = 1;
FLOAT = 2;
STRING = 3;
INTS = 4;
FLOATS = 5;
STRINGS = 6;
};
message AttrValue {
AttrType type = 1;
optional int iv = 2;
optional float fv = 3;
optional string sv = 4;
repeated int ivs = 5;
repeated float fvs = 6;
repeated string svs = 7;
};
message AttrProto {
required string name = 1;
required string comment = 2;
required AttrType type = 3;
};
message VarProto {
required string name = 1;
required string comment = 2;
required bool is_tensor = 3;
};
message OpProto {
repeated VarProto inputs = 1;
repeated VarProto outputs = 2;
repeated AttrProto attrs = 3;
required string type = 4;
required string comment = 5;
};
To generate Python code automatically:
def create_python_ops_creatation_functions():
op_protos = paddle.framework.OpRegistry.get_all_op_proto()
for type_name in op_protos:
op_proto = op_protos[type_name]
def __impl__(**kwargs): # User must use key word args in Paddle API
inputs = [kwargs.get(ipt.name, "") for ipt in op_proto.inputs]
outputs = [kwargs.get(opt.name, "") for opt in op_proto.outputs]
attrs = [cast_to_op_attr(attr, kwargs.get(attr.name, None)) for attr in op_proto.attrs]
opdesc = （input, outputs, type_name, attrs）
return paddle.framework.OpRegistry.CreateOp(opdesc)
__impl__.__doc__ = create_doc_string(op_proto)
globals()[type_name] = __impl__
create_python_ops_creatation_functions()
Message from Python to C++¶
To hold message needed in the above second step, we define Protobuf message class OpDesc. It is used to hold user-specified parameters in Op describing.
message OpDesc {
required string type = 1;
repeated string inputs = 2;
repeated string outputs = 3;
map<string, AttrValue> attrs = 4;
};
OpProto Register¶
Every Op has its own OpProto. For using convenience, we need to register them and record all their messages. For each Op class, we define a corresponding OpMaker class, in whose constructor we implement the OpProto‘s building process. OpMaker‘s constructor will be invoked by another function OpRegistry::RegisterOp().
class OpProtoMaker {
public:
OpProtoMaker(OpProto* proto): proto_(proto) {}
protected:
OpProto* proto_;
void AddInput(const std::string& name, const std::string& desc) {...}
void AddAttr(const std::string& name, const std::string& desc, TypeId type) {...}
void AddComment(const std::string& comment) { ... }
};
class OpRegistry {
public:
using OpCreator = std::function<OperatorBase* (OpDesc& desc)>;
template <typename OpType, typename OpMaker>
static void RegisterOp(const std::string& name) {
gCreators_[name] = [](const OpDesc& desc) {
return new OpType(desc);
};
OpProto& opProto = gProtos_[name];
OpMaker()(&opProto);
}
static map<string, OpCreator> gCreators_;
static map<string, OpProto> gProtos_;
};
template <typename OpType, typename OpMaker>
class OpRegister {
public:
OpRegister(std::string type) {
OpRegistry::RegisterOp<OpType, OpMaker>(type);
}
};
#define REGISTER_OP(op_class, op_maker_class, type_name) \
class op_class##Register { \
private: \
const static OpRegister<#op_class, #op_maker_class> reg; \
}; \
const Register op_class##Register::reg(#type_name);
class CosineOp {
// ...
}
struct CosineOpProtoMaker : public OpProtoMaker {
CosineOpProtoMaker(OpProto* proto) : OpProtoMaker(proto) {
AddInput("input", "input of cosine op");
AddAttr("scale", "scale of cosine op", float).Default(1.0).GreaterThan(0.0);
AddType("cos");
AddComment("This is cos op");
}
}
REGISTER_OP(CosineOp, CosineOpProtoMaker, cos);
In REGISTER_OP(CosineOp, CosineOpProtoMaker, cos), we register not only CosineOp but also CosineOpProto. As fields of CosineOpProto, the default value and value range of scale are also registered here.
Python API¶
Python APIs are divided into two types, high-level API and low-level API.
High-Level API¶
High-level API is called by users directly, so it should keep its style consistent with existing V2 APIs.
Here is a sample about how a define a fc layer:
hd = fc_layer(input=data, size=56, with_bias=True, activation="sigmoid");
hd is the output of fc_layer and it’s a variable. It can be further sent into other layers as input.
The definition of fc_layer():
def fc_layer(input, size, with_bias, activation):
attr_map = {"size":size}
check_attrs(attr_map)
w = make_variable('w')
if with_bias:
b = make_variable('b')
else:
b = None
fc_output = make_variable('fc_output');
fc_op(input, w, b, fc_output, attr_map)
act_output = make_variable('sigmod_output');
if activation == "sigmod":
sigmod_op(fc_output, act_output);
elif:
# ...
return act_output;
Low Leval API¶
In above sample, fc_op and sigmod_op are low-level API. They build OpDesc and invoke corresponding C++ code.
TODO