I am writing a C++ application (based on Tensorflow Serving) in which I need to call Python and Numpy functions (from Python.h and numpy.h).
This application is built with Bazel.
So I include the header:
#include "tensorflow/python/lib/core/numpy.h"
which in turn includes Python.h.
This file seems to wrap numpy to fix an issue described in this Stack Overflow post.
Any other C++ code within the Tensorflow project which needs to make calls to Python.h also does not directly include it, but only includes tensorflow/python/lib/core/numpy.h. On the Bazel side, it seems to suffice to simply add //util/python:python_headers to the deps of the build.
My BUILD file looks like this:
...
cc_library(
name = "my_library",
srcs = ["my_library.cc"],
hdrs = ["my_library.h"],
deps = [
@org_tensorflow//util/python:python_headers",
@org_tensorflow//third_party/py/numpy:headers",
] + SOME_OTHER_DEPS + TENSORFLOW_DEPS + SUPPORTED_TENSORFLOW_OPS,
)
cc_binary(
name = "my_main",
srcs = ["my_main.cc"],
deps = [":my_library"],
)
...
Building the library with bazel build :my_library works fine.
Building the binary the same way does not work, I get the following errors:
bazel-out/local-fastbuild/bin/servable/_objs/my_library/servable/my:library.pic.o:my_library.cc:function tensorflow::serving::NumpyInitializer::init(): error: undefined reference to 'Py_Initialize'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::MakeArgTuple(tensorflow::(anonymous namespace)::PyCall*, _object**): error: undefined reference to 'PyList_New'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::MakeArgTuple(tensorflow::(anonymous namespace)::PyCall*, _object**): error: undefined reference to 'PyList_SetItem'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::MakeArgTuple(tensorflow::(anonymous namespace)::PyCall*, _object**): error: undefined reference to 'Py_BuildValue'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::IsSingleNone(_object*): error: undefined reference to 'PyType_IsSubtype'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::IsSingleNone(_object*): error: undefined reference to '_Py_NoneStruct'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::DoCallPyFunc(tensorflow::(anonymous namespace)::PyCall*): error: undefined reference to 'PyEval_CallObjectWithKeywords'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::DoCallPyFunc(tensorflow::(anonymous namespace)::PyCall*): error: undefined reference to 'PyErr_Occurred'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::DoCallPyFunc(tensorflow::(anonymous namespace)::PyCall*): error: undefined reference to 'PyErr_Print'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::DoCallPyFunc(tensorflow::(anonymous namespace)::PyCall*): error: undefined reference to 'PyList_Size'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::DoCallPyFunc(tensorflow::(anonymous namespace)::PyCall*): error: undefined reference to 'PyList_GetItem'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::(anonymous namespace)::DoCallPyFunc(tensorflow::(anonymous namespace)::PyCall*): error: undefined reference to 'PyType_IsSubtype'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::ConvertNdarrayToTensor(_object*, tensorflow::Tensor*): error: undefined reference to 'PyString_AsStringAndSize'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::ConvertTensorToNdarray(tensorflow::Tensor const&, _object**): error: undefined reference to 'PyString_FromStringAndSize'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::PyFuncOp::Compute(tensorflow::OpKernelContext*): error: undefined reference to 'PyGILState_Ensure'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/py_func_lib/external/org_tensorflow/tensorflow/python/lib/core/py_func.pic.o:py_func.cc:function tensorflow::PyFuncOp::Compute(tensorflow::OpKernelContext*): error: undefined reference to 'PyGILState_Release'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/numpy_lib/external/org_tensorflow/tensorflow/python/lib/core/numpy.pic.o:numpy.cc:function _import_array: error: undefined reference to 'PyImport_ImportModule'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/numpy_lib/external/org_tensorflow/tensorflow/python/lib/core/numpy.pic.o:numpy.cc:function _import_array: error: undefined reference to 'PyExc_ImportError'
bazel-out/local-fastbuild/bin/external/org_tensorflow/tensorflow/python/_objs/numpy_lib/external/org_tensorflow/tensorflow/python/lib/core/numpy.pic.o:numpy.cc:function _import_array: error: undefined reference to 'PyErr_SetString'
So there is obviously linking errors against Python.h. However, compiling any Tensorflow-internal goals works fine. I find it weird that it now can not link to Python.h even inside Tensorflow files.
After spending a few days looking into Tensorflow and their BUILD files I am out of ideas how to make this work.
Some clues seem to be in the definitions in util/python/BUILD and tensorflow/tensorflow.bzl.
There seems to be quite a bit of Bazel magic going on there.
You need to link your executable against libpython.(a|so). Your compile actions correctly made use of python.h and put some undefined symbols into objects. When building executable, linking action needs to resolve all undefined symbols, so it's no longer enough to have python.h, you need "python.cc".
My knowledge of tensorflow is rather poor, maybe somebody from the team can comment further if your use case is a solved problem. For general Bazel solution to "How to provide libpython" I'd recommend external repositories and their rules. I think this email thread will get you almost to the end.
Or you can copy the library over into your workspace and put it as a src to cc_binary rule.