Function PrintToPythonStdout

tensorflow/python/eager/pywrap_tfe_src.cc:3475–3495

A method prints incoming messages directly to Python's stdout using Python's C API. This is necessary in Jupyter notebooks and colabs where messages to the C stdout don't go to the notebook cell outputs, but calls to Python's stdout do.

// and colabs where messages to the C stdout don't go to the notebook
// cell outputs, but calls to Python's stdout do.
void PrintToPythonStdout(const char* msg) {
  if (Py_IsInitialized()) {
    PyGILState_STATE py_threadstate;
    py_threadstate = PyGILState_Ensure();

    string string_msg = msg;
    // PySys_WriteStdout truncates strings over 1000 bytes, so
    // we write the message in chunks small enough to not be truncated.
    int CHUNK_SIZE = 900;
    auto len = string_msg.length();
    for (size_t i = 0; i < len; i += CHUNK_SIZE) {
      PySys_WriteStdout("%s", string_msg.substr(i, CHUNK_SIZE).c_str());
    }

    // Force flushing to make sure print newlines aren't interleaved in
    // some colab environments
    PyRun_SimpleString("import sys; sys.stdout.flush()");

    PyGILState_Release(py_threadstate);
  }
}

// Register PrintToPythonStdout as a log listener, to allow
// printing in colabs and jupyter notebooks to work.