Fix Byte BPE string results for Python. (#512)

It ignores invalid UTF8 strings.

@@ -5,7 +5,9 @@
 #ifndef SHERPA_ONNX_CSRC_OFFLINE_RECOGNIZER_CTC_IMPL_H_
 #define SHERPA_ONNX_CSRC_OFFLINE_RECOGNIZER_CTC_IMPL_H_
 
+#include <ios>
 #include <memory>
+#include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
@@ -42,6 +44,15 @@ static OfflineRecognitionResult Convert(const OfflineCtcDecoderResult &src,
     }
     auto sym = sym_table[src.tokens[i]];
     text.append(sym);
+
+    if (sym.size() == 1 && sym[0] != ' ') {
+      // for byte bpe models
+      std::ostringstream os;
+      os << "<0x" << std::hex << std::uppercase
+         << (static_cast<int32_t>(sym[0]) & 0xff) << ">";
+      sym = os.str();
+    }
+
     r.tokens.push_back(std::move(sym));
   }
   r.text = std::move(text);

@@ -6,8 +6,10 @@
 #define SHERPA_ONNX_CSRC_OFFLINE_RECOGNIZER_TRANSDUCER_IMPL_H_
 
 #include <fstream>
+#include <ios>
 #include <memory>
 #include <regex>  // NOLINT
+#include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
@@ -44,6 +46,14 @@ static OfflineRecognitionResult Convert(
     auto sym = sym_table[i];
     text.append(sym);
 
+    if (sym.size() == 1 && sym[0] != ' ') {
+      // for byte bpe models
+      std::ostringstream os;
+      os << "<0x" << std::hex << std::uppercase
+         << (static_cast<int32_t>(sym[0]) & 0xff) << ">";
+      sym = os.str();
+    }
+
     r.tokens.push_back(std::move(sym));
   }
   r.text = std::move(text);

@@ -6,7 +6,9 @@
 #define SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_CTC_IMPL_H_
 
 #include <algorithm>
+#include <ios>
 #include <memory>
+#include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
@@ -35,6 +37,15 @@ static OnlineRecognizerResult Convert(const OnlineCtcDecoderResult &src,
     auto sym = sym_table[i];
 
     r.text.append(sym);
+
+    if (sym.size() == 1 && sym[0] != ' ') {
+      // for byte bpe models
+      std::ostringstream os;
+      os << "<0x" << std::hex << std::uppercase
+         << (static_cast<int32_t>(sym[0]) & 0xff) << ">";
+      sym = os.str();
+    }
+
     r.tokens.push_back(std::move(sym));
   }
 

@@ -6,8 +6,10 @@
 #define SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_TRANSDUCER_IMPL_H_
 
 #include <algorithm>
+#include <ios>
 #include <memory>
 #include <regex>  // NOLINT
+#include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
@@ -47,6 +49,15 @@ static OnlineRecognizerResult Convert(const OnlineTransducerDecoderResult &src,
     auto sym = sym_table[i];
 
     r.text.append(sym);
+
+    if (sym.size() == 1 && sym[0] != ' ') {
+      // for byte bpe models
+      std::ostringstream os;
+      os << "<0x" << std::hex << std::uppercase
+         << (static_cast<int32_t>(sym[0]) & 0xff) << ">";
+      sym = os.str();
+    }
+
     r.tokens.push_back(std::move(sym));
   }
 

@@ -23,8 +23,12 @@ Args:
 static void PybindOfflineRecognitionResult(py::module *m) {  // NOLINT
   using PyClass = OfflineRecognitionResult;
   py::class_<PyClass>(*m, "OfflineRecognitionResult")
-      .def_property_readonly("text",
-                             [](const PyClass &self) { return self.text; })
+      .def_property_readonly(
+          "text",
+          [](const PyClass &self) -> py::str {
+            return py::str(PyUnicode_DecodeUTF8(self.text.c_str(),
+                                                self.text.size(), "ignore"));
+          })
       .def_property_readonly("tokens",
                              [](const PyClass &self) { return self.tokens; })
       .def_property_readonly(

@@ -15,7 +15,11 @@ static void PybindOnlineRecognizerResult(py::module *m) {
   using PyClass = OnlineRecognizerResult;
   py::class_<PyClass>(*m, "OnlineRecognizerResult")
       .def_property_readonly(
-          "text", [](PyClass &self) -> std::string { return self.text; })
+          "text",
+          [](PyClass &self) -> py::str {
+            return py::str(PyUnicode_DecodeUTF8(self.text.c_str(),
+                                                self.text.size(), "ignore"));
+          })
       .def_property_readonly(
           "tokens",
           [](PyClass &self) -> std::vector<std::string> { return self.tokens; })