redirect stdcout to a stringstream so Python __str__() can properly return a string after calling the c++ print function

This is to avoid a printing issue in some Python's IDE when __str__() is called to update objects' values in Debug mode.

cython/gtsam/tests/gtsam_test.h

@@ -762,4 +762,11 @@ namespace utilities {
   gtsam::Values localToWorld(const gtsam::Values& local, const gtsam::Pose2& base, const gtsam::KeyVector& keys);
 
 } //\namespace utilities
+
+#include <gtsam/nonlinear/utilities.h>
+class RedirectCout {
+  RedirectCout();
+  string str();
+};
+
 } //\namespace gtsam

gtsam.h

@@ -2664,4 +2664,10 @@ namespace utilities {
 
 } //\namespace utilities
 
+#include <gtsam/nonlinear/utilities.h>
+class RedirectCout {
+  RedirectCout();
+  string str();
+};
+
 }

gtsam/nonlinear/utilities.h

@@ -250,6 +250,32 @@ Values localToWorld(const Values& local, const Pose2& base,
   return world;
 }
 
-}
+} // namespace utilities
+
+/**
+ * For Python __str__().
+ * Redirect std cout to a string stream so we can return a string representation
+ * of an object when it prints to cout.
+ * https://stackoverflow.com/questions/5419356/redirect-stdout-stderr-to-a-string
+ */
+struct RedirectCout {
+  /// constructor -- redirect stdout buffer to a stringstream buffer
+  RedirectCout() : ssBuffer_(), coutBuffer_(std::cout.rdbuf(ssBuffer_.rdbuf())) {}
+
+  /// return the string
+  std::string str() const {
+    return ssBuffer_.str();
+  }
+
+  /// destructor -- redirect stdout buffer to its original buffer
+  ~RedirectCout() {
+    std::cout.rdbuf(coutBuffer_);
+  }
+
+private:
+  std::stringstream ssBuffer_;
+  std::streambuf* coutBuffer_;
+};
+
 }
 

wrap/Method.cpp

@@ -100,9 +100,13 @@ void Method::emit_cython_pyx_no_overload(FileWriter& file,
                                          const Class& cls) const {
   string funcName = pyRename(name_);
   // leverage python's special treatment for print
-  if (funcName == "print_")
+  if (funcName == "print_") {
-    file.oss << "    def __str__(self):\n        self.print_('')\n        return ''\n";
+    //file.oss << "    def __str__(self):\n        self.print_('')\n        return ''\n";
-
+    file.oss << "    def __str__(self):\n";
+    file.oss << "      strBuf = RedirectCout()\n";
+    file.oss << "      self.print_('')\n";
+    file.oss << "      return strBuf.str()\n";
+  }
   // Function definition
   file.oss << "    def " << funcName;
   // modify name of function instantiation as python doesn't allow overloads