Strange behavior with ternary operator #493

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1. stefanseefeld commented on Jun 20, 2025

   

   stefanseefeld

   on Jun 20, 2025

   Last edited by stefanseefeld

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   I wouldn't be surprised if this behaviour is the result of expression templates at work.
   Try using a temporary variable to prevent lazy evaluation of the expression on the right-hand side.
   Also, to confirm: what is the result of calling the function you got ? That is, what is the output of
   py::exec("print(type(mol()))", globals); ?
2. sadseeker commented on Jun 20, 2025

   

   sadseeker

   on Jun 20, 2025

   Last edited by sadseeker

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   Thanks for answer.
   I can fix this by using simple if-else or casting dict and list to py::object explicitly.
   But I wonder if this is expected behavior or bug

   ---

   py::exec("print(type(mol()))", globals); ?

   Probably <class 'list'> because I saw in debugger that &object::ptr would be written to globals["mol"].
   Although I can't test right now

   ---

   PS:

   py::exec("print(type(mol()))", globals); ?

   output:

   PythonException:
   Type: ArgumentError
   Value: Python argument types in
   None.None()
   did not match C++ signature:
   None(class boost::python::api::object {lvalue})
   Traceback:
    <string> : 1
   
3. e-kwsm commented on Oct 24, 2025

   

   e-kwsm

   on Oct 24, 2025

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   globals["mol"] = condition ? dict : list;

   Here dict and list must have the same type.

   Try the folowing code

     globals["foo"] = true ? false : 123;  // false is converted to (int)0
     globals["bar"] = false;
     boost::python::exec("print(foo, bar)", globals);

   which prints

   0 False
   

   See https://stackoverflow.com/a/8535301.

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