pyError.h

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//
// Copyright 2016 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_BASE_TF_PY_ERROR_H
#define PXR_BASE_TF_PY_ERROR_H

/// \file tf/error.h
/// Provide facilities for error handling in script.

#include "pxr/pxr.h"

#include "pxr/base/tf/api.h"
#include "pxr/base/tf/errorMark.h"

#include "pxr/external/boost/python/default_call_policies.hpp"

PXR_NAMESPACE_OPEN_SCOPE

/// Converts any \a TfError objects in \a m into python exceptions.  User code
/// should generally not have to call this.  User code should generally not
/// have to call this, unless it's manually bridging between C++ & Python.
TF_API
bool TfPyConvertTfErrorsToPythonException(TfErrorMark const &m);

/// Convert the current python exception to \a TfError objects and post them
/// to the error system.  User code should generally not have to call this,
/// unless it's manually bridging between C++ & Python.
TF_API
void TfPyConvertPythonExceptionToTfErrors();

/// \class TfPyRaiseOnError
///
/// A boost.python call policy class which, when applied to a wrapped
/// function, will create an error mark before calling the function, and check
/// that error mark after the function has completed.  If any TfErrors have
/// occurred, they will be raised as python exceptions.
///
/// This facility does not need to be used by clients in general.  It is only
/// required for wrapped functions and methods that do not appear directly in an
/// extension module.  For instance, the map and sequence proxy objects use
/// this, since they are created on the fly.
template <typename Base = pxr_boost::python::default_call_policies>
struct TfPyRaiseOnError : Base
{
  public:

    // This call policy provides a customized argument_package.  We need to do
    // this to store the TfErrorMark that we use to collect TfErrors that
    // occurred during the call and convert them to a python exception at the
    // end.  It doesn't work to do this in the precall() and postcall()
    // because if the call itself throws a c++ exception, the postcall() isn't
    // executed and we can't destroy the TfErrorMark, leaving it dangling.
    // Using the argument_package solves this since it is a local variable it
    // will be destroyed whether or not the call throws.  This is not really a
    // publicly documented boost.python feature, however.  :-/
    template <class BaseArgs>
    struct ErrorMarkAndArgs {
        /* implicit */ErrorMarkAndArgs(BaseArgs base_) : base(base_) {}
        operator const BaseArgs &() const { return base; }
        operator BaseArgs &() { return base; }
        BaseArgs base;
        TfErrorMark errorMark;
    };
    typedef ErrorMarkAndArgs<typename Base::argument_package> argument_package;

    /// Default constructor.
    TfPyRaiseOnError() {}

    // Only accept our argument_package type, since we must ensure that we're
    // using it so we track a TfErrorMark.
    bool precall(argument_package const &a) { return Base::precall(a); }

    // Only accept our argument_package type, since we must ensure that we're
    // using it so we track a TfErrorMark.
    PyObject *postcall(argument_package const &a, PyObject *result) {
        result = Base::postcall(a, result);
        if (result && TfPyConvertTfErrorsToPythonException(a.errorMark)) {
            Py_DECREF(result);
            result = NULL;
        }
        return result;
    }
};

PXR_NAMESPACE_CLOSE_SCOPE

#endif // PXR_BASE_TF_PY_ERROR_H