PySequenceHolder.h

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//
// Copyright (c) 2003-2006 greg Landrum and Rational Discovery LLC
//
//   @@ All Rights Reserved @@
//  This file is part of the RDKit.
//  The contents are covered by the terms of the BSD license
//  which is included in the file license.txt, found at the root
//  of the RDKit source tree.
//
 
#include <RDGeneral/export.h>
#ifndef _RD_PYSEQUENCEHOLDER_H_
#define _RD_PYSEQUENCEHOLDER_H_
 
//
// Defines a class to hold sequences passed in from Python
//
#include "Wrap.h"
#include <RDGeneral/Invariant.h>
 
namespace python = boost::python;
 
//! \brief Class to hold sequences (lists, tuples, arrays, etc.)
//!         passed from Python -> C++
//!
//!  PySequenceHolder is templated on the type of the contained object.
//!
//!  The class is \em lazy: elements are not evaluated until requested
//!     within the C++ code.
//!
template <typename T>
class PySequenceHolder {
 public:
  PySequenceHolder(python::object seq) { d_seq = seq; }
 
  // --------------------------------------------------
  //! \brief Returns the size of the contained sequence.
  //!
  //! NOTE: the sequence must have a \c __len__ attribute, otherwise
  //!       a \c ValueError will be raised.
  unsigned int size() const {
    unsigned int res = 0;
    try {
      res = python::extract<int>(d_seq.attr("__len__")());
    } catch (...) {
      throw_value_error("sequence does not support length query");
    }
    return res;
  }
 
  // --------------------------------------------------
  //! \brief Returns an element of the sequence
  //!
  //! ARGUMENTS:
  //!   - which: an integer specifying which element should be returned.
  //!
  //! NOTES:
  //!   - if the sequence is not \a which elements long, we raise an
  //!     \c IndexError
  //!   - if the element cannot be converted to type \c T, we raise a
  //!     \c ValueError
  T operator[](unsigned int which) const {
    if (which > size()) {
      throw_index_error(which);
    }
 
    try {
      T res = python::extract<T>(d_seq[which]);
      return res;
    } catch (...) {
      throw_value_error("cannot extract desired type from sequence");
    }
 
    POSTCONDITION(0, "cannot reach this point");
    return static_cast<T>(T());
  }
 
 private:
  python::object d_seq;
};
 
#endif