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boost/python/operators.hpp

Introduction
Class self_ns::self_t
Class template other
Class template detail::operator_
Object self
Example

<boost/python/operators.hpp> provides types and functions for automatically generating Python special methods from the corresponding C++ constructs. Most of these constructs are operator expressions, hence the name. To use the facility, substitute the self object for an object of the class type being wrapped in the expression to be exposed, and pass the result to class_<>::def(). Much of what is exposed in this header should be considered part of the implementation, so is not documented in detail here.

self_ns::self_t is the actual type of the self object. The library isolates self_t in its own namespace, self_ns, in order to prevent the generalized operator templates which operate on it from being found by argument-dependent lookup in other contexts. This should be considered an implementation detail, since users should never have to mention self_t directly.

namespace boost { namespace python { namespace self_ns {
{
   unspecified-type-declaration self_t;

   // inplace operators
   template <class T> operator_<unspecified> operator+=(self_t, T);
   template <class T> operator_<unspecified> operator-=(self_t, T);
   template <class T> operator_<unspecified> operator*=(self_t, T);
   template <class T> operator_<unspecified> operator/=(self_t, T);
   template <class T> operator_<unspecified> operator%=(self_t, T);
   template <class T> operator_<unspecified> operator>>=(self_t, T);
   template <class T> operator_<unspecified> operator<<=(self_t, T);
   template <class T> operator_<unspecified> operator&=(self_t, T);
   template <class T> operator_<unspecified> operator^=(self_t, T);
   template <class T> operator_<unspecified> operator|=(self_t, T);

   // comparisons
   template <class L, class R> operator_<unspecified> operator==(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator!=(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator<(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator>(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator<=(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator>=(L const&, R const&);

   // non-member operations
   template <class L, class R> operator_<unspecified> operator+(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator-(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator*(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator/(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator%(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator>>(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator<<(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator&(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator^(L const&, R const&);
   template <class L, class R> operator_<unspecified> operator|(L const&, R const&);
   template <class L, class R> operator_<unspecified> pow(L const&, R const&);

   // unary operations
   operator_<unspecified> operator-(self_t);
   operator_<unspecified> operator+(self_t);
   operator_<unspecified> operator~(self_t);
   operator_<unspecified> operator!(self_t);

   // value operations
   operator_<unspecified> int_(self_t);
   operator_<unspecified> long_(self_t);
   operator_<unspecified> float_(self_t);
   operator_<unspecified> complex_(self_t);
   operator_<unspecified> str(self_t);

   operator_<unspecified> repr(self_t);
}}};

The tables below describe the methods generated when the results of the expressions described are passed as arguments to class_<>::def(). x is an object of the class type being wrapped.

In the table below, If r is an object of type other<T>, y is an object of type T; otherwise, y is an object of the same type as r.

C++ Expression

Python Method Name

C++ Implementation

self += r

__iadd__

x += y

self -= r

__isub__

x -= y

self *= r

__imul__

x *= y

self /= r

__idiv__

x /= y

self %= r

__imod__

x %= y

self >>= r

__irshift__

x >>= y

self <<= r

__ilshift__

x <<= y

self &= r

__iand__

x &= y

self ^= r

__ixor__

x ^= y

self |= r

__ior__

x |= y

In the tables below, if r is of type self_t, y is an object of the same type as x; if l or r is an object of type other<T>, y is an object of type T; otherwise, y is an object of the same type as l or r. l is never of type self_t.

The column of Python Expressions illustrates the expressions that will be supported in Python for objects convertible to the types of x and y. The secondary operation arises due to Python's reflection rules for rich comparison operators, and are only used when the corresponding operation is not defined as a method of the y object.

C++ Expression

Python Method Name

C++ Implementation

Python Expression (primary, secondary)

self == r

__eq__

x == y

x == y, y == x

l == self

__eq__

y == x

y == x, x == y

self != r

__ne__

x != y

x != y, y != x

l != self

__ne__

y != x

y != x, x != y

self < r

__lt__

x < y

x < y, y > x

l < self

__gt__

y < x

y > x, x < y

self > r

__gt__

x > y

x > y, y < x

l > self

__lt__

y > x

y < x, x > y

self <= r

__le__

x <= y

x <= y, y >= x

l <= self

__ge__

y <= x

y >= x, x <= y

self >= r

__ge__

x >= y

x >= y, y <= x

l <= self

__le__

y >= x

y <= x, x >= y

The operations whose names begin with "__r" below will only be called if the left-hand operand does not already support the given operation, as described here.

C++ Expression

Python Method Name

C++ Implementation

self + r

__add__

x + y

l + self

__radd__

y + x

self - r

__sub__

x - y

l - self

__rsub__

y - x

self * r

__mult__

x * y

l * self

__rmult__

y * x

self / r

__div__

x / y

l / self

__rdiv__

y / x

self % r

__mod__

x % y

l % self

__rmod__

y % x

self >> r

__rshift__

x >> y

l >> self

__rrshift__

y >> x

self << r

__lshift__

x << y

l << self

__rlshift__

y << x

self & r

__and__

x & y

l & self

__rand__

y & x

self ^ r

__xor__

x ^ y

l ^ self

__rxor__

y ^ x

self | r

__or__

x | y

l | self

__ror__

y | x

pow(self, r)

__pow__

x ** y

pow(l, self)

__rpow__

y ** x

C++ Expression

Python Method Name

C++ Implementation

-self

__neg__

-x

+self

__pos__

+x

~self

__invert__

~x

not self or !self

__nonzero__

!!x

C++ Expression

Python Method Name

C++ Implementation

int_(self)

__int__

long(x)

long_(self)

__long__

PyLong_FromLong(x)

float_(self)

__float__

double(x)

complex_(self)

__complex__

std::complex<double>(x)

str(self)

__str__

lexical_cast<std::string>(x)

repr(self)

__repr__

lexical_cast<std::string>(x)

Instances of other<T> can be used in operator expressions with self; the result is equivalent to the same expression with a T object in place of other<T>. Use other<T> to prevent construction of a T object in case it is heavyweight, when no constructor is available, or simply for clarity.

namespace boost { namespace python
{
  template <class T>
  struct other
  {
  };
}}

Instantiations of detail::operator_<> are used as the return type of operator expressions involving self. This should be considered an implementation detail and is only documented here as a way of showing how the result of self-expressions match calls to class_<>::def().

namespace boost { namespace python { namespace detail
{
  template <unspecified>
  struct operator_
  {
  };
}}}
namespace boost { namespace python
{
  using self_ns::self;
}}
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/operators.hpp>
#include <boost/operators.hpp>

struct number
   : boost::integer_arithmetic<number>
{
    explicit number(long x_) : x(x_) {}
    operator long() const { return x; }

    template <class T>
    number& operator+=(T const& rhs)
    { x += rhs; return *this; }

    template <class T>
    number& operator-=(T const& rhs)
    { x -= rhs; return *this; }

    template <class T>
    number& operator*=(T const& rhs)
    { x *= rhs; return *this; }

    template <class T>
    number& operator/=(T const& rhs)
    { x /= rhs; return *this; }

    template <class T>
    number& operator%=(T const& rhs)
    { x %= rhs; return *this; }

   long x;
};

using namespace boost::python;
BOOST_PYTHON_MODULE(demo)
{
   class_<number>("number", init<long>())
      // interoperate with self
      .def(self += self)
      .def(self + self)
      .def(self -= self)
      .def(self - self)
      .def(self *= self)
      .def(self * self)
      .def(self /= self)
      .def(self / self)
      .def(self %= self)
      .def(self % self)

      // Convert to Python int
      .def(int_(self))

      // interoperate with long
      .def(self += long())
      .def(self + long())
      .def(long() + self)
      .def(self -= long())
      .def(self - long())
      .def(long() - self)
      .def(self *= long())
      .def(self * long())
      .def(long() * self)
      .def(self /= long())
      .def(self / long())
      .def(long() / self)
      .def(self %= long())
      .def(self % long())
      .def(long() % self)
      ;
}

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