# Chapter 2. Configuration

### David Abrahams

Copyright © 2002-2015 David Abrahams, Stefan Seefeld

### Configuration

#### Introduction

Boost.Python uses several configuration macros in `<boost/config.hpp>`, as well as configuration macros meant to be supplied by the application. These macros are documented here.

#### Application Defined Macros

These are the macros that may be defined by an application using Boost.Python. Note that if you extend a strict interpretation of the C++ standard to cover dynamic libraries, using different values of these macros when compiling different libraries (including extension modules and the Boost.Python library itself) is a violation of the ODR. However, we know of no C++ implementations on which this particular violation is detectable or causes any problems.

Macro | Default | Meaning
--- | --- | ---
BOOST_PYTHON_MAX_ARITY | 15 | The maximum arity of any function, member function, or constructor to be wrapped, invocation of a Boost.Python function wich is specified as taking arguments x1, x2,...Xn. This includes, in particular, callback mechanisms such as object::operator()(...) or call_method<R>(... ).
BOOST_PYTHON_MAX_BASES | 10 | The maximum number of template arguments to the `bases<...>` class template, which is used to specify the bases of a wrapped C++ class..
BOOST_PYTHON_STATIC_MODULE | not defined | If defined, prevents your module initialization function from being treated as an exported symbol on platforms which support that distinction in-code
BOOST_PYTHON_ENABLE_CDECL | not defined | If defined, allows functions using the `__cdecl` calling convention to be wrapped.
BOOST_PYTHON_ENABLE_STDCALL | not defined | If defined, allows functions using the `__stdcall` calling convention to be wrapped.
BOOST_PYTHON_ENABLE_FASTCALL | not defined | If defined, allows functions using the `__fastcall` calling convention to be wrapped.

#### Library Defined Defined Macros

These macros are defined by Boost.Python and are implementation details of interest only to implementors and those porting to new platforms.

Macro | Default | Meaning
--- | --- | ---
BOOST_PYTHON_TYPE_ID_NAME | not defined | If defined, this indicates that the type_info comparison across shared library boundaries does not work on this platform. In other words, if shared-lib-1 passes `typeid(T)` to a function in shared-lib-2 which compares it to `typeid(T)`, that comparison may return `false`. If this macro is #defined, Boost.Python uses and compares `typeid(T).name()` instead of using and comparing the `std::type_info` objects directly.
BOOST_PYTHON_NO_PY_SIGNATURES | not defined | If defined for a module no pythonic signatures are generated for the docstrings of the module functions, and no python type is associated with any of the converters registered by the module. This also reduces the binary size of the module by about 14% (gcc compiled). If defined for the boost_python runtime library, the default for the `docstring_options.enable_py_signatures()` is set to `false`.
BOOST_PYTHON_SUPPORTS_PY_SIGNATURES | defined if `BOOST_PYTHON_NO_PY_SIGNATURES` is undefined | This macro is defined to enable a smooth transition from older Boost.Python versions which do not support pythonic signatures. For example usage see here.
BOOST_PYTHON_PY_SIGNATURES_PROPER_INIT_SELF_TYPE | not defined | If defined the python type of `__init__` method "self" parameters is properly generated, otherwise object is used. It is undefined by default because it increases the binary size of the module by about 14% (gcc compiled).