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boost-python

How to accept both string or None argument to Boost Python function

It is Pythonic to use None as the default for an optional argument. For example, use None as the default of a string argument:

def f(str_arg=None):
    if str_arg is None:
        str_arg = get_str_arg_default()
    ...

Thus f() accepts two types for argument str_arg: a string or None.

Now, we are implementing this function in C++ using Boost Python. How do I make Boost Python accept both string and None types for an argument?

Solution

  • Can you have the function accept a boost::python::object? Then you can check if it is None by calling is_none().

    See https://wiki.python.org/moin/boost.python/FAQ#How_can_I_check_returning_Python_value_for_None.3F which gives several suggestions for checking if an object is None - e.g. arg.ptr() == object().ptr(), arg.ptr() == Py_None or arg.is_none().