4.1.1 Modes

There are five different conversion modes, identified by the following constants (provided by the rpy module) and another constant to indicate the absence of a global mode:

• PROC_CONVERSION
• CLASS_CONVERSION
• BASIC_CONVERSION
• VECTOR_CONVERSION
• NO_CONVERSION
• NO_DEFAULT

The rpy module provides three functions for manipulating the conversion modes:

get_default_mode()

Get the default conversion mode. It returns some of the previous constants (actually, an integer from the set {-1,0,1,2}, but you should use the literal constant rather than the numeric value).

set_default_mode(m)

Set the default conversion mode to m.

with_mode(m, fun)

Wrap the function fun in the conversion mode m. It returns a new function which accepts the same parameters as fun but, when called, it is evaluated in the conversion mode m. For example:

>>> set_default_mode(BASIC_CONVERSION)
>>> r.seq(1,3)
[1, 2, 3]
>>> with_mode(NO_CONVERSION, r.seq)(1,3)
<Robj object at 0x8acb2a0>

The result of a call to a Robj object is converted according to the following rules:

1. If the default mode has a value in the set {PROC_CONVERSION, CLASS_CONVERSION, BASIC_CONVERSION, NO_CONVERSION}, that mode is used.
2. If the default mode has the value NO_DEFAULT, then the object’s local mode is used.
3. When an object cannot be converted in some mode (global or local), the object fall through to the next mode. The NO_CONVERSION mode always succeed returning a “pure” Robj object.

At startup the default mode is set to NO_DEFAULT, which means that each object has its own conversion mode, and every Robj object is retrieved with a local mode set to PROC_CONVERSION.