Converters_module

Convert Casacore objects to/from Python (using Boost.Python) More...

Modules
	Converters_module_internal_classes
	Internal Converters_module classes and functions.

Classes
struct	casacore::python::casa_record_to_python
	A class to convert a (Table)Record to/from Python objects. More...
struct	casacore::python::casa_value_to_python
	A class to convert a ValueHolder to/from Python objects. More...

Functions
Bool	casacore::python::PycArrayCheck (PyObject *obj_ptr)
	A class to convert an Array to/from Python objects. More...

Detailed Description

Convert Casacore objects to/from Python (using Boost.Python)

See below for an overview of the classes in this module.

Intended use:

Public interface

Review Status

Test programs:

tConvert

Prerequisite

• Record class
• Record class

Synopsis

Converters contains functions to convert the important Casacore objects to/from Python using the Boost.Python package. Converters for the following Casacore classes exist:

• Scalars of basic data types like Bool, Int, Float, Complex.
• casacore::String and std::string.
• casacore::Vector and std::vector of any type which can be converted from a Python scalar, list, tuple, or 1-dim array. They are converted back to a Python list.
• Record which is converted to/from a Python dict.
• ValueHolder which is converted to/from the appropriate Python type. A ValueHolder is a class which can hold various value types:
  • Scalar of any basic data type.
  • Record.
  • N-dim Array of any basic data type. A casacore::Array can be constructed from Python types like tuple, list, and numpy array A Py_None object results in an empty array. The conversion back is done to a numpy array. An empty array is returned as an empty numpy array.
    Because Casacore arrays are in Fortran order and numpy arrays (preferably) in C order, the axes are reversed during conversion.
    A 1-dim Array<String> object is converted to a list, while a higher dimensioned Array<String> object is converted to/from a dict containing the shape and the values as a list. However, conversion from a numpy string array is supported.
  A ValueHolder is for instance used by the Table System to be able to get or put data in a column of any type. It can be used by any Python binding to convert arrays. Class ValueHolder has functions to get or set the array.
• casacore::IPosition which can be converted from a Python scalar, list, tuple, or 1-dim array. It is converted back to a Python list. An IPosition object represents an array shape or position, so its values are reversed because of the different ordening of Casacore and Python arrays.
• Exceptions, which are mapped to a Python RuntimeError exception. Only the casacore::IterError exception is mapped to a Python StopIteration exception.

The converts from Python to C++ can handle some special numpy objects. Such objects can also be contained in sequences or dicts.

• Elements in a numpy array are called array scalars. They do not have a python type such as int, but instead a type as numpy.int32. The converters can handle such types and convert them correctly to a scalar.
• A numpy scalar array (e.g. array(1.0) is a somewhat peculiar numpy object. It has an empty shape and cannot be indexed. It is handled correctly by the from converters and handled as a scalar value.
• An empty numpy object (e.g. array([])) is handled as a None value.

Function Documentation

Bool casacore::python::PycArrayCheck

(

PyObject *

obj_ptr

)

A class to convert an Array to/from Python objects.

Intended use:

Public interface

Synopsis

Check if the PyObject is an array object.

Definition at line 35 of file PycArrayComCC.h.

Referenced by makeArray().