The PyA guide for porting IDL code

The “Interactive Data Language” (IDL) has been an influential tool in the astronomical community. Some essential code is written in IDL, and sometimes it may be desirable to port it to Python.

Some typical aspects of IDL cannot be directly translated into Python constructs. Therefore, we provide a number of guidelines here, which can be used in porting IDL code to Python:

• Case sensitivity

  IDL is case-insensitive. We recommend to use lower case for all function and variable names.

• IDL keywords

  IDL functions may take keyword arguments. If the purpose of the keyword is only to be present or not, we recommend to use a boolean keyword that defaults to False in Python. If the keyword argument is supposed to convey information to the function, we recommend to use a Python keyword that defaults to the standard value used (in IDL) when when the keyword is not given.

• Arrays

  Python provides no built-in array support. IDL arrays are represented by numpy arrays. Were IDL uses an array as return value, it may not be good practice to do the same in Python. In this case, it remains up to the developer to choose a reasonable solution and document it.

• Functions supporting both single float and array arguments

  We regard array support in Python as optional. In most cases performance is not an issue for the functions under consideration.