IDL-to-Python Mapping Plan

Primitive Types

• IDL boolean maps to Python bool.

• All IDL integer types map to Python int.

  • During serialization, if the value it does not fit in the types range, raise a ValueError.

• IDL float and double map to Python float. IDL long double and fixed map to Python decimal.Decimal.

Character Types

All IDL characters and strings map to Python str.

Unlike C strings, Python str requires the encoding to be known. To help facilitate this, by default characters and strings will be assumed to be UTF-8 and wide characters and strings will be assumed to be UTF-16. The encoding will be able to be specified either using a global implementation option or manually using this IDL annotation:

@annotion encoding {
    string platform default "*";
    string value;
};

For Python, platform can be left to default or set to python and value should be a valid Python codec. Here is the list of codecs for Python 3.7. As an example, if you wanted to use ISO-8859-10 “on the wire”, you could write something like this:

struct Data {
    @encoding(platform="python", value="latin6")
    string put_swedish_here;
};

During serialization and deserialization, encoding will be handled automatically, but will be subject to UnicodeError if there is a problem with the encoding.

Alternatively value can be set to "none" to represent that no automatic encoding and decoding should be done. This is probably the behavior many other IDL mappings and would probably be the default if the annotation was adopted in other implementation. For Python this will change the type from str to bytes, which better represents the idea of string of bytes of uncertain encoding.

During serialization, raise a ValueError if the size of the encoded data is larger than the limits of the IDL type. For example: assigning Python "more than a byte" to a IDL field of type char.

Composite Types

• IDL arrays and sequences map to Python list

  • During serialization, if the IDL type is an array or bounded sequence, raise ValueError if the element count of the list is out of the valid range.

• IDL structures map to Python dataclasses or equivalent.

• IDL enum map to Python enum.IntFlag

Unions

This IDL:

enum EnumType {
    A, B, C
};

union UnionType switch (EnumType) {
case A:
    long number;
case B:
case C:
    char character;
};

Will produce Python like:

class UnionType:
    def __init__(self):
        self._d = None

    @property
    def number(self):
        if self._d != EmunType.A:
            raise # TODO What kind of Error does this need to be?
        return self._number

    @number.setter
    def number(self, value: int):
        self._d = EnumType.A
        self._number = value