Make PyGoRE Python 2 compatible

[0xThiebaut]

This PR introduces Python 2 compatibility by adding minor statements implicitly covered by Python 3's syntax sugar.

Why support the end-of-life Python 2?

Supporting Python 2 enables PyGoRE to be used in Java-based projects through Jython. This PR is the first step in integrating GoRE into Ghidra. 🎉

[0xThiebaut]

A small mention that leveraging Python 2 to integrate GoRE into Ghidra through the Java Python interpreter (Jython) is not possible. As so, this PR might be closed if Python 2 support is not something that interests the maintainers.

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The PyGoRE bindings cannot be used as Ghidra’s Java Python interpreter (Jython) does not support non-scalar C types in C structures. One of such examples is the following code from PyGoRE’s internal.py.

class _CompilerVersion(Structure):
    _fields_ = [('name', c_char_p),
                ('sha', c_char_p),
                ('timestamp', c_char_p)]

The c_char_p type is defined as follow in Jython’s ctypes.

class c_char_p(jffi.StringCData, _CData):
    _type_ = 'z'
    _jffi_type = jffi.Type.STRING

However, adding fields to a struct does not support non-scalar values as can be seen in Jython’s ctypes.

    def add_field(self, f):
        if not issubclass(f[1], _ScalarCData):
            raise RuntimeError("non-scalar fields not supported")

Integrating GoRE in Ghidra will have to be done through native Java.

[TcM1911]

Thank you for contributing. I'm a bit hesitant to add support for an EOL version of a language. Would it be possible to integrate support with Ghidra by using the c-library shim?

[0xThiebaut]

Not exactly as Java can't call C libraries if they haven't been build explicitly for Java using the JNI specification (See JNIEXPORT and JNICALL macros).

Anyway, as Python is off the table anyway, I'll close this PR.