Put py: Python argument at beginning or end of argument list?

[dgrunwald]

Now that #15 is adding a py: Python argument to almost every function, we should pick a consistent position for that argument.

Beginning: fn(Python, ...)
End: fn(..., Python)

Calls seem more readable to me in the beginning position:
some_method(py, nested_call(py, long, argument, list))
vs.
some_method(nested_call(long, argument, list, py), py)

If we want the non-Copy Python token, and use the beginning position, nested calls will fail to compile with Rust's current reborrowing semantics. This might or might not be fixed in a future Rust version.

However, there are good reasons for Python to remain Copy, so I think the beginning position is the correct choice.

[ehiggs]

Beginning.