On 2011-12-10, at 15:16 , Richard Prosser wrote:
A classic example is a mutable default argument having the potential to produce unexpected side-effects, as a consequence of the non-intuitive scoping rules.
As far as I know, mutable default arguments have nothing to do with scoping, they have to do with the "toplevel" being evaluated fully, so as the function declaration is evaluated (to create the function object) so are its default arguments. This is independent from Python's scoping issues unless I misunderstood what you meant by "scoping".
But this is definitely something which trips people. However, there is already a note (though a pretty low-key one, it should probably use an actual warning directive instead of just bolding it, you should submit a documentation patch) in the tutorial on that subject[0].
Another awkward 'feature' is the requirement for a trailing comma in singleton tuples, due I believe to the use of expression parentheses rather than (say) the use of special brackets like chevrons.
For tuples, there are no matching operators left, as literal sets have been added.
And technically, the irregularity with tuples is probably the empty tuple `()` as parens in other tuple arities are only necessary for disambiguation (much like parens around generator expressions): the "tuple constructor" is the comma, not the parens,
a = 1, b = 1, 2 c = 1, 2, 3
are all valid and generate respectively a singleton, a pair and a triple. In that context, the trailing comma for singletons makes sense. If you want regularity, you can even add a trailing comma to the pair and the triple (as you can in e.g. a list or a dict):
a = 1, b = 1, 2, c = 1, 2, 3,
I'd rather have a lone comma (with or without parens, depending on the context) create a null tuple.
Something that I personally wish for is the ability to declare variable types 'up front' but that facility is missing from Python.
I fail to see how this is a "gotcha": since Python is dynamically typed names don't have types (well technically Python 3 added documentary type specs to arguments, but they're not used by any implementation I know of though some third-party tools may already have started using them)
[0] http://docs.python.org/tutorial/controlflow.html#default-argument-values