[DICT] Add Python support for reversed

[EmilyBourne]

Describe the feature

Syntactic and semantic support should be added for reversed. This should be tested by implementing Python printing

Test Code

Provide code which does not currently work but which should do when this issue is fixed:

def foo():
    a = {1,1.0, 2:2.0}
    b : int[int]
    for bi in reversed(a):
        b.append(bi)
    return a, b

[shoaib-moeen]

Hi @EmilyBourne , I can start working on this. Could you give me a sample output for the above code?

[EmilyBourne]

Hi @shoaib-moeen
For the moment this issue is just about translating Python to Python. We do this as a first step to get the syntactic and semantic stages working before printing in C or Fortran. For the Python support all the issues from #1880-#1890 should be somewhat similar. There is already an open PR for #1886, see #1891. You may want to fork that branch to avoid conflicts/repeat code.
There are also several examples of similar merged PRs for lists and sets. Eg #1798

Just to warn you though. A PR related to this issue is likely to stay open for a few weeks as it will be dependent on my PRs and the person who merges my PRs is not available at the moment

[EmilyBourne]

Hello again @shoaib-moeen , I've had another think about this, this morning. I forget that reversed is a little special compared to other dictionary methods because it is an iterator. The other dictionary methods should be a bit simpler to handle. For reversed you will need to define it similarly to pyccel.ast.itertools.Product. Specifically the equivalent to the following methods will need to be implemented:

pyccel/pyccel/ast/itertoolsext.py

Lines 48 to 63 in d64be7f

	def __getitem__(self, indices):
	return [elem[idx] for idx, elem in zip(indices, self.elements)]
	def to_range(self):
	""" Get the range iterator(s) needed to access all elements of Product
	"""
	lengths = [getattr(e, '__len__',
	getattr(e, 'length', PythonLen(e))) for e in self.elements]
	lengths = [l() if callable(l) else l for l in lengths]
	return [PythonRange(l) for l in lengths]
	@property
	def n_indices(self):
	""" Number of indices required
	"""
	return len(self._elements)

But I'm not sure how the to_range method should be implemented here.

Soon we will add the C implementation. It will be based on STC (https://github.com/stclib/STC/blob/master/docs/smap_api.md). I think the answer about how to implement this is probably related to how this would be written in C but I haven't found anything about reversing the order of things in the docs so far.

[shoaib-moeen]

Thanks @EmilyBourne. I ll look into other issues. Maybe start working on #1887