Missing wrappers for iterators and generators

[mrkn]

I want to write the following Python code

for item in collection:
  ...

like the following in Ruby with PyCall:

collection.each do |item|
  ...
end

Now PyCall defines each methods in PyCall::List and PyCall::Dict in specific ways. It needs to be rewritten in more generic way.

[mrkn]

One candidate is PyCall.enum(obj) to get an Enumerator object.

This is a concept implementation:

module PyCall
  module_function

  def enum(obj)
    gen = obj.__iter__
    Enumerator.new do |y|
      begin
        yield gen.__next__ while true
        obj
      rescue PyError, err
        # ignore StopIteration exception
        return obj if err.type.match?(LibPython::API::PyExc_StopIteration)
        raise
      end
    end
  end
end

[allomov]

Just one note: I needed to use generator using following function PyCall.builtins.next(generator)

[allomov]

Here is my version of the patch:

module PyCall
  module_function

  def enum(generator)
    Enumerator.new do |enum|
      begin
        loop do
          enum << PyCall.builtins.next(generator)
        end
      rescue PyError => error
        raise err unless error.type.to_s.match?("StopIteration")
      end
    end
  end
end

[mrkn]

@allomov Could you please make a pull-request?