Michele Campeotto

One easy example are enumerables/iterables: in Ruby, an object is enumerable if it implements the each method. The object can then mix in Enumerable to gain some methods that you can use:

f = File.new(".bashrc", "r")
lines = f.find_all { |l| l =~ /^[^#]/ }
# or lines = f.grep(/^[^#]/)

In Python, an object is iterable if it implements the __iter__ method, and the language “knows” how to use the iterators:

f = file(".bashrc", "r")
lines = [ l for l in f if not l.startswith("#") ]
# or lines = filter(lambda l: not l.startswith("#"), f)

other examples are any and all, which incidentally are what started the discussion with Francesco about this:

In Ruby, the any? method is added to every enumerable object that mixes in Enumerable:

lines.any? { |l| l =~ /^#/ }

In Python, any() is a built-in function (introduced in 2.5) which knows how to use any sequence:

any(l.startswith("#") for l in lines)

So Ruby works from the inside, and Python from the outside of objects. I think therefore that the next comparison between the two languages should not be side-by-side, but inside-and-out.