I am surprised that no one has mentioned Singleton methods.
a=[]
b=[]
def b.some_method do ... end
b.some_method #fine
a.some_method #raises exception
It gives granular control over the open class concept. You can also use Eigenclasses to mixin a module into a specific object instead of all objects of a given class.
o=Object.new
class << o
include SomeModule
end
Python also doesn't have a switch statement without using ugly hacks which can decrease code readability.
Ruby has no statements,only expressions. This add a lot of flexibility.
You can get a reference to any method and pass that around.
a=[]
m=a.method :map #m is now referencing an instance of Method and can be passed like any other reference to an object and is invoked with the call method and an optional block
Easy nested lexical scope giving controlled global variables.
lambda {
global=nil
def Kernel.some_global= val
global||=val
end
def Kernel.some_global
global
end
}.call
Once that lambda is invoked, global is out of scope, but you can set it(only once in this example) and then access it anywhere in your program. Hopefully the value of this is clear.
Creating a DSL is much easier in Ruby than in Python. Creating something like Rake or RSpec in Python is possible but what a nightmare it would be. So to answer your question Ruby has much more flexibility than Python. It is not at the flexibility level of Lisp, but is arguably the most flexible OO language.
Python is great and all but it is so stiff compared to Ruby. Ruby is less verbose, more readable(as in it reads much closer to a natural language), python reads like english translated to french.
Python is also annoying in that its community is always in lock-step with Guido, if Guido says that you don't need feature X, everyone in the community believes it and parrots it. It leads to a stale community, kind of like the Java community that simply can't understand what anonymous functions and closures buy you. The Python community is not as annoying as Haskell's, but still.