What does Ruby have that Python doesn't, and vice versa?

Ruby has the concepts of blocks, which are essentially syntactic sugar around a section of code; they are a way to create closures and pass them to another method which may or may not use the block. A block can be invoked later on through a yield statement.

For example, a simple definition of an each method on Array might be something like:

class Array
  def each
    for i in self  
      yield(i)     # If a block has been passed, control will be passed here.
    end  
  end  
end  

Then you can invoke this like so:

# Add five to each element.
[1, 2, 3, 4].each{ |e| puts e + 5 }
> [6, 7, 8, 9]

Python has anonymous functions/closures/lambdas, but it doesn’t quite have blocks since it’s missing some of the useful syntactic sugar. However, there’s at least one way to get it in an ad-hoc fashion. See, for example, here.

Python has docstrings and ruby doesn’t… Or if it doesn’t, they are not accessible as easily as in python.

Ps. If im wrong, pretty please, leave an example? I have a workaround that i could monkeypatch into classes quite easily but i’d like to have docstring kinda of a feature in “native way”.

What Ruby has over Python are its scripting language capabilities. Scripting language in this context meaning to be used for “glue code” in shell scripts and general text manipulation.

These are mostly shared with Perl. First-class built-in regular expressions, $-Variables, useful command line options like Perl (-a, -e) etc.

Together with its terse yet epxressive syntax it is perfect for these kind of tasks.

Python to me is more of a dynamically typed business language that is very easy to learn and has a neat syntax. Not as “cool” as Ruby but neat.
What Python has over Ruby to me is the vast number of bindings for other libs. Bindings to Qt and other GUI libs, many game support libraries and and and. Ruby has much less. While much used bindings e.g. to Databases are of good quality I found niche libs to be better supported in Python even if for the same library there is also a Ruby binding.

So, I’d say both languages have its use and it is the task that defines which one to use. Both are easy enough to learn. I use them side-by-side. Ruby for scripting and Python for stand-alone apps.

While the functionalty is to a great extent the same (especially in the Turing sense), malicious tongues claim that Ruby was created for Pythonistas that could not split up with the Perlish coding style.

I don’t think “Ruby has X and Python doesn’t, while Python has Y and Ruby doesn’t” is the most useful way to look at it. They’re quite similar languages, with many shared abilities.

To a large degree, the difference is what the language makes elegant and readable. To use an example you brought up, both do theoretically have lambdas, but Python programmers tend to avoid them, and constructs made using them do not look anywhere near as readable or idiomatic as in Ruby. So in Python, a good programmer will want to take a different route to solving the problem than he would in Ruby, just because it actually is the better way to do it.

Python has a “we’re all adults here” mentality. Thus, you’ll find that Ruby has things like constants while Python doesn’t (although Ruby’s constants only raise a warning). The Python way of thinking is that if you want to make something constant, you should put the variable names in all caps and not change it.

For example, Ruby:

>> PI = 3.14
=> 3.14
>> PI += 1
(irb):2: warning: already initialized constant PI
=> 4.14

Python:

>>> PI = 3.14
>>> PI += 1
>>> PI
4.1400000000000006

Ruby has sigils and twigils, Python doesn’t.

Edit: And one very important thing that I forgot (after all, the previous was just to flame a little bit :-p):

Python has a JIT compiler (Psyco), a sightly lower level language for writing faster code (Pyrex) and the ability to add inline C++ code (Weave).

Ruby has builtin continuation support using callcc.

Hence you can implement cool things like the amb-operator

Python has an explicit, builtin syntax for list-comprehenions and generators whereas in Ruby you would use map and code blocks.

Compare

list = [ x*x for x in range(1, 10) ]

to

res = (1..10).map{ |x| x*x }

I’m unsure of this, so I add it as an answer first.

Python treats unbound methods as functions

That means you can call a method either like theobject.themethod() or by TheClass.themethod(anobject).

Edit: Although the difference between methods and functions is small in Python, and non-existant in Python 3, it also doesn’t exist in Ruby, simply because Ruby doesn’t have functions. When you define functions, you are actually defining methods on Object.

But you still can’t take the method of one class and call it as a function, you would have to rebind it to the object you want to call on, which is much more obstuse.

Some others from:

http://www.ruby-lang.org/en/documentation/ruby-from-other-languages/to-ruby-from-python/

(If I have misintrepreted anything or any of these have changed on the Ruby side since that page was updated, someone feel free to edit…)

Strings are mutable in Ruby, not in Python (where new strings are created by “changes”).

Ruby has some enforced case conventions, Python does not.

Python has both lists and tuples (immutable lists). Ruby has arrays corresponding to Python lists, but no immutable variant of them.

In Python, you can directly access object attributes. In Ruby, it’s always via methods.

In Ruby, parentheses for method calls are usually optional, but not in Python.

Ruby has public, private, and protected to enforce access, instead of Python’s convention of using underscores and name mangling.

Python has multiple inheritance. Ruby has “mixins.”

And another very relevant link:

http://c2.com/cgi/wiki?PythonVsRuby

Which, in particular, links to another good one by Alex Martelli, who’s been also posting a lot of great stuff here on SO:

http://groups.google.com/group/comp.lang.python/msg/028422d707512283

You can import only specific functions from a module in Python. In Ruby, you import the whole list of methods. You could “unimport” them in Ruby, but it’s not what it’s all about.

EDIT:

let’s take this Ruby module :

module Whatever
  def method1
  end

  def method2
  end
end

if you include it in your code :

include Whatever

you’ll see that both method1 and method2 have been added to your namespace. You can’t import only method1. You either import them both or you don’t import them at all. In Python you can import only the methods of your choosing. If this would have a name maybe it would be called selective importing?

Ruby has a line by line loop over input files (the ‘-n’ flag) from the commandline so it can be used like AWK. This Ruby one-liner:

ruby -ne 'END {puts $.}'

will count lines like the AWK one-liner:

awk 'END{print NR}'

Ruby gets feature this through Perl, which took it from AWK as a way of getting sysadmins on board with Perl without having to change the way they do things.

Python Example

Functions are first-class variables in Python. You can declare a function, pass it around as an object, and overwrite it:

def func(): print "hello"
def another_func(f): f()
another_func(func)

def func2(): print "goodbye"
func = func2

This is a fundamental feature of modern scripting languages. JavaScript and Lua do this, too. Ruby doesn’t treat functions this way; naming a function calls it.

Of course, there are ways to do these things in Ruby, but they’re not first-class operations. For example, you can wrap a function with Proc.new to treat it as a variable–but then it’s no longer a function; it’s an object with a “call” method.

Ruby’s functions aren’t first-class objects

Ruby functions aren’t first-class objects. Functions must be wrapped in an object to pass them around; the resulting object can’t be treated like a function. Functions can’t be assigned in a first-class manner; instead, a function in its container object must be called to modify them.

def func; p "Hello" end
def another_func(f); method(f)[] end
another_func(:func)      # => "Hello"

def func2; print "Goodbye!"
self.class.send(:define_method, :func, method(:func2))
func                     # => "Goodbye!"

method(:func).owner      # => Object
func                     # => "Goodbye!"
self.func                # => "Goodbye!"    

python has named optional arguments

def func(a, b=2, c=3):
    print a, b, c

>>> func(1)
1 2 3
>>> func(1, c=4)
1 2 4

AFAIK Ruby has only positioned arguments because b=2 in the function declaration is an affectation that always append.

“Variables that start with a capital letter becomes constants and can’t be modified”

Wrong. They can.

You only get a warning if you do.

I would like to mention Python descriptor API that allows one customize object-to-attribute “communication”. It is also noteworthy that, in Python, one is free to implement an alternative protocol via overriding the default given through the default implementation of the __getattribute__ method.
Let me give more details about the aforementioned.
Descriptors are regular classes with __get__, __set__ and/or __delete__ methods.
When interpreter encounters something like anObj.anAttr, the following is performed:

• __getattribute__ method of anObj is invoked
• __getattribute__ retrieves anAttr object from the class dict
• it checks whether abAttr object has __get__, __set__ or __delete__ callable objects
• the context (i.e., caller object or class, and value, instead of the latter, if we have setter) is passed to the callable object
• the result is returned.

As was mentioned, this is the default behavior. One is free to change the protocol by re-implementing __getattribute__.

This technique is lot more powerful than decorators.

Surprised to see nothing mentioned of ruby’s “method missing” mechanism. I’d give examples of the find_by_… methods in Rails, as an example of the power of that language feature. My guess is that something similar could be implemented in Python, but to my knowledge it isn’t there natively.

Ruby has embedded documentation:

 =begin

 You could use rdoc to generate man pages from this documentation

 =end

My python’s rusty, so some of these may be in python and i just don’t remember/never learned in the first place, but here are the first few that I thought of:

Whitespace

Ruby handles whitespace completely different. For starters, you don’t need to indent anything (which means it doesn’t matter if you use 4 spaces or 1 tab). It also does smart line continuation, so the following is valid:

def foo(bar,
        cow)

Basically, if you end with an operator, it figures out what is going on.

Mixins

Ruby has mixins which can extend instances instead of full classes:

module Humor
  def tickle
    "hee, hee!"
  end
end
a = "Grouchy"
a.extend Humor
a.tickle    »   "hee, hee!"

Enums

I’m not sure if this is the same as generators, but as of Ruby 1.9 ruby as enums, so

>> enum = (1..4).to_enum
=> #<Enumerator:0x1344a8>

Reference: http://blog.nuclearsquid.com/writings/ruby-1-9-what-s-new-what-s-changed

“Keyword Arguments”

Both of the items listed there are supported in Ruby, although you can’t skip default values like that.
You can either go in order

def foo(a, b=2, c=3)
  puts "#{a}, #{b}, #{c}"
end
foo(1,3)   >> 1, 3, 3
foo(1,c=5) >> 1, 5, 3
c          >> 5

Note that c=5 actually assigns the variable c in the calling scope the value 5, and sets the parameter b the value 5.

or you can do it with hashes, which address the second issue

def foo(a, others)
  others[:b] = 2 unless others.include?(:b)
  others[:c] = 3 unless others.include?(:c)
  puts "#{a}, #{others[:b]}, #{others[:c]}"
end
foo(1,:b=>3) >> 1, 3, 3
foo(1,:c=>5) >> 1, 2, 5

Reference: The Pragmatic Progammer’s Guide to Ruby

I’d like to suggest a variant of the original question, “What does Ruby have that Python doesn’t, and vice versa?” which admits the disappointing answer, “Well, what can you do with either Ruby or Python that can’t be done in Intercal?” Nothing on that level, because Python and Ruby are both part of the vast royal family sitting on the throne of being Turing approximant.

But what about this:

What can be done gracefully and well in Python that can’t be done in Ruby with such beauty and good engineering, or vice versa?

That may be much more interesting than mere feature comparison.

From Ruby’s website:

Similarities
As with Python, in Ruby,…

• There’s an interactive prompt (called irb).
• You can read docs on the command line (with the ri command instead of pydoc).
• There are no special line terminators (except the usual newline).
• String literals can span multiple lines like Python’s triple-quoted strings.
• Brackets are for lists, and braces are for dicts (which, in Ruby, are called “hashes”).
• Arrays work the same (adding them makes one long array, but composing them like this a3 = [ a1, a2 ] gives you an array of arrays).
• Objects are strongly and dynamically typed.
• Everything is an object, and variables are just references to objects.
• Although the keywords are a bit different, exceptions work about the same.
• You’ve got embedded doc tools (Ruby’s is called rdoc).

Differences
Unlike Python, in Ruby,…

• Strings are mutable.
• You can make constants (variables whose value you don’t intend to change).
• There are some enforced case-conventions (ex. class names start with a capital letter, variables start with a lowercase letter).
• There’s only one kind of list container (an Array), and it’s mutable.
• Double-quoted strings allow escape sequences (like t) and a special “expression substitution” syntax (which allows you to insert the results of Ruby expressions directly into other strings without having to “add ” + “strings ” + “together”). Single-quoted strings are like Python’s r”raw strings”.
• There are no “new style” and “old style” classes. Just one kind.
• You never directly access attributes. With Ruby, it’s all method calls.
• Parentheses for method calls are usually optional.
• There’s public, private, and protected to enforce access, instead of Python’s _voluntary_ underscore __convention__.
• “mixin’s” are used instead of multiple inheritance.
• You can add or modify the methods of built-in classes. Both languages let you open up and modify classes at any point, but Python prevents modification of built-ins — Ruby does not.
• You’ve got true and false instead of True and False (and nil instead of None).
• When tested for truth, only false and nil evaluate to a false value. Everything else is true (including 0, 0.0, “”, and []).
• It’s elsif instead of elif.
• It’s require instead of import. Otherwise though, usage is the same.
• The usual-style comments on the line(s) above things (instead of docstrings below them) are used for generating docs.
• There are a number of shortcuts that, although give you more to remember, you quickly learn. They tend to make Ruby fun and very productive.

Somewhat more on the infrastructure side:

• Python has much better integration with C++ (via things like Boost.Python, SIP, and Py++) than Ruby, where the options seem to be either write directly against the Ruby interpreter API (which you can do with Python as well, of course, but in both cases doing so is low level, tedious, and error prone) or use SWIG (which, while it works and definitely is great if you want to support many languages, isn’t nearly as nice as Boost.Python or SIP if you are specifically looking to bind C++).

• Python has a number of web application environments (Django, Pylons/Turbogears, web.py, probably at least half a dozen others), whereas Ruby (effectively) has one: Rails. (Other Ruby web frameworks do exist, but seemingly have a hard time getting much traction against Rails). Is this aspect good or bad? Hard to say, and probably quite subjective; I can easily imagine arguments that the Python situation is better and that the Ruby situation is better.

• Culturally, the Python and Ruby communities seem somewhat different, but I can only hint at this as I don’t have that much experience interacting with the Ruby community. I’m adding this mostly in the hopes that someone who has a lot of experience with both can amplify (or reject) this statement.

Another difference in lambdas between Python and Ruby is demonstrated by Paul Graham’s Accumulator Generator problem. Reprinted here:

Write a function foo that takes a number n and returns a function that takes a number i, and returns n incremented by i.

Note: (a) that’s number, not integer, (b) that’s incremented by, not plus.

In Ruby, you can do this:

def foo(n)
  lambda {|i| n += i }
end

In Python, you’d create an object to hold the state of n:

class foo(object):
    def __init__(self, n):
        self.n = n
    def __call__(self, i):
        self.n += i
        return self.n

Some folks might prefer the explicit Python approach as being clearer conceptually, even if it’s a bit more verbose. You store state like you do for anything else. You just need to wrap your head around the idea of callable objects. But regardless of which approach one prefers aesthetically, it does show one respect in which Ruby lambdas are more powerful constructs than Python’s.

http://c2.com/cgi/wiki?PythonVsRuby
http://c2.com/cgi/wiki?SwitchedFromPythonToRuby
http://c2.com/cgi/wiki?SwitchedFromRubyToPython
http://c2.com/cgi/wiki?UsingPythonDontNeedRuby
http://c2.com/cgi/wiki?UsingRubyDontNeedPython

_{Shamelessly copy/pasted from: Alex Martelli answer on “What’s better about Ruby than Python“ thread from comp.lang.python mailing list.}

Aug 18 2003, 10:50 am Erik Max Francis
wrote:

“Brandon J. Van Every” wrote:

What’s better about Ruby than Python? I’m sure there’s something.
What is it?

Wouldn’t it make much more sense to ask Ruby people this, rather than
Python people?

Might, or might not, depending on
one’s purposes — for example, if
one’s purposes include a “sociological
study” of the Python community, then
putting questions to that community is
likely to prove more revealing of
information about it, than putting
them elsewhere:-).

Personally, I gladly took the
opportunity to follow Dave Thomas’
one-day Ruby tutorial at last OSCON.
Below a thin veneer of syntax
differences, I find Ruby and Python
amazingly similar — if I was
computing the minimum spanning tree
among just about any set of languages,
I’m pretty sure Python and Ruby would
be the first two leaves to coalesce
into an intermediate node:-).

Sure, I do get weary, in Ruby, of
typing the silly “end” at the end of
each block (rather than just
unindenting) — but then I do get to
avoid typing the equally-silly ‘:’
which Python requires at the
start of each block, so that’s almost a wash:-). Other syntax
differences such as ‘@foo’ versus
‘self.foo’, or the higher significance
of case in Ruby vs Python, are really
just about as irrelevant to me.

Others no doubt base their choice of
programming languages on just such
issues, and they generate the hottest
debates — but to me that’s just an
example of one of Parkinson’s Laws in
action (the amount on debate on an
issue is inversely proportional to the
issue’s actual importance).

Edit (by AM 6/19/2010 11:45): this is also known as “painting the
bikeshed” (or, for short,
“bikeshedding”) — the reference is,
again, to Northcote Parkinson, who
gave “debates on what color to paint
the bikeshed” as a typical example of
“hot debates on trivial topics”.
(end-of-Edit).

One syntax difference that I do find
important, and in Python’s favor —
but other people will no doubt think
just the reverse — is “how do you
call a function which takes no
parameters”. In Python (like in C),
to call a function you always apply
the “call operator” — trailing
parentheses just after the object
you’re calling (inside those trailing
parentheses go the args you’re passing
in the call — if you’re passing no
args, then the parentheses are empty).
This leaves the mere mention of
any object, with no operator involved, as meaning just a reference
to the object — in any context,
without special cases, exceptions,
ad-hoc rules, and the like. In Ruby
(like in Pascal), to call a function
WITH arguments you pass the args
(normally in parentheses, though that
is not invariably the case) — BUT if
the function takes no args then simply
mentioning the function implicitly
calls it. This may meet the
expectations of many people (at least,
no doubt, those whose only previous
experience of programming was with
Pascal, or other languages with
similar “implicit calling”, such as
Visual Basic) — but to me, it means
the mere mention of an object may
EITHER mean a reference to the object,
OR a call to the object, depending on
the object’s type — and in those
cases where I can’t get a reference to
the object by merely mentioning it I
will need to use explicit “give me a
reference to this, DON’T call it!”
operators that aren’t needed
otherwise. I feel this impacts the
“first-classness” of functions (or
methods, or other callable objects)
and the possibility of interchanging
objects smoothly. Therefore, to me,
this specific syntax difference is a
serious black mark against Ruby — but
I do understand why others would thing
otherwise, even though I could hardly
disagree more vehemently with them:-).

Below the syntax, we get into some
important differences in elementary
semantics — for example, strings in
Ruby are mutable objects (like in
C++), while in Python they are not
mutable (like in Java, or I believe
C#). Again, people who judge
primarily by what they’re already
familiar with may think this is a plus
for Ruby (unless they’re familiar with
Java or C#, of course:-). Me, I think
immutable strings are an excellent
idea (and I’m not surprised that Java,
independently I think, reinvented that
idea which was already in Python),
though I wouldn’t mind having a
“mutable string buffer” type as well
(and ideally one with better
ease-of-use than Java’s own “string
buffers”); and I don’t give this
judgment because of familiarity —
before studying Java, apart from
functional programming languages where
all data are immutable, all the languages I knew had mutable strings
— yet when I first saw the immutable-string idea in Java (which I
learned well before I learned Python),
it immediately struck me as excellent,
a very good fit for the
reference-semantics of a higher level
programming language (as opposed to
the value-semantics that fit best with
languages closer to the machine and
farther from applications, such as C)
with strings as a first-class,
built-in (and pretty crucial) data
type.

Ruby does have some advantages in
elementary semantics — for example,
the removal of Python’s “lists vs
tuples” exceedingly subtle
distinction. But mostly the score (as
I keep it, with simplicity a big plus
and subtle, clever distinctions a
notable minus) is against Ruby (e.g.,
having both closed and half-open
intervals, with the notations a..b and
a…b [anybody wants to claim that
it’s obvious which is which?-)], is
silly — IMHO, of course!). Again,
people who consider having a lot of
similar but subtly different things at
the core of a language a PLUS, rather
than a MINUS, will of course count
these “the other way around” from how
I count them:-).

Don’t be misled by these comparisons
into thinking the two languages are
very different, mind you. They aren’t. But if I’m asked to compare
“capelli d’angelo” to “spaghettini”,
after pointing out that these two
kinds of pasta are just about
undistinguishable to anybody and
interchangeable in any dish you might
want to prepare, I would then
inevitably have to move into
microscopic examination of how the
lengths and diameters imperceptibly
differ, how the ends of the strands
are tapered in one case and not in the
other, and so on — to try and explain
why I, personally, would rather have
capelli d’angelo as the pasta in any
kind of broth, but would prefer
spaghettini as the pastasciutta to go
with suitable sauces for such long
thin pasta forms (olive oil, minced
garlic, minced red peppers, and finely
ground anchovies, for example – but if
you sliced the garlic and peppers
instead of mincing them, then you
should choose the sounder body of
spaghetti rather than the thinner
evanescence of spaghettini, and would
be well advised to forego the achovies
and add instead some fresh spring
basil [or even — I’m a heretic…! —
light mint…] leaves — at the very
last moment before serving the dish).
Ooops, sorry, it shows that I’m
traveling abroad and haven’t had pasta
for a while, I guess. But the analogy
is still pretty good!-)

So, back to Python and Ruby, we come
to the two biggies (in terms of
language proper — leaving the
libraries, and other important
ancillaries such as tools and
environments, how to embed/extend each
language, etc, etc, out of it for now
— they wouldn’t apply to all IMPLEMENTATIONS of each language
anyway, e.g., Jython vs Classic Python
being two implementations of the
Python language!):

1. Ruby’s iterators and codeblocks vs Python’s iterators and generators;

2. Ruby’s TOTAL, unbridled “dynamicity”, including the ability
   to “reopen” any existing class,
   including all built-in ones, and
   change its behavior at run-time — vs
   Python’s vast but bounded
   dynamicity, which never changes the
   behavior of existing built-in
   classes and their instances.

Personally, I consider 1 a wash (the
differences are so deep that I could
easily see people hating either
approach and revering the other, but
on MY personal scales the pluses and
minuses just about even up); and 2 a
crucial issue — one that makes Ruby
much more suitable for “tinkering”,
BUT Python equally more suitable for
use in large production applications.
It’s funny, in a way, because both
languages are so MUCH more dynamic
than most others, that in the end the
key difference between them from my
POV should hinge on that — that Ruby
“goes to eleven” in this regard (the
reference here is to “Spinal Tap”, of
course). In Ruby, there are no limits
to my creativity — if I decide that
all string comparisons must become
case-insensitive, I CAN DO THAT!
I.e., I can dynamically alter the
built-in string class so that
a = “Hello World”
b = “hello world”
if a == b
print “equal!n”
else
print “different!n”
end WILL print “equal”. In python, there is NO way I can do that.
For the purposes of metaprogramming,
implementing experimental frameworks,
and the like, this amazing dynamic
ability of Ruby is extremely
appealing. BUT — if we’re talking
about large applications, developed by
many people and maintained by even
more, including all kinds of libraries
from diverse sources, and needing to
go into production in client sites…
well, I don’t WANT a language that is
QUITE so dynamic, thank you very much.
I loathe the very idea of some library
unwittingly breaking other unrelated
ones that rely on those strings being
different — that’s the kind of deep
and deeply hidden “channel”, between
pieces of code that LOOK separate and
SHOULD BE separate, that spells
d-e-a-t-h in large-scale programming.
By letting any module affect the
behavior of any other “covertly”, the
ability to mutate the semantics of
built-in types is just a BAD idea for
production application programming,
just as it’s cool for tinkering.

If I had to use Ruby for such a large
application, I would try to rely on
coding-style restrictions, lots of
tests (to be rerun whenever ANYTHING
changes — even what should be totally
unrelated…), and the like, to
prohibit use of this language feature.
But NOT having the feature in the
first place is even better, in my
opinion — just as Python itself would
be an even better language for
application programming if a certain
number of built-ins could be “nailed
down”, so I KNEW that, e.g.,
len(“ciao”) is 4 (rather than having
to worry subliminally about whether
somebody’s changed the binding of name
‘len’ in the builtins module…).
I do hope that eventually Python does
“nail down” its built-ins.

But the problem’s minor, since
rebinding built-ins is quite a
deprecated as well as a rare practice
in Python. In Ruby, it strikes me as
major — just like the too powerful
macro facilities of other languages
(such as, say, Dylan) present similar
risks in my own opinion (I do hope
that Python never gets such a powerful
macro system, no matter the allure of
“letting people define their own
domain-specific little languages
embedded in the language itself” — it
would, IMHO, impair Python’s wonderful
usefulness for application
programming, by presenting an
“attractive nuisance” to the would-be
tinkerer who lurks in every
programmer’s heart…).

Alex

In Ruby, when you import a file with
require, all the things defined in
that file will end up in your global
namespace.

With Cargo you can “require libraries without cluttering your namespace“.

# foo-1.0.0.rb
class Foo
  VERSION = "1.0.0"
end

# foo-2.0.0.rb
class Foo
  VERSION = "2.0.0"
end

>> Foo1 = import("foo-1.0.0")
>> Foo2 = import("foo-2.0.0")
>> Foo1::VERSION
=> "1.0.0"
>> Foo2::VERSION
=> "2.0.0"

At this stage, Python still has better unicode support

Ultimately all answers are going to be subjective at some level, and the answers posted so far pretty much prove that you can’t point to any one feature that isn’t doable in the other language in an equally nice (if not similar) way, since both languages are very concise and expressive.

I like Python’s syntax. However, you have to dig a bit deeper than syntax to find the true beauty of Ruby. There is zenlike beauty in Ruby’s consistency. While no trivial example can possibly explain this completely, I’ll try to come up with one here just to explain what I mean.

Reverse the words in this string:

sentence = "backwards is sentence This"

When you think about how you would do it, you’d do the following:

1. Split the sentence up into words
2. Reverse the words
3. Re-join the words back into a string

In Ruby, you’d do this:

sentence.split.reverse.join ' '

Exactly as you think about it, in the same sequence, one method call after another.

In python, it would look more like this:

" ".join(reversed(sentence.split()))

It’s not hard to understand, but it doesn’t quite have the same flow. The subject (sentence) is buried in the middle. The operations are a mix of functions and object methods. This is a trivial example, but one discovers many different examples when really working with and understanding Ruby, especially on non-trivial tasks.

I like the fundamental differences in the way that Ruby and Python method invocations operate.

Ruby methods are invoked via a form “message passing” and need not be explicitly first-class functions (there are ways to lift methods into “proper” function-objects) — in this aspect Ruby is similar to Smalltalk.

Python works much more like JavaScript (or even Perl) where methods are functions which are invoked directly (there is also stored context information, but…)

While this might seem like a “minor” detail it is really just the surface of how different the Ruby and Python designs are. (On the other hand, they are also quite the same 🙂

One practical difference is the concept of method_missing in Ruby (which, for better or worse, seems to be used in some popular frameworks). In Python, one can (at least partially) emulate the behavior using __getattr__/__getattribute__, albeit non-idiomatically.

Ruby gets inheritance right with Single Inheritance

Did I mention Ruby has an EPIC community of developers. Ninja theme inspired by Object Oriented Ruby: Classes, Mixins and Jedi.

Ruby gets inheritance right with Single Inheritance! Needing to use multiple inheritance to express domain relationships is a symptom of an improperly designed system. The confusion multiple inheritance creates isn’t worth the added functionality.

Say you have a method called kick:

def kick
  puts "kick executed."
end

What if kick is defined in both class Ninjutsu and class Shaolin? Multiple Inheritance fails here and that’s why Python fails:

class Mortal < Ninjutsu, Shaolin
  def initialize
    puts "mortal pwnage."
  end
end

In Ruby if you need a Ninja, you create an instance of the Ninja class. If you need a Shaolin master, you create an instance of the Shaolin class.

ninja = Ninjutsu.new
ninja.kick

or 

master = Shaolin.new
master.kick

Ruby gets inheritance right with Mixins

There might be the off chance that both a Ninja and a Shaolin master share the same kick technique. Read that again – both share the same behavior – nothing else! Python would encourage you to roll a whole new class. Not with Ruby! In Ruby you simply use a Mixin:

module Katas
  def kick
    puts "Temporal Whip Kick."
  end
end

and simply Mixin the Katas module into your Ruby Class:

require 'Katas'

class Moral < Ninjutsu
  include Katas

  def initialize
    puts "mortal pwnage."
  end
end

Then the behavior gets shared – which is what you were really going for. Not an entire class. That’s the biggest difference between Ruby and Python – Ruby gets inheritance right!

Syntax is not a minor thing, it has a direct impact on how we think. It also has a direct effect on the rules we create for the systems we use. As an example we have the order of operations because of the way we write mathematical equations or sentences. The standard notation for mathematics allows people to read it more than one way and arrive at different answers given the same equation. If we had used prefix or postfix notation we would have created rules to distinguish what the numbers to be manipulated were rather than only having rules for the order in which to compute values.

The standard notation makes it plain what numbers we are talking about while making the order in which to compute them ambiguous. Prefix and postfix notation make the order in which to compute plain while making the numbers ambiguous. Python would already have multiline lambdas if it were not for the difficulties caused by the syntactic whitespace. (Proposals do exist for pulling this kind of thing off without necessarily adding explicit block delimiters.)

I find it easier to write conditions where I want something to occur if a condition is false much easier to write with the unless statement in Ruby than the semantically equivalent “if-not” construction in Ruby or other languages for example. If most of the languages that people are using today are equal in power, how can the syntax of each language be considered a trivial thing? After specific features like blocks and inheritance mechanisms etc. syntax is the most important part of a language,hardly a superficial thing.

What is superficial are the aesthetic qualities of beauty that we ascribe to syntax. Aesthetics have nothing to do with how our cognition works, syntax does.

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.

The nested lexical scope example that someone gave gives several benefits.

1. “Safer” globals
2. It is one method to embed DSL’s into your program.

I think that is a very good example of the differences between the two languages. Ruby is simply more flexible. Python can be flexible, but you often have to do extreme contortions to get there, which makes it not worth the hassle.

Sorry for not posting under the original answer, I guess I don’t have privileges to do that.

More about Ruby’s blocks

It has being suggested that Ruby’s blocks may be “substituted” by Python’s context managers. In fact, blocks allow more than Python’s context managers can do.

The receiving method of a block could execute the block within the context of some object, thus allowing the block to call methods otherwise unreacheable. Python’s generators can’t do that either.

A simple example may help:

class Proxy
   attr_accesor :target

   def method &block
      # Ruby 1.9 or in Rails 2.3
      target.instance_exec &block  
   end
end

class C
   private
   def hello
     puts "hello"
   end
end

p = Proxy.new
c = C.new
p.target = c
p.method { hello }

In this example the method call within the block { hello } has it true meaning in the context of the target object c.

This example is for illustrative purposes, only. Real working code that uses this kind of execute in the context of another object is not uncommon. The monitoring tool Godm for instance, uses it.