What does Ruby have that Python doesn t and vice versa

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There is a lot of discussions of Python vs Ruby  and I all find them completely unhelpful  because they all turn around why feature X sucks in language Y  or that claim language Y doesn t have X  although in fact it does  I also know exactly why I prefer Python  but that s also subjective  and wouldn t help anybody choosing  as they might not have the same tastes in development as I do   It would therefore be interesting to list the differences  objectively  So no  Python s lambdas sucks   Instead explain what Ruby s lambdas can do that Python s can t  No subjectivity  Example code is good   Don t have several differences in one answer  please  And vote up the ones you know are correct  and down those you know are incorrect  or are subjective   Also  differences in syntax is not interesting  We know Python does with indentation what Ruby does with brackets and ends  and that   is called self in Python   UPDATE  This is now a community wiki  so we can add the big differences here   Ruby has a class reference in the class body  In Ruby you have a reference to the class  self  already in the class body  In Python you don t have a reference to the class until after the class construction is finished   An example   class Kaka   puts self end   self in this case is the class  and this code would print out  Kaka   There is no way to print out the class name or in other ways access the class from the class definition body in Python  outside method definitions    All classes are mutable in Ruby  This lets you develop extensions to core classes   Here s an example of a rails extension   class String   def starts with  other      head   self 0  other length      head    other   end end   Python  imagine there were no    startswith method    def starts with s  prefix       return s  len prefix      prefix   You could use it on any sequence  not just strings   In order to use it you should import it explicitly e g   from some module import starts with   Ruby has Perl-like scripting features  Ruby has first class regexps   -variables  the awk perl line by line input loop and other features that make it more suited to writing small shell scripts that munge text files or act as glue code for other programs   Ruby has first class continuations  Thanks to the callcc statement  In Python you can create continuations by various techniques  but there is no support built in to the language   Ruby has blocks  With the  do  statement you can create a multi-line anonymous function in Ruby  which will be passed in as an argument into the method in front of do  and called from there  In Python you would instead do this either by passing a method or with generators   Ruby   amethod    here      many lines of code     goes here      Python  Ruby blocks correspond to different constructs in Python    with amethod   as here     amethod   is a context manager     many lines of code     goes here    Or  for here in amethod       amethod    is an iterable     many lines of code     goes here    Or  def function here       many lines of code     goes here   amethod function         function  is a callback   Interestingly  the convenience statement in Ruby for calling a block is called  yield   which in Python will create a generator   Ruby   def themethod     yield 5 end  themethod do  foo      puts foo end   Python   def themethod        yield 5  for foo in themethod        print foo   Although the principles are different  the result is strikingly similar   Ruby supports functional style  pipe-like  programming more easily  myList map  amp  description  reject  amp  empty   join   n     Python   descriptions    f description   for f in mylist    n  join filter len  descriptions     Python has built-in generators  which are used like Ruby blocks  as noted above   Python has support for generators in the language  In Ruby 1 8 you can use the generator module which uses continuations to create a generator from a block  Or  you could just use a block proc lambda  Moreover  in Ruby 1 9 Fibers are  and can be used as  generators  and the Enumerator class is a built-in generator 4  docs python org has this generator example   def reverse data       for index in range len data -1  -1  -1           yield data index    Contrast this with the above block examples   Python has flexible name space handling  In Ruby  when you import a file with require  all the things defined in that file will end up in your global namespace  This causes namespace pollution  The solution to that is Rubys modules  But if you create a namespace with a module  then you have to use that namespace to access the contained classes   In Python  the file is a module  and you can import its contained names with from themodule import    thereby polluting the namespace if you want  But you can also import just selected names with from themodule import aname  another or you can simply import themodule and then access the names with themodule aname  If you want more levels in your namespace you can have packages  which are directories with modules and an   init   py file   Python has docstrings  Docstrings are strings that are attached to modules  functions and methods and can be introspected at runtime  This helps for creating such things as the help command and automatic documentation   def frobnicate bar          frobnicate takes a bar and frobnicates it          gt  gt  gt  bar   Bar           gt  gt  gt  bar is frobnicated          False         gt  gt  gt  frobnicate bar          gt  gt  gt  bar is frobnicated          True           Ruby s equivalent are similar to javadocs  and located above the method instead of within it   They can be retrieved at runtime from the files by using 1 9 s Method source location example use  Python has multiple inheritance  Ruby does not   on purpose  -- see Ruby s website  see here how it s done in Ruby   It does reuse the module concept as a type of abstract classes   Python has list dict comprehensions  Python   res    x x for x in range 1  10     Ruby   res    0  9  map    x  x   x     Python    gt  gt  gt   x x for x in range 10    lt generator object  lt genexpr gt  at 0xb7c1ccd4 gt   gt  gt  gt  list     0  1  4  9  16  25  36  49  64  81    Ruby   p   proc    x  x   x    0  9  map  amp p    Python 2 7     gt  gt  gt   x str y y  for x y in  1 2  3 4  items     1   4   3   16     Ruby    gt  gt  Hash  1  gt 2  3  gt 4  map  x y   x  y y  to s      gt   1  gt  4   3  gt  16     Python has decorators  Things similar to decorators can also be created in Ruby  and it can also be argued that they aren t as necessary as in Python   Syntax differences  Ruby requires  end  or     to close all of its scopes  while Python uses white-space only   There have been recent attempts in Ruby to allow for whitespace only indentation http   github com michaeledgar seamless

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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

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python has named optional arguments  def func a  b 2  c 3       print a  b  c   gt  gt  gt  func 1  1 2 3  gt  gt  gt  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

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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

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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

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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

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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  lt  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  lt  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

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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

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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

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Ruby has builtin continuation support using callcc   Hence you can implement cool things like the amb-operator

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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

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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

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At this stage  Python still has better unicode support

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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    gt  gt  PI   3 14   gt  3 14  gt  gt  PI    1  irb  2  warning  already initialized constant PI   gt  4 14   Python    gt  gt  gt  PI   3 14  gt  gt  gt  PI    1  gt  gt  gt  PI 4 1400000000000006

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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

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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

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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

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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

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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  lt  lt  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

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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  amp block         Ruby 1 9 or in Rails 2 3       target instance exec  amp 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

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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    Split the sentence up into words Reverse the words 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

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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

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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

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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

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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           gt   Hello   def func2  print  Goodbye   self class send  define method   func  method  func2   func                         gt   Goodbye    method  func  owner          gt  Object func                         gt   Goodbye   self func                    gt   Goodbye

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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

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You can have code in the class definition in both Ruby and Python  However  in Ruby you have a reference to the class  self   In Python you don t have a reference to the class  as the class isn t defined yet   An example   class Kaka   puts self end   self in this case is the class  and this code would print out  Kaka   There is no way to print out the class name or in other ways access the class from the class definition body in Python

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The nested lexical scope example that someone gave gives several benefits     Safer  globals 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

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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    gt  gt  enum    1  4  to enum   gt    lt Enumerator 0x1344a8 gt    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     gt  gt  1  3  3 foo 1 c 5   gt  gt  1  5  3 c           gt  gt  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  gt 3   gt  gt  1  3  3 foo 1  c  gt 5   gt  gt  1  2  5   Reference  The Pragmatic Progammer s Guide to Ruby

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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

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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

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Ruby has embedded documentation     begin   You could use rdoc to generate man pages from this documentation    end

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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            Ruby s iterators and codeblocks vs Python s iterators    and generators    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

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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    gt   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

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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

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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

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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

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

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