To Ruby From Python

Python is another very nice general purpose programming language. Going from Python to Ruby, you’ll find that there’s a little bit more syntax to learn than with Python.

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. (Python 3+ doesn’t have this issue, but it isn’t fully backward compatible with Python 2.)
  • 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__.
  • “mixins” 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.
  • There’s no way to unset a variable once set (like Python’s del statement). You can reset a variable to nil, allowing the old contents to be garbage collected, but the variable will remain in the symbol table as long as it is in scope.