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Python Ruby
objects and inheritance
class FooClass(BarClass): class FooClass < BarClass
class FooClass: class FooClass
isinstance(object, Class) or issubclass(type(object), Class) object.is_a? Class
type(object) == Class object.class == Class
multiple inheritance / mix-ins
class Foo(BaseClass, MixIn): class Foo < BaseClass
    include MixIn
public data (attributes) on classes = 'foo' attr_reader: foo, attr_accessor: foo or attr_writer: foo
private data (attributes/instance variables)
self.__foo = 'foo' @foo = 'foo' instance variables are private by default
print, str, repr
print("foo") print "foo"
print(repr("foo")) p "foo"
string slices
"foobar"[2:4] "foobar"[2...4] or "foobar"[2..3]
"foobar"[3:] "foobar"[3..-1]
"foobar"[:3] "foobar"[0...3] or "foobar"[0..2]
"foobar"[-1:0:-2] Ruby doesn't allow step in slice syntax
is a value in a collection?
value in collection collection.index(value)
0 < number < 100 0 < number and number < 100 or
(0+1...100) === number
function declaration and invocation
key-word arguments
def func(arg1, arg2, key3='val3', key4='val4'): Ruby does not have keyword arguments. key=value pairs in function definitions are positional arguments with default values.
arbitrary positional arguments
def func(arg1, arg2, *args): def func(arg1, arg2, *splat)
func(arg1, arg2, arg3, arg4) func(arg1, arg2, arg3, arg4)
default argument value interpretation: expression can be [], {}, "foo", etc
def func(arg=expression): def func(arg=expression)
expression is evaluated when the function is defined expression is reevaluated each time the function is called
run module as a script
if __name__ == '__main__': if __FILE__ == $0
exception handling
  raise FooException
except FooException:
  # handle FooException
  # do something if no errors
  # do something always
  raise FooException
rescue Exception => e
  # handle FooException
  # do something if no errors
 # do something always