Question

In Ruby 1.9, I can use its class variable like the following:

class Sample
  @@count = 0

  def initialize
    @@count += 1
  end

  def count
    @@count
  end
end

sample = Sample.new
puts sample.count     # Output: 1

sample2 = Sample.new
puts sample2.count    # Output: 2

How can I achieve the above in Python 2.5+ ?

Answer 1

class Sample(object):
  _count = 0

  def __init__(self):
    Sample._count += 1

  @property
  def count(self):
    return Sample._count

The use is a bit different from Ruby; e.g. if you have this code in module a.py,

>>> import a
>>> x = a.Sample()
>>> print x.count
1
>>> y = a.Sample()
>>> print x.count
2

having a Sample.count “class property” (with the same name as the instance property) would be a bit tricky in Python (feasible, but not worth the bother IMHO).