title: How Python's a, b = b, a works?
body: <p>i know that my will seem trivial,but i cant figure out why isn't 'stop' equal to zero, since 'start' value is already overwritten.But when i simulate the same scenario out of the function it does indeed overwrite it.Am i missing something here?</p>
  
  <pre><code>def interval(start, stop =None, step = 1 ):
      'Imitates range() for step &gt;0 '
      if stop is None:
          start, stop = 0, start #since start is already 0, why isn't stop as well?
          print start,stop , step
      result = []
      i = start
      while i&lt; stop:
          result.append(i)
          i+=step 
      return result
  </code></pre>