title: Why does (a,b)=(b,a) work when a=b+a; b=a doesn't?
body: <p>I've tried to generate the fibonacci in python but I've noticed that if I do it with swapping it gives me a different value than if I was to do it with simple assignment</p>
  
  <pre><code>def fib_num(max):
      a = 0
      b = 1
      for i in range(max):
           # a,b = b+a,a  this way it is right
  
           # but if I will implement it like below with simple assigment,
           # I am not going to get the same result Why???
           a  = b+a  
           b = a
  
           yield a
  </code></pre>