title: Reduce function fails with three parameters and runs fine with two parameters in python
body: <pre><code>from functools import reduce
  o = [20,30,100,60,80,90]
  
  #1 
  print(reduce((lambda x,y:x+y),o)) # returns 380
  #2
  print(reduce((lambda x,y,z:x+y+z),o)) # FAILS
  #3
  print(reduce((lambda x,y,z=10:x+y+z),o)) # returns 430 
  </code></pre>
  <p>Can someone explain why the #1 is working fine and #2 fails.</p>