Why aren't colons optional?

[Edward K. Ream]

Hi all,

Why are colons required after def, elif, else, except, finally, for, if,
try and while?  One would think the colon would be optional when the
colon is followed by a newline.

Obviously, colons are required in:

  if a == 1 : b = c
  elif a == 2 : b = d
  else : b = e

My question is: why isn't the following valid?

  if a == 1
  	b = c
  elif a == 2
  	b = d
  else
  	b = e
  	
Can anyone provide an example of similar code that Python can't parse
without colons?  My apologies if this is a perennial question.
  
Edward
--------------------------------------------------------------------
Edward K. Ream   email:  edream at tds.net
Leo: Literate Editor with Outlines
Leo: http://personalpages.tds.net/~edream/front.html
--------------------------------------------------------------------