Conditional operator in Python?

[thp at cs.ucr.edu]

Donn Cave <donn at u.washington.edu> wrote:
: Quoth thp at cs.ucr.edu:
: ...
: | Okay, factorial is a somewhat simplistic example.  Consider the
: | following function, which counts the k-way partitions of n:
: |
: |   p = lambda k, n : (
: |       ( k < 1  or k > n  ) and [0] or 
: |       ( n == 1 or n == k ) and [1] or 
: |       [p(k-1,n-1)+p(k,n-k)] 
: |     )[0]
: |
: | Using, say, ?: notation this would be written:
: |
: |   p = lambda k, n : 
: |     k < 1  or k > n  ? 0 :
: |     n == 1 or n == k ? 1 :
: |     p( k-1, n-1 ) + p (k, n-k )
: |
: | which seems much more concise and readable.

: I am working intermittently on a modification to some code that was
: written in C by someone with a compulsion for syntax like that.
: I spent many hours on a trivial rewrite of a module of his like
: the one I want to write, just so I could read it.

So: 
  - Put "if" before each condition.
  - Replace ":" by "else".
  - Replace "?" by ": return".

: Though the second example may be more concise and readable than
: the first, it's much less readable than a normal procedural solution.

I don't see why, say

   if by_land():
     lantern_count = 1
   elif by_sea():
     lantern_count = 2
   else: 
     lantern_count = 0

should be more readable than, say

   lantern_count = 
     if    by_land() :  1 
     elif  by_sea()  :  2 
     else            :  0

or simply

   lantern_count = if by_land(): 1 elif by_sea(): 2 else: 0

: The first on the other hand has the advantage that only the most
: obtuse author could argue that it's readable at all, while the
: second sort of legitimizes this kind of obfuscation in Python.

Lambda abstraction is a powerful feature that needs to be supported
with a selection operator.  The ?: notation is not the only option
for such a ternary operator.

Tom Payne