Comments on: Python if/else in lambda

By: KingRadical

KingRadical — Wed, 04 Nov 2009 23:45:49 +0000

>>> print (lambda x: np.array([3, 4]) if x == 2 else 1)(2)
[3 4]

By: KingRadical

KingRadical — Wed, 04 Nov 2009 23:44:42 +0000

>>> print (lambda x: 0 if x == 2 else 1)(2)
0
>>> print (lambda x: 0 if x == 2 else 1)(3)
1

By: Guest

Guest — Wed, 10 Jun 2009 08:24:29 +0000

(lambda x: x!=2 and 1 or 0)

By: MA Nussli

MA Nussli — Mon, 11 Aug 2008 12:21:41 +0000

The “And”/”Or” solution doesn’t work in any case. At least, I didn’t manage to make it work.

For example, if your “True statement” is actually a value which is evaluated to a “False” expression(like 0, None, ” or []) then “False statement” will always be returned.
example:
print (lambda x:x==2 and 0 or 1)(2) —> 1
print (lambda x:x==2 and 0 or 1)(3) —> 1

Even worst, if one of the “True/False statements” cannot be evaluated to a boolean expression(like a numpy.array) then it won’t work at all…
example:
print (lambda x:x==2 and numpy.array([3,4]) or 1)(2)

Any idea to circumvent such problems??

By: Adway

Adway — Mon, 12 May 2008 08:55:39 +0000

I personally liked the ‘and’ ‘or’ idea. What’s wrong about it?

By: Jo

Jo — Sat, 23 Feb 2008 20:24:28 +0000

so after reading this it also means u could just do

condition and “True statement” or “Falsestatement”
which seams the easyest solution

By: Adriaan

Adriaan — Thu, 21 Feb 2008 23:10:35 +0000

Looks like there’s no real solid solution short of a helper function – like Marius said, ( and or ) fails if evaluates to False (the inverse, or and , is even worse), and Thomas’ [, ][not ]) will always evaluate both and , which can be problematic…

I’m starting to long for the ?: of c

By: Marius Gedminas

Marius Gedminas — Sun, 17 Feb 2008 17:46:35 +0000

Be very very careful about this X and Y or Z trick. It fails miserably when bool(Y) is False.

By: Nicolas

Nicolas — Sat, 16 Feb 2008 23:34:59 +0000

00:55 jamesh: isnt __new__ executed on every instanciation?
00:55 @ ikke: yes, but you had a __new__ on the metaclass
00:55 @ ikke: which is executed when you created a new class

Obviously :-/ Thanks James!

By: Nicolas

Nicolas — Sat, 16 Feb 2008 23:32:19 +0000

James: I thought the metaclass’ __new__ method is called on every instanciation?