[Tutor] checking for a condition across a list
Tim Peters
tutor@python.org
Mon, 14 May 2001 02:25:27 -0400
[Pijus Virketis]
> Thanks so much! Just one small note: the way you've written the
> function, the usage should be:
> >>> alltrue([1,1,1,1], isone) <-- inputs the other way around...
Wish I could say I was testing you, but, na, I screwed up -- cut 'n paste
error. Good eye!
> Oh, and one more thing. I've never before encountered the
> "return x ==1" statement before. What exactly does it do?
Hmm.
return expression
returns the value of expression from a function, where "expression" is any
expression. "x == y" is a specific expression that yields 1 if x == y, else
0. All the comparison operators work that way:
>>> 2 == 3
0
>>> 2 == 2
1
>>> 2 < 3
1
>>> 2 > 3
0
>>> 2 <= 3
1
>>> 2 >= 3
0
>>> 2 is 3
0
>>> 2 is not 3
1
>>> 'a' in 'abc'
1
>>> 'a' not in 'abc'
0
>>>
So
return x == 1
returns 1 as the value of the function if x equals 1, and returns 0 as the
value of the function if x does not equal 1. Clear? Clear!