"Dick Moores" <[EMAIL PROTECTED]> wrote
But why will a tuple with two elements will always evaluate to
True?
Thats the rule for evaluationg collections in Python.
An empty collection is False. Anything else is therefore true
Yes! A rule, not logic. I'm not contradicting Kent, just helping myself understand. First the rule, then logic in the application of the rule. And I assume the rule is there in Python because it makes things work better.
_Learning Python_ has an enlightening section, "The Meaning of True and False in Python", on p. 188 in the 3rd edition. I quote in part:
===================================
In Python, as in most programming languages, an integer 0 represents false, and an integer 1 represents true. In addition, though, Python recognizes any empty data structure as false, and any nonempty data structure as true. More generally, the notions of true and false are intrinsic properties of every object in Python -- each object is either true or false, as follows:
-- Numbers are true if nonzero.
-- Other objects are true if nonempty.
===================================
Martin Walsh introduced me to bool(). That was useful:
In [43]: bool([])
Out[43]: False
In [44]: bool([1,2])
Out[44]: True
In [45]: bool("")
Out[45]: False
In [46]: bool("foo")
Out[46]: True
In [48]: bool(())
Out[48]: False
In [49]: bool((0))
Out[49]: False
In [50]: bool((0,))
Out[50]: True
In [51]: bool([[]])
Out[51]: True
In [52]: bool("''")
Out[52]: True
In [53]: bool(None)
Out[53]: False
In [55]: bool(set())
Out[55]: False
In [56]: bool(set([]))
Out[56]: False
In [57]: bool([None])
Out[57]: True
In [58]: bool(0)
Out[58]: False
In [59]: bool(1)
Out[59]: True
In [60]: bool(87657865)
Out[60]: True
In [61]: bool(876.57865)
Out[61]: True
In [62]: bool(-876.57865)
Out[62]: True
And so it goes..
Dick
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