On 10/12/11 07:41, sunil tech wrote:
/def app(x):/
/ return x.append(100)/
/
/p = app(a)/
/
/now list holds appended value [1,2,3,100]/
/but p is empty... why it is?/
Because app() returns the result of append().
But append() returns None, since it modifies the list in place.
This is one of the few features of Python I dislike. It would not have
been difficult to make these modifier methods return the thing modified.
This style would then allow chained methods.
We do it with strings:
"foobar is a string".rstrip('ing').upper()
because strings are immutable. But we could have done it with other
sequence types too. Sadly we didn't and history/tradition leaves us with
these counterintuitive modifiers that return None. It catches everybody
out at some point...
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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