Hi,
Alan said:
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...
Is that the same problem with using the len function on sequences and open on
files, or is it different?
Thanks.
Jim
-----Original Message-----
From: tutor-bounces+james.homme=highmark....@python.org
[mailto:tutor-bounces+james.homme=highmark....@python.org] On Behalf Of Alan
Gauld
Sent: Saturday, December 10, 2011 4:16 AM
To: tutor@python.org
Subject: Re: [Tutor] Need Explanation...
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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