Issue 4098: surprised by default list parameter

The attached file produced the following result:

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trott$ python2.5 p6.py
[]
[1234]
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I expected both times the empty list since the print
statement prints just a defaulted parameter ("e") which
was defaulted to an empty list literal ("[]") and never set
by supplying an actual class parameter.

The object property "entries" appears to be shared by
both instances. Why?

http://effbot.org/pyfaq/why-are-default-values-shared-between-objects.htm

The same recently cropped up on the users mailinglist under the topic
"default value in __init__".

OK. I've read the Python Reference Manual 7.6 "Function Definition".
It "explains" why this happens.

BUT: Why can`t the compiler make a copy of the default object, if
it's mutable (e.g. a list)? This can't be that difficult.

Yes, the default value expression could be evaluated each time the
function is called without the parameter. But it would be another language.
Default values are computed once, and this is a Python feature.

It can be useful, for example to cache computations, or to achieve
"early binding" in nested functions, as explained in the suggested FAQ.