[Vampire-public] Default variables in Python

[Nicolas Burrus]

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I've discovered a weird problem with default arguments which are mutable 
(lists, dictionaries).

One should not write:

def foo(arg1 = []):
    self.arg1 = arg1
    # ...

because arg1 default value will be shared.  That is, if foo modifies it, the 
next time foo will be called, the default argument will not be an empty list.

Instead, I use the following code:

def foo(arg1 = None):
    self.arg1 = arg1 or {}

The problem is explained here: http://www.python.org/doc/faq/general.html#id51

I've removed problematic code in Vampire, it should come in next commits.
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