Please excuse me if this is obvious to others, but I can't figure it
out. I am subclassing dict, but want to prevent direct changing of
some key/value pairs. For this I thought I should override the
__setitem__ method as such:
class xs(dict):
"""
XS is a container object to hold information about cross sections.
"""
def __new__(cls, xS=1.0, xF=1.0, xG=1.0, nu=1.0, debug=0):
"""
"""
x = {}
x['xS'] = xS
x['xF'] = xF
x['nu'] = nu
x['xG'] = xG
x['xA'] = x['xG'] + x['xF']
x['xT'] = x['xA'] + x['xS']
return x
def __setitem__(self, key, value):
"""
I have overridden this method to prevent setting xT or xA
outside the
class.
"""
print "I am in __setitem__"
if key == 'xT':
raise AttributeError("""Can't change xT. Please change,
xF, xS, or xG""")
But I can't even get __setitem__ to run. Example:
Python 2.5 (r25:51918, Sep 19 2006, 08:49:13)
[GCC 4.0.1 (Apple Computer, Inc. build 5341)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import xs
>>> cs = xs.xs()
>>> cs
{'xA': 2.0, 'xF': 1.0, 'xG': 1.0, 'xS': 1.0, 'nu': 1.0, 'xT': 3.0}
>>> cs['xT'] = 3.1415
>>> cs
{'xA': 2.0, 'xF': 1.0, 'xG': 1.0, 'xS': 1.0, 'nu': 1.0, 'xT':
3.1415000000000002}
Is this what the __setitem__ method is for? If not, how can I do what
I want to do?
Thanks in advance,
Jeremy
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