[Tutor] Const on Python

John Fouhy john at fouhy.net
Thu Mar 6 01:30:23 CET 2008

On 06/03/2008, Tiago Katcipis <katcipis at inf.ufsc.br> wrote:
>  learning. Im used to develop on c++ and java and i wanted to know if
>  there is any way to create a final or const member, a member that after
>  assigned cant be reassigned. Thanks to anyone who tries to help me and
>  sorry to bother with a so silly question. i hope someday i can be able
>  to help :-)

The short answer is: "Not really".

Actually, with recent versions of python, you could do something with
properties.  e.g.:

>>> class MyClass(object):
...     def fget_FOO(self):
...         return 'foo'
...     FOO = property(fget=fget_FOO)
>>> x = MyClass()
>>> x.FOO
>>> x.FOO = 'bar'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute

property() takes up to three arguments: get, set, and docstring.  In
this case, I omitted the setter.  Thus python doesn't allow me to set
that attribute.  You could also mess around with getattr() to achieve
a similar effect.

Generally, though, python takes the attitude that programmers are
adults capable of thinking for themselves, and if you're silly enough
to reassign a constant, you deserve whatever you get.  Best just to
make your variable names ALL_CAPS and write documentation saying
they're constant :-)

See also this recipe:
for another take on the issue.


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