Not possible to hide local variables

Cecil Westerhof Cecil at
Wed Apr 29 08:16:01 CEST 2015

Op Tuesday 28 Apr 2015 09:56 CEST schreef Ethan Furman:

> On 04/28, Cecil Westerhof wrote:
>> If I remember correctly you can not hide variables of a class or
>> make them read-only?
>> I want to rewrite my moving average to python. The init is:
>> def __init__(self, length):
>> if type(length) != int:
>> raise ParameterError, 'Parameter has to be an int'
>> if n < 0:
>> raise ValueError, 'Parameter should be greater or equal 2'
>> self.length             = length
>> self.old_values         = []
>> self.current_total      = 0
>> But when someone changes length, old_values, or current_total that
>> would wreck havoc with my class instance. What is the best way to
>> handle this?
> Prefix those names with a single leading underscore, which is the
> convention for private variables.


> This way, if some user (maybe you! ;) has a good reason to change
> those values in can be done, but it is quite clear that said user is
> mucking about with internals and they are on their own.

There is something to say for this way of working.

Cecil Westerhof
Senior Software Engineer

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