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Re: [Pulp-list] Default values in method signatures



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On 03/10/2011 02:08 PM, Jay Dobies wrote:
> 
> This came up today with respect to the Filter __init__ method. The issue
> surrounds the signature:  def __init__(self, id, type, description=None,
> package_list=[]):
> 
> I first learned this was an issue when PyCharm started highlighting them
> in our code base. From PyCharm's inspection description:
> 
> "Default argument values are evaluated only once at function definition
> time, which means that modifying the default value of the argument will
> affect all subsequent calls of the function. "
> 
> In other words, all Filter instances that don't pass in package_list
> will point to the same list object. If they start to dork with its
> contents, *all* Filter objects will reflect the package list.
> 
> A workaround could be:
> 
> def __init__(self, id, type, description=None, package_list=None):
>     if not package_list:
>         package_list = []
>     self.package_list = package_list
> 
> That way a new list is created on each instantiation if one is not
> passed in.
> 
> BTW, this is all over our code. I mentioned it back in August
> (https://www.redhat.com/archives/pulp-list/2010-August/msg00030.html) so
> please try to clean these up when you see them.

One quick note I forgot to mention, this applies to {} created in method
signatures as well.


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- -- 
Jay Dobies
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http://pulpproject.org
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