[C++-sig] Re: FW: Injected constructors

[Ralf W. Grosse-Kunstleve]

--- Nicodemus <nicodemus at globalite.com.br> wrote:
> On a side note, this is a good reason to use classmethods in Python:
> 
> class ConfigurationLoader(object):
>     '''loads configuration from a filename or a file-like object.
>     '''
> 
>     def __init__(self, file_object):
>          self.file = file_object
> 
>     def FromFileName(cls, filename):
>          self = cls(file(filename))
>          return self
> 
>     FromFileName = classmethod(FromFileName)
> 
> 
> # usage
> config = ConfigurationLoader.FromFileName('test')
> 
> 
> This avoids having to do type checking in the __init__ method, plus it 
> makes the code a little more readable. 8)

FWIW: here is my preferred solution:

  def __init__(self, file_object=None, file_name=None):
    assert file_object is None or file_name is None
    assert file_object is not None or file_name is not None

Ralf


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