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POPython - Cleanest way to override __init__ where an optional kwarg must be used after the super() call?
 

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  1. POPython - Cleanest way to override __init__ where an optional kwarg must be used after the super() call?
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    <p>I love how beautiful python looks/feels and I'm hoping this can be cleaner (readability is awesome).</p> <p>What's a clean way to accept an optional keyword argument when overriding a subclassed <strong>init</strong> where the optional <code>kwarg</code> has to be used <strong>after</strong> the <code>super()</code> call? </p> <p>I have a django form where I'd like to accept an optional user argument, but if I define it as one of the arguments <code>user=None</code>, then the usual form call <code>form({})</code> assumes the positional argument refers to the keyword argument <code>user</code>.</p> <p>Code speaks better than (my) words:</p> <pre><code>def __init__(self, *args, **kwargs): user = None if 'user' in kwargs: user = kwargs.pop('user') super(BaseCheckoutForm, self).__init__(*args, **kwargs) if user: self.prefill_from_user(user) </code></pre> <p>I can make this the cleanest by looking into the actual <code>Form</code> class to see what arguments it's looking for, but one of the greatest things about subclassing anything in python is collecting all <code>args</code> and <code>kwargs</code> and passing it into whatever you subclassed. Also this doesn't hold up to any changes in the source.</p> <pre><code>def __init__(self, querydict=None, user=None): super(BaseCheckoutForm, self).__init__(querydict) if user: self.prefill_from_user(user) </code></pre> <p>But unfortunately I have:</p> <pre><code> def __init__(self, *args, **kwargs): # cannot define user=None as an argument because normal usage # of class expects a certain order of positional args user = None if 'user' in kwargs: # must pop now since super()__init__ isn't expecting a user kwarg user = kwargs.pop('user') super(BaseCheckoutForm, self).__init__(*args, **kwargs) if user: self.prefill_from_user(user) </code></pre> <p>Thanks for any input!</p>
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    1. USYuji 'Tomita' Tomita
    1. USYuji 'Tomita' Tomita
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    1. COOne tip: Check for `None` via `x is not None`. `not x` is `True` for several possibly valid values (like empty collections (including strings), zero(-equivalent numbers), obviously `False`, etc.). It's also more explicit/readable, some would say ;)
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    2. COI think it's more readable with just `if user:` and the other values would not be valid anyways (False, '', []). Would it be OK in my case then?
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      1. USYuji 'Tomita' Tomita
    3. COAs long as you're okay with any value passed in as `user` that doesn't equate to a logical `True` being ignored, then yes, it's fine. However, in many cases you can be burned by this. Just be aware of the differences!
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      1. USJoe Kington
 

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