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copied!<p>"Explicit is better than implicit." You should just document that your users need to use <code>MyList()</code> instead of <code>list()</code>. You and your users will be happier in the long run.</p> <p>Ruby allows what you want, by the way. With Ruby, you can open up global objects and just add new behaviors. I find this scary, and Ruby runs slower than Python, so I'm not actually urging you to switch to Ruby.</p> <p>So, provide <code>MyList()</code>, and provide a way to take an existing list and wrap it in a <code>MyList()</code>.</p> <p>You could write <code>MyList()</code> to just take a bunch of arguments, and make a list very conveniently:</p> <pre><code>class MyList(object): def __init__(self, *args): self.lst = args # add other methods to MyList() here </code></pre> <p>then you could call this with <code>MyList(1, 2, 3, 4)</code> and the instance would have a member called lst with the value: <code>[1, 2, 3, 4]</code></p> <p>But now, if you want to make a <code>MyList</code> instance out of a list, how do you do that? If you do this:</p> <pre><code>new_list = [1, 3, 5] x = MyList(new_list) </code></pre> <p>then you have just set x to: <code>[[1, 3, 5]]</code></p> <p>So I recommend you make <code>MyList()</code> just take a list argument and save it:</p> <pre><code>def ensure_list(seq): try: seq[0] return seq except TypeError: return list(seq) class MyList(object): def __init__(self, seq): self.lst = ensure_list(seq) # add other methods to MyList() here </code></pre> <p>I just edited this answer. Originally, I had a call to <code>list()</code> where I now have put a call to <code>ensure_list()</code>. <code>ensure_list()</code> checks to see if you can index its argument; if you can, it is either a list already or something that can act like a list, and it is returned unchanged. If you can't index it, then <code>ensure_list()</code> calls <code>list(seq)</code> to try to turn it into a list. This will work with iterators and generators, forcing them to expand out to a list.</p>

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