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POPython functions can be given new attributes from outside the scope?
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  1. POPython functions can be given new attributes from outside the scope?
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    copied!<p>I didn't know you could do this:</p> <pre><code>def tom(): print "tom's locals: ", locals() def dick(z): print "z.__name__ = ", z.__name__ z.guest = "Harry" print "z.guest = ", z.guest print "dick's locals: ", locals() tom() #&gt;&gt;&gt; tom's locals: {} #print tom.guest #AttributeError: 'function' object has no attribute 'guest' print "tom's dir:", dir(tom) # no 'guest' entry dick( tom) #&gt;&gt;&gt; z.__name__ = tom #&gt;&gt;&gt; z.guest = Harry #&gt;&gt;&gt; dick's locals: {'z': &lt;function tom at 0x02819F30&gt;} tom() #&gt;&gt;&gt; tom's locals: {} #print dick.guest #AttributeError: 'function' object has no attribute 'guest' print tom.guest #&gt;&gt;&gt; Harry print "tom's dir:", dir(tom) # 'guest' entry appears </code></pre> <p>Function tom() has no locals. Function dick() knows where tom() lives and puts up Harry as 'guest' over at tom()'s place. harry doesn't appear as a local at tom()'s place, but if you ask for tom's guest, harry answers. harry is a new attribute at tom().</p> <p>UPDATE: From outside tom(), you can say "print dir(tom)" and see the the tom-object's dictionary. (You can do it from <strong>inside</strong> tom(), too. So tom could find out he had a new lodger, harry, going under the name of 'guest'.)</p> <p>So, attributes can be added to a function's namespace from outside the function? Is that often done? Is it acceptable practice? Is it recommended in some situations? Is it actually vital at times? (Is it Pythonic?)</p> <p>UPDATE: Title now says 'attributes'; it used to say 'variables'. Here's a <a href="http://www.python.org/dev/peps/pep-0232/" rel="nofollow noreferrer">PEP about Function Attributes</a>.</p>
 

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