Question

I have a container class for urls and their headers, Resource:

class Resource(object):
    def __init__(self, url, headers):
        self.url = url
        self.content-length = headers['content-length']
        self.content-type = headers['content-type']

        # etc....

The headers argument to the __init__ method expects a dict returned from the getinfo() method of urllib2.urlopen(). I thought this would be a more readable way of packaging up the resource url and headers. Typing self.someheader = headers['someheader'] over and over made me wonder if there’s some way to automate creating variables from dictionary keys like this. Is this possible?

Answer 1

Python identifiers can’t have the - symbol in them! So we can replace it with _ in the keys.
Changing the keys to lowercase makes them look like a conventional variable name, and, what is very important, removes uppercase/lowercase confusion (because headers are usually sent with capitalized keys).

for k, v in headers.items():
    setattr(self, k.lower().replace('-', '_'), v)

If you’re using Python 2, iteritems is better here, as it doesn’t create a new list of items, but just lets you iterate over them, which Python 3 does by default.

It may be a good idea to store those keys in a “private” dict (e. g. self._headers). Then you can have much more control over the process with __getattr__ and __setattr__, for example, an exception can be raised during an attempt to set an invalid key.