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I've familiarized myself with the concept, most notably by watching Raymond Hettinger's excellent video and reading the accepted answer here and I am wondering what I got wrong.
class ReadHTML(object):
def __init__(self, url):
page = urlopen(url).read()
self.page = page
@classmethod
def from_file(cls, path):
page = open(path).read()
return cls(page)
This works
r = ReadHTML('http://example.com')
print r.page
and this is not
r = ReadHTML.from_file('example.html')
print r.page
it throws me an error, as if I was trying to "urlopen" a file:
File "/usr/lib/python2.7/urllib2.py", line 258, in get_type
raise ValueError, "unknown url type: %s" % self.__original
ValueError: unknown url type: <!doctype html>
Can you see what's wrong?
759
You are still calling the class initializer, ReadHTML.__init__(), when you call cls(page); that call is no different from calling ReadHTML(page), you are just using a different reference. This method only accepts a url parameter and the code passes that to urlopen() regardless.
Adjust your ReadHTML.__init__() method to handle being passed a page instead of a URL:
class ReadHTML(object):
def __init__(self, url=None, page=None):
if url is not None:
page = urlopen(url).read()
self.page = page
@classmethod
def from_file(cls, path):
page = open(path).read()
return cls(page=page)
Now the code supports both paths to produce an instance.
148
from_file opens the page, but so does your __init__() constructor, so if you do ReadHTML.from_file('example.html'), you are essentially doing:
page = urlopen(open('example.html').read()).read()
Personally, I prefer Martijn's solution, for semantic clarity, but here is an alternative:
class ReadHTML(object):
def __init__(self, url, opener=urlopen):
self.page = opener(url).read()
@classmethod
def from_file(cls, path):
return cls(path, opener=open)
This solution is advantageous because it gives you the capability of defining arbitrary openers (say, for opening files stored in a database).
38
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