该文档说我可以：

lxml可以从本地文件，HTTP URL或FTP URL进行解析。它还会自动检测并读取gzip压缩的XML文件（.gz）。

（来自http://lxml.de/parsing.html “解析器”下）

但是快速实验似乎暗示了其他方面：

Python 3.4.1 (v3.4.1:c0e311e010fc, May 18 2014, 10:45:13) [MSC v.1600 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from lxml import etree
>>> parser = etree.HTMLParser()
>>> from urllib.request import urlopen
>>> with urlopen('https://pypi.python.org/simple') as f:
...   tree = etree.parse(f, parser)
...
>>> tree2 = etree.parse('https://pypi.python.org/simple', parser)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "lxml.etree.pyx", line 3299, in lxml.etree.parse (src\lxml\lxml.etree.c:72655)
  File "parser.pxi", line 1791, in lxml.etree._parseDocument (src\lxml\lxml.etree.c:106263)
  File "parser.pxi", line 1817, in lxml.etree._parseDocumentFromURL (src\lxml\lxml.etree.c:106564)
  File "parser.pxi", line 1721, in lxml.etree._parseDocFromFile (src\lxml\lxml.etree.c:105561)
  File "parser.pxi", line 1122, in lxml.etree._BaseParser._parseDocFromFile (src\lxml\lxml.etree.c:100456)
  File "parser.pxi", line 580, in lxml.etree._ParserContext._handleParseResultDoc (src\lxml\lxml.etree.c:94543)
  File "parser.pxi", line 690, in lxml.etree._handleParseResult (src\lxml\lxml.etree.c:96003)
  File "parser.pxi", line 618, in lxml.etree._raiseParseError (src\lxml\lxml.etree.c:95015)
OSError: Error reading file 'https://pypi.python.org/simple': failed to load external entity "https://pypi.python.org/simple"
>>>

我可以使用urlopen方法，但是文档似乎暗示通过URL更好。另外，如果文档不准确，尤其是当我开始需要做更复杂的事情时，我会担心依赖lxml。

从已知URL用lxml解析HTML的正确方法是什么？我应该在哪里查看该文件？

更新 ：如果我使用httpURL而不是一个URL，则会出现相同的错误https。