序列化：
序列化通常使用tostring()方法来返回一个字符串，或者ElementTree.write()方法来写入一个文件，一个类文件的对象，或者一个URL（通过FTP的PUT或者HTTP的POST）。二者都使用相同的关键字参数比如pretty_print来格式化输出或者encoding来选择一个特定的输出编码而不是简单的ASCII。
>>> root =
etree.XML("<root><a><b/></a></root>")
>>>
etree.tostring(root)
’<root><a><b/></a></root>’
>>> print etree.tostring(root, xml_declaration=True)
<?xml
version=’1.0’ encoding=’ASCII’?>
<root><a><b/></a></root>
>>> print etree.tostring(root, encoding="iso-8859-1")
<?xml
version=’1.0’ encoding=’iso-8859-1’?>
<root><a><b/></a></root>
>>> print etree.tostring(root, pretty_print=True)
<root>
<a>
<b/>
</a>
</root>
Note that pretty printing appends a newline at the end.
注意pretty打印在末尾添加一个新行。
从lxml2.0起，serialisation可以做的不止XML序列化，可以序列化到HTML或者通过传递函数关键字来提取文本内容。
>>> root =
etree.XML("<html><head/><body><p>Hello<br/>World</p></body></html>")
>>> etree.tostring(root) # default: method = ’xml’
’<html><head/><body><p>Hello<br/>World</p></body></html>’
>>> etree.tostring(root, method="xml") # same as above
’<html><head/><body><p>Hello<br/>World</p></body></html>’
>>> etree.tostring(root, method="html")
’<html><head></head><body><p>Hello<br>World</p></body></html>’
>>> print etree.tostring(root, method="html", pretty_print=True)
<html>
<head></head>
<body><p>Hello<br>World</p></body>
</html>
>>> etree.tostring(root, method="text")
b’HelloWorld’
对XML序列化而言，默认的文本编码是ASCII
>>> br = root.find(".//br")
>>> br.tail = u"W\xf6rld"
>>> etree.tostring(root, method="text") # doctest: +ELLIPSIS
Traceback (most recent call last):
...
UnicodeEncodeError: ’ascii’
codec can’t encode character u’\xf6’ ...
>>>etree.tostring(root,
method="text", encoding="UTF-8")
b’HelloW\xc3\xb6rld’
>>> etree.tostring(root, encoding=unicode, method="text")
u’HelloW\xf6rld’
ElementTree类：
一个ElementTree主要是围绕在一个有根节点的树的文档包装类。它提供了很多方法来解析，序列化以及一般的文档处理。一个最大的区别是它作为一个整体文档来序列化。与之相对的是序列化成单个的元素。
>>> tree = etree.parse(StringIO("""\
<?xml
version="1.0"?>
<!DOCTYPE root SYSTEM "test" [ <!ENTITY tasty
"eggs"> ]>
<root>
<a>&tasty;</a>
</root>
"""))
>>> print(tree.docinfo.doctype)
<!DOCTYPE root SYSTEM "test">
>>> # lxml 1.3.4 and later
>>>
print(etree.tostring(tree))
<!DOCTYPE root SYSTEM "test" [
<!ENTITY tasty "eggs">
]>
<root>
<a>eggs</a>
</root>
>>> # lxml 1.3.4 and later
>>>
print(etree.tostring(etree.ElementTree(tree.getroot())))
<!DOCTYPE root
SYSTEM "test" [
<!ENTITY tasty "eggs">
]>
<root>
<a>eggs</a>
</root>
>>> # ElementTree and lxml <= 1.3.3
>>>
print(etree.tostring(tree.getroot()))
<root>
<a>eggs</a>
</root>
从字符串和文件中解析：
fromstring()是解析字符串最容易的方法
>>> some_xml_data = "<root>data</root>"
>>>
root = etree.fromstring(some_xml_data)
>>> print
root.tag
root
>>>
etree.tostring(root)
’<root>data</root>’
XML()方法和fromstring()方法类似，但它主要用来把XML文字写入源文件。
>>> root =
etree.XML("<root>data</root>")
>>> print
root.tag
root
>>>
etree.tostring(root)
’<root>data</root>’
parse()方法用来从文件或者类文件对象中解析
>>> some_file_like =
StringIO.StringIO("<root>data</root>")
>>> tree =
etree.parse(some_file_like)
>>>
etree.tostring(tree)
’<root>data</root>’
注意parse()返回的是一个ElementTree对象，而不是字符串解析方法的Element对象。
>>> root = tree.getroot()
>>> print
root.tag
root
>>>
etree.tostring(root)
’<root>data</root>’