Python 之lxml庫學習筆記三

最後更新：2018-12-05 來源：互聯網

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序列化：

序列化通常使用tostring()方法來返回一個字串，或者ElementTree.write()方法來寫入一個檔案，一個類檔案的對象，或者一個URL（通過FTP的PUT或者HTTP的POST）。二者都使用相同的關鍵字參數比如pretty_print來格式化輸出或者encoding來選擇一個特定的輸出編碼而不是簡單的ASCII。

>>> root =
etree.XML("<root><a></a></root>")
>>>
etree.tostring(root)

’<root><a></a></root>’

>>> print etree.tostring(root, xml_declaration=True)
<?xml
version=’1.0’ encoding=’ASCII’?>

<root><a></a></root>

>>> print etree.tostring(root, encoding="iso-8859-1")
<?xml
version=’1.0’ encoding=’iso-8859-1’?>

<root><a></a></root>

>>> print etree.tostring(root, pretty_print=True)
<root>

<a>

</a>
</root>

Note that pretty printing appends a newline at the end.

注意pretty列印在末尾添加一個新行。

從lxml2.0起，serialisation可以做的不止XML序列化，可以序列化到HTML或者通過傳遞函數關鍵字來提取常值內容。

>>> root =
etree.XML("<html><head/><body>Hello World</body></html>")

>>> etree.tostring(root) # default: method = ’xml’

’<html><head/><body>Hello World</body></html>’

>>> etree.tostring(root, method="xml") # same as above

’<html><head/><body>Hello World</body></html>’

>>> etree.tostring(root, method="html")

’<html><head></head><body>Hello World</body></html>’

>>> print etree.tostring(root, method="html", pretty_print=True)

<html>
<head></head>

<body>Hello World</body>

</html>

>>> etree.tostring(root, method="text")
b’HelloWorld’

對XML序列化而言，預設的文本編碼是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類：

一個ElementTree主要是圍繞在一個有根節點的樹的文檔封裝類。它提供了很多方法來解析，序列化以及一般的文檔處理。一個最大的區別是它作為一個整體文檔來序列化。與之相對的是序列化成單個的元素。

>>> 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>

從字串和檔案中解析：

fromstring()是解析字串最容易的方法

>>> 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()方法類似，但它主要用來把XML文字寫入源檔案。
>>> root =
etree.XML("<root>data</root>")
>>> print
root.tag
root
>>>
etree.tostring(root)
’<root>data</root>’

parse()方法用來從檔案或者類檔案對象中解析
>>> some_file_like =
StringIO.StringIO("<root>data</root>")
>>> tree =
etree.parse(some_file_like)
>>>
etree.tostring(tree)
’<root>data</root>’

注意parse()返回的是一個ElementTree對象，而不是字串解析方法的Element對象。

>>> root = tree.getroot()
>>> print
root.tag
root
>>>
etree.tostring(root)
’<root>data</root>’

本文章原先以中文撰寫並發佈於 aliyun.com，亦設英文版本，僅作資訊用途。本網站不對文章的準確性，完整性或可靠性或其任何翻譯作出任何明示或暗示的陳述或保證。如對該文章有任何疑慮或投訴，請傳送電郵至 info-contact@alibabacloud.com 並提供相關疑慮或投訴的詳細說明。職員會於 5 個工作天內與您聯絡，一經驗證之後，即會刪除該侵權內容。

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