第七章：Python基础のXML操作和面向对象(上集)

Posted 2020-08-08 代码艺术

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本課主題

XML介绍与操作实战
shutil 模块介绍与操作实战
subprocess 模块介绍与操作实战
初探面向对象与操作实战
本周作业

XML介绍和操作实战

對於浏览器返回的字符串有以下幾種：

html
JSON，表现是列表和字典的格式
XML

XML的應用

一个属性里包含多过属性，一类是页面上做展示的时候可以用到XML，就是为别人来调用（这也是字符串类型的一个XML格式数据）;另外一类是配置文件。你可以从文件里打开一个XML文件，它返回的是一个XML形式的字符串；也可以通过发送 HTTP请求，返回一个 XML 形式的字符串

XML函数功能

class Element:
    """An XML element.

    This class is the reference implementation of the Element interface.

    An element\'s length is its number of subelements.  That means if you
    want to check if an element is truly empty, you should check BOTH
    its length AND its text attribute.

    The element tag, attribute names, and attribute values can be either
    bytes or strings.

    *tag* is the element name.  *attrib* is an optional dictionary containing
    element attributes. *extra* are additional element attributes given as
    keyword arguments.

    Example form:
        <tag attrib>text<child/>...</tag>tail

    """

    当前节点的标签名
    tag = None
    """The element\'s name."""

    当前节点的属性

    attrib = None
    """Dictionary of the element\'s attributes."""

    当前节点的内容
    text = None
    """
    Text before first subelement. This is either a string or the value None.
    Note that if there is no text, this attribute may be either
    None or the empty string, depending on the parser.

    """

    tail = None
    """
    Text after this element\'s end tag, but before the next sibling element\'s
    start tag.  This is either a string or the value None.  Note that if there
    was no text, this attribute may be either None or an empty string,
    depending on the parser.

    """

    def __init__(self, tag, attrib={}, **extra):
        if not isinstance(attrib, dict):
            raise TypeError("attrib must be dict, not %s" % (
                attrib.__class__.__name__,))
        attrib = attrib.copy()
        attrib.update(extra)
        self.tag = tag
        self.attrib = attrib
        self._children = []

    def __repr__(self):
        return "<%s %r at %#x>" % (self.__class__.__name__, self.tag, id(self))

    def makeelement(self, tag, attrib):
        创建一个新节点
        """Create a new element with the same type.

        *tag* is a string containing the element name.
        *attrib* is a dictionary containing the element attributes.

        Do not call this method, use the SubElement factory function instead.

        """
        return self.__class__(tag, attrib)

    def copy(self):
        """Return copy of current element.

        This creates a shallow copy. Subelements will be shared with the
        original tree.

        """
        elem = self.makeelement(self.tag, self.attrib)
        elem.text = self.text
        elem.tail = self.tail
        elem[:] = self
        return elem

    def __len__(self):
        return len(self._children)

    def __bool__(self):
        warnings.warn(
            "The behavior of this method will change in future versions.  "
            "Use specific \'len(elem)\' or \'elem is not None\' test instead.",
            FutureWarning, stacklevel=2
            )
        return len(self._children) != 0 # emulate old behaviour, for now

    def __getitem__(self, index):
        return self._children[index]

    def __setitem__(self, index, element):
        # if isinstance(index, slice):
        #     for elt in element:
        #         assert iselement(elt)
        # else:
        #     assert iselement(element)
        self._children[index] = element

    def __delitem__(self, index):
        del self._children[index]

    def append(self, subelement):
        为当前节点追加一个子节点
        """Add *subelement* to the end of this element.

        The new element will appear in document order after the last existing
        subelement (or directly after the text, if it\'s the first subelement),
        but before the end tag for this element.

        """
        self._assert_is_element(subelement)
        self._children.append(subelement)

    def extend(self, elements):
        为当前节点扩展 n 个子节点
        """Append subelements from a sequence.

        *elements* is a sequence with zero or more elements.

        """
        for element in elements:
            self._assert_is_element(element)
        self._children.extend(elements)

    def insert(self, index, subelement):
        在当前节点的子节点中插入某个节点，即：为当前节点创建子节点，然后插入指定位置
        """Insert *subelement* at position *index*."""
        self._assert_is_element(subelement)
        self._children.insert(index, subelement)

    def _assert_is_element(self, e):
        # Need to refer to the actual Python implementation, not the
        # shadowing C implementation.
        if not isinstance(e, _Element_Py):
            raise TypeError(\'expected an Element, not %s\' % type(e).__name__)

    def remove(self, subelement):
        在当前节点在子节点中删除某个节点
        """Remove matching subelement.

        Unlike the find methods, this method compares elements based on
        identity, NOT ON tag value or contents.  To remove subelements by
        other means, the easiest way is to use a list comprehension to
        select what elements to keep, and then use slice assignment to update
        the parent element.

        ValueError is raised if a matching element could not be found.

        """
        # assert iselement(element)
        self._children.remove(subelement)

    def getchildren(self):
        获取所有的子节点（废弃）
        """(Deprecated) Return all subelements.

        Elements are returned in document order.

        """
        warnings.warn(
            "This method will be removed in future versions.  "
            "Use \'list(elem)\' or iteration over elem instead.",
            DeprecationWarning, stacklevel=2
            )
        return self._children

    def find(self, path, namespaces=None):
        获取第一个寻找到的子节点
        """Find first matching element by tag name or path.

        *path* is a string having either an element tag or an XPath,
        *namespaces* is an optional mapping from namespace prefix to full name.

        Return the first matching element, or None if no element was found.

        """
        return ElementPath.find(self, path, namespaces)

    def findtext(self, path, default=None, namespaces=None):
        获取第一个寻找到的子节点的内容
        """Find text for first matching element by tag name or path.

        *path* is a string having either an element tag or an XPath,
        *default* is the value to return if the element was not found,
        *namespaces* is an optional mapping from namespace prefix to full name.

        Return text content of first matching element, or default value if
        none was found.  Note that if an element is found having no text
        content, the empty string is returned.

        """
        return ElementPath.findtext(self, path, default, namespaces)

    def findall(self, path, namespaces=None):
        获取所有的子节点
        """Find all matching subelements by tag name or path.

        *path* is a string having either an element tag or an XPath,
        *namespaces* is an optional mapping from namespace prefix to full name.

        Returns list containing all matching elements in document order.

        """
        return ElementPath.findall(self, path, namespaces)

    def iterfind(self, path, namespaces=None):
        获取所有指定的节点，并创建一个迭代器（可以被for循环）
        """Find all matching subelements by tag name or path.

        *path* is a string having either an element tag or an XPath,
        *namespaces* is an optional mapping from namespace prefix to full name.

        Return an iterable yielding all matching elements in document order.

        """
        return ElementPath.iterfind(self, path, namespaces)

    def clear(self):
        清空节点
        """Reset element.

        This function removes all subelements, clears all attributes, and sets
        the text and tail attributes to None.

        """
        self.attrib.clear()
        self._children = []
        self.text = self.tail = None

    def get(self, key, default=None):
        获取当前节点的属性值
        """Get element attribute.

        Equivalent to attrib.get, but some implementations may handle this a
        bit more efficiently.  *key* is what attribute to look for, and
        *default* is what to return if the attribute was not found.

        Returns a string containing the attribute value, or the default if
        attribute was not found.

        """
        return self.attrib.get(key, default)

    def set(self, key, value):
        为当前节点设置属性值
        """Set element attribute.

        Equivalent to attrib[key] = value, but some implementations may handle
        this a bit more efficiently.  *key* is what attribute to set, and
        *value* is the attribute value to set it to.

        """
        self.attrib[key] = value

    def keys(self):
        获取当前节点的所有属性的 key

        """Get list of attribute names.

        Names are returned in an arbitrary order, just like an ordinary
        Python dict.  Equivalent to attrib.keys()

        """
        return self.attrib.keys()

    def items(self):
        获取当前节点的所有属性值，每个属性都是一个键值对
        """Get element attributes as a sequence.

        The attributes are returned in arbitrary order.  Equivalent to
        attrib.items().

        Return a list of (name, value) tuples.

        """
        return self.attrib.items()

    def iter(self, tag=None):
        在当前节点的子孙中根据节点名称寻找所有指定的节点，并返回一个迭代器（可以被for循环）。
        """Create tree iterator.

        The iterator loops over the element and all subelements in document
        order, returning all elements with a matching tag.

        If the tree structure is modified during iteration, new or removed
        elements may or may not be included.  To get a stable set, use the
        list() function on the iterator, and loop over the resulting list.

        *tag* is what tags to look for (default is to return all elements)

        Return an iterator containing all the matching elements.

        """
        if tag == "*":
            tag = None
        if tag is None or self.tag == tag:
            yield self
        for e in self._children:
            yield from e.iter(tag)

    # compatibility
    def getiterator(self, tag=None):
        # Change for a DeprecationWarning in 1.4
        warnings.warn(
            "This method will be removed in future versions.  "
            "Use \'elem.iter()\' or \'list(elem.iter())\' instead.",
            PendingDeprecationWarning, stacklevel=2
        )
        return list(self.iter(tag))

    def itertext(self):
        在当前节点的子孙中根据节点名称寻找所有指定的节点的内容，并返回一个迭代器（可以被for循环）。
        """Create text iterator.

        The iterator loops over the element and all subelements in document
        order, returning all inner text.

        """
        tag = self.tag
        if not isinstance(tag, str) and tag is not None:
            return
        if self.text:
            yield self.text
        for e in self:
            yield from e.itertext()
            if e.tail:
                yield e.tail

节点功能一览表

节点功能一览表

每一个节点都是一个 element 对象，节点里可以嵌套节点；这里的 book.xml 例子有 <书>：每本书分別都有<书名>，<作者>，<出版年份> 和 <价格> 4个属性。

<bookstore>
  <book category="cooking">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>
  <book category="children">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book category="web">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
  </book>
</bookstore>

Book.xml

把整个XML文件的树先取出来放在一个XML对象里，加载到内存里，它返回的是一个ElementTree 里的 ElementTree类型<class \'xml.etree.ElementTree.ElementTree\'>
```
>>> from xml.etree import ElementTree as ET
>>> xmltree = ET.parse(\'book.xml\')
>>> print(type(xmltree))
<class \'xml.etree.ElementTree.ElementTree\'>
```
ET.parse()

如果你想取它的根目录的话，调用getroot( )函数，它返回的是一个ElementTree 里的 Element类型 <class \'xml.etree.ElementTree.Element\'> 。

>>> xmltree = ET.parse(\'book.xml\')
>>> root = xmltree.getroot()
>>> print(root)
<Element \'bookstore\' at 0x10d065868>

>>> print(type(root))
<class \'xml.etree.ElementTree.Element\'>

getroot()例子

用的 open( )函数打开一个XML文件，它返回的是XML形式的字符串，然后通过调用XML( )函数来读取/操作出XML格式的文件，它返回的也是一个 ElementTree 里的Element类型<class \'xml.etree.ElementTree.Element\'> 。

>>> str_xmltree = open(\'book.xml\',\'r\').read() # 返回XML形式的字符串
>>> print(type(str_xmltree))
<class \'str\'>

>>> root = ET.XML(str_xmltree)
>>> print(root)
<Element \'bookstore\' at 0x10d06eb88>

>>> print(type(root)) 
<class \'xml.etree.ElementTree.Element\'>

ET.XML()例子

取出XML文件的 tag element，一個XML文件可以有很多 tag，tag 是構成XML格式的重要元素。比如在上面 bookstore 的例子里，tag 分別是 <bookstore>、<book>、<title>、<author>、<year>、<price>，如果想找到一個 XML 的 Tag，就可以調用 tag变量來找。

>>> xmltree = ET.parse(\'book.xml\')
>>> root = xmltree.getroot()
>>> print(root.tag) # 调用 tag 函数
bookstore

>>> for child in root: #下一层也有下一层的Tag
...     print(child.tag)
... 
book
book
book

>>> for child in root: #下一层也有下一层的Tag
...     print(child.tag)
...     for grandchild in child:
...         print(child.tag, grandchild.tag)
... 
book
book title
book author
book year
book price
book
book title
book author
book year
book price
book
book title
book author
book year
book price

tag变量

取出XML文件Tag中的metadata/attribue，例如: <book category="cooking">，catergory = "cooking" 就是調用以下函数可以拿到的，返回的是一个字典类型。

>>> xmltree = ET.parse(\'book.xml\')
>>> root = xmltree.getroot()
>>> for child in root:
...     print(child.tag, child.attrib,type(child.attrib))
... 
book {\'category\': \'cooking\'} <class \'dict\'>
book {\'category\': \'children\'} <class \'dict\'>
book {\'category\': \'web\'} <class \'dict\'>

attrib变量

想取出 Tag 裡值的話，例如: <author>Giada De Laurentiis</author>，可以調用 text变量

>>> xmltree = ET.parse(\'book.xml\')
>>> root = xmltree.getroot()
>>> for child in root:
...     for grandchild in child:
...         print(child.tag+"-"+grandchild.tag+":", grandchild.text)
... 

book-title: Everyday Italian
book-author: Giada De Laurentiis
book-year: 2005
book-price: 30.00
book-title: Harry Potter
book-author: J K. Rowling
book-year: 2005
book-price: 29.99
book-title: Learning XML
book-author: Erik T. Ray
book-year: 2003
book-price: 39.95

text变量

如何生成新的XML文件
如何创建节点
如何创建XML

<data title="\'CTO" age="50">
    <country name="Liechtenstein">
        <rank updated="yes">2</rank>
        <year>2023</year>
        <gdppc>141100</gdppc>
        <neighbor direction="E" name="Austria" />
        <neighbor direction="W" name="Switzerland" />
    </country>
    <country name="Singapore">
        <rank updated="yes">5</rank>
        <year>2026</year>
        <gdppc>59900</gdppc>
        <neighbor direction="N" name="Malaysia" />
    </country>
    <country name="Panama">
        <rank updated="yes">69</rank>
        <year>2026</year>
        <gdppc>13600</gdppc>
        <neighbor direction="W" name="Costa Rica" />
        <neighbor direction="E" name="Colombia" />
    </country>
</data>

xo.xml

>>> from xml.etree import ElementTree as ET
>>> tree = ET.parse(\'xo.xml\')
>>> root = tree.getroot()
>>> for child in root:
...     print(child.tag,child.attrib)
...     for grandchild in child:
...         print(grandchild.tag,grandchild.text)
... 

country {\'name\': \'Liechtenstein\'}
rank 2
year 2023
gdppc 141100
neighbor None
neighbor None
country {\'name\': \'Singapore\'}
rank 5
year 2026
gdppc 59900
neighbor None
country {\'name\': \'Panama\'}
rank 69
year 2026
gdppc 13600
neighbor None
neighbor None

XML例子

shutil 模块介绍和操作实战

这个模块主要是为了处理文件、文件夹和压缩文件，它文件內容，權限，文件夾嵌套文件夾、壓縮文件的處理。

文件操作：打开文件以及读写文件

拷贝文件：從一個文件拷贝到另外一個文件，这里接受的是一个文件对象 <class \'_io.TextIOWrapper\'>

import shutil

# Copy a file from source to destination
src = open("src.txt","r") #<class \'_io.TextIOWrapper\'>
dest = open("dest.txt","w") #<class \'_io.TextIOWrapper\'>

shutil.copyfileobj(src,dest)

拷贝文件(方法一)

拷贝文件：從一個文件拷贝到另外一個文件，这里接受的是一个文件字符串
```
import shutil

# Copy a file from source to destination
shutil.copyfile("f1.log","f2.log")
```
拷贝文件(方法二)

只拷贝文件的权限

import shutil

shutil.copymode("f1.log","第十七章：Python の Web开发基础 MVC与Django
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