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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 1. Working with xml 
Step1:  1.3 From file to XML object
Opening an xml file is actually quite simple 
Step2:  As you can see, we obtained an instance of type lxml.etree._ElementTree. It means the xml markup has been transformed into something Python understands.
The parse function of etree does not take many arguments. One way to customize its behaviour is to give it a home configured or homemade xml parser 
Step3:  From the documentation of the XMLParser function, here are some arguments that might be useful for you 
Step4:  DIY
Can you parse a xml document made of one tag "humanities" with two children "field" named "classics" and "history"?
Step6:  1.3.2 Errors and understanding them
Previouly, we have said that lxml was quite strict about xml validity. Let's see an example 
Step10:  What error did we raise trying to parse this XML ? We got an XMLSyntaxError. It can happen for various reasons, including when entities cannot be parsed. Can you try to find another way to raise an XMLSyntaxError ?
Step11:  As you can see, errors are detailed enough so you can correct your own XML, at least manually.
1.3.3 Node properties and methods
Quick explanation 
Step13:  You can do plenty of things using lxml and access properties or methods of nodes, here is an overview of reading functionalities offered by lxml 
Step14:  If we want to retrieve the attributes of our div, we can do as follow 
Step15:  Great ! We accessed our first information using lxml ! Now, how about getting somewhere other than the root tag ? To do so, there are two ways 
Step16:  Now that we have access to our children, we can have access to their text 
Step17:  Ok, we are now able to get some stuff done. Remember the namespace naming ? Sometimes it's useful to retrieve namespaces and their prefix 
Step19:  What you've learned 
Step20:  As you can see, the xpath returns a list. This behaviour is intended, since an xpath can retrieve more than one item 
Step21:  You see ? The xpath //l returns two elements, just like python does in a list. Now, let's apply some xpath to the children and see what happens 
Step22:  As you can see, you can do xpath from any node in lxml. One important thing though 
Step24:  Xpath with namespaces and prefix
As you've seen, lxml use Clark's naming convention for expressing namespaces. This is extremely important regarding xpath, because you will be able to retrieve a node using it under certain conditions 
Step27:  What you have learned 
Step28:  Did you see what happened ? We used xslt(xml). etree.XSLT() transforms a xsl document into a function, which then takes one parameter (in this case an xml document). But can you figure out what this returns ? Let's ask Python 
Step29:  The result is not of the same type of element we usually have, even though it does share most of its methods and attributes 
Step30:  And has something more 
Step33:  XSLT is more complex than just inputing xml. You can do XSLT using parameters as well. In this case, your parameters will be accessibles as a named argument to the generated function. If your XSL has a name xsl-param, the function given back by etree.XSLT will have a name argument 
Step34:  2. Using ElementTree
Step35:  2.1 Traversing the Parsed Tree
To visit all of the children in order, use iter() to create a generator that iterates over the ElementTree instance.
Step36:  2.1.1 Finding Nodes in a Document¶
Walking the entire tree like this searching for relevant nodes can be error prone. The example above had to look at each outline node to determine if it was a group (nodes with only a text attribute) or podcast (with both text and xmlUrl). To produce a simple list of the podcast feed URLs, without names or groups, for a podcast downloader application, the logic could be simplified using findall() to look for nodes with more descriptive search characteristics.
As a first pass at converting the above example, we can construct an XPath argument to look for all outline nodes.
Step37:  Another version can take advantage of the fact that the outline nodes are only nested two levels deep. Changing the search path to .//outline/outline mean the loop will process only the second level of outline nodes.
Step38:  2.1.2 Parsed Node Attributes
The items returned by findall() and iter() are Element objects, each representing a node in the XML parse tree. Each Element has attributes for accessing data pulled out of the XML. This can be illustrated with a somewhat more contrived example input file, data.xml
Step39:  2.1.3 Parsing Strings
To work with smaller bits of XML text, especially string literals as might be embedded in the source of a program, use XML() and the string containing the XML to be parsed as the only argument.
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Python Code:
from lxml import etree
Explanation: 1. Working with xml : reading
1.1 Introduction
Extensible Markup Language (XML) is a simple, very flexible text format derived from SGML (ISO 8879). Originally designed to meet the challenges of large-scale electronic publishing, XML is also playing an increasingly important role in the exchange of a wide variety of data on the Web and elsewhere.
It has been defined at https://www.w3.org/XML/. 
Several schema systems exist to aid in the definition of XML-based languages, while programmers have developed many application programming interfaces (APIs) to aid the processing of XML data.
1.2 Parsing XML with Python
As for querying the web, Python has many libraries for playing with xml. You will most likely encounter the following during your Pythonic journey :
lxml, which we will use for this course. A clean, quite fast, strict library for dealing with xml resources. It's the most accepted library for this kind of request. If IBM writes tutorials for it, it should be good. It supports xpath and xslt.
BeautifulSoup. Flexible, average speed. The good thing is if your xml markup is messed up, it will try to correct it. It's perfect for dealing with web scrapped data in HTML formats. For clean xml, it might be too slow.
xml : the native integration in Python. Fast, clean but no good sides such as xpath and xslt.
Read about others on the Python official wiki
Based on my experience, lxml will meet most of your needs when dealing with clean data. Clean is the key word here : do not expect lxml to play well with bad html or bad xml. It will just throw errors at you until you give up or fix it by hand.
We can import lxml.etree the same way we imported requests earlier.
End of explanation
# We open our file
with open("data/books.xml") as file:
    # We use the etree.parse property
    parsed = etree.parse(file)
# We print the object
print(parsed)
Explanation: 1.3 From file to XML object
Opening an xml file is actually quite simple : you open it and you parse it. Who would have guessed ?
End of explanation
# We initiate a new parser from etree, asking it to remove nodes of text which are empty
parser = etree.XMLParser(remove_blank_text=True)
# We open the file
with open("data/books.xml") as file:
    # And we parse using the new parser
    parsed = etree.parse(file, parser)
# We print the object
print(parsed)
# We open the file
Explanation: As you can see, we obtained an instance of type lxml.etree._ElementTree. It means the xml markup has been transformed into something Python understands.
The parse function of etree does not take many arguments. One way to customize its behaviour is to give it a home configured or homemade xml parser :
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xml = '<root xmlns:a="xmlns1" xmlns:b="xmlns2"><tag xmlns:c="xmlns3" /><tag xmlns:a="xmlns1" /><tag /></root>'
parsed = etree.fromstring(xml)
print(parsed)
Explanation: From the documentation of the XMLParser function, here are some arguments that might be useful for you :
attribute_defaults : Use DTD (if available) to add the default attributes
dtd_validation : Validate against DTD while parsing
load_dtd : Load and parse the DTD while parsing
ns_clean : Clean up redundant namespace declarations
recover : Try to fix ill-formed xml
remove_blank_text : Removes blank text nodes
resolve_entities : Replace entities by their value (Default : on)
You can then create a new parser according to its standards or clean namespace attribute. In this context, ns_clean would transform
&lt;root xmlns:a="xmlns1" xmlns:b="xmlns2"&gt;&lt;tag xmlns:c="xmlns3" /&gt;&lt;tag xmlns:a="xmlns1" /&gt;&lt;tag /&gt;&lt;/root&gt;
into
&lt;root xmlns:a="xmlns1" xmlns:b="xmlns2"&gt;&lt;tag xmlns:c="xmlns3" /&gt;&lt;tag/&gt;&lt;tag /&gt;&lt;/root&gt;
1.3.1 From string to XML object
lxml parses strings in the same way that it parses files. The syntax differs, but is quite simple :
End of explanation
# Put your code here
Explanation: DIY
Can you parse a xml document made of one tag "humanities" with two children "field" named "classics" and "history"?
End of explanation
xml = 
<fileDesc>
    <titleStmt>
        <title>Aeneid</title>
        <title type="sub">Machine readable text</title>
        <author n="Verg.">P. Vergilius Maro</author>
        <editor role="editor" n="Greenough">J. B. Greenough</editor>
    </titleStmt>
    <extent>about 505Kb</extent>
    <!-- &Perseus.publish;-->
    <sourceDesc>
        <biblStruct>
            <monogr>
                <author>Vergil</author>
                <title>Bucolics, Aeneid, and Georgics Of Vergil</title>
                <editor role="editor">J. B. Greenough</editor>
                <imprint>
                    <pubPlace>Boston</pubPlace>
                    <publisher>Ginn &amp; Co.</publisher>
                    <date>1900</date>
                </imprint>
            </monogr>
        </biblStruct>
    </sourceDesc>
</fileDesc>
etree.fromstring(xml)
Explanation: 1.3.2 Errors and understanding them
Previouly, we have said that lxml was quite strict about xml validity. Let's see an example :
End of explanation
#Write your xml in xml variable
# invalid
xml = 
# 
xml2 = 
<start>this is a text</start>
#
xml3 = 
<start attr="test"/>
etree.fromstring(xml3)
Explanation: What error did we raise trying to parse this XML ? We got an XMLSyntaxError. It can happen for various reasons, including when entities cannot be parsed. Can you try to find another way to raise an XMLSyntaxError ?
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# With no namespace
print(etree.fromstring("<root />"))
# With namespace
print(etree.fromstring("<root xmlns='http://localhost' />"))
Explanation: As you can see, errors are detailed enough so you can correct your own XML, at least manually.
1.3.3 Node properties and methods
Quick explanation : Methods and properties are something special in Python and other programming languages. Unlike traditional functions (len()) and keys of dictionaries (a["b"]), they are part of something bigger.
Methods : Ever seen something such as a.method() ? Yes, you did with .split(), .join(), etc. Functions following a variable with a dot are called methods because they are an extension of the variable type. eh split() and join() are extensions of string objects, and they use their value as argument.
Properties or Attributes : Such as dictionary keys, properties are indexed values of an object, but instead of using the syntax made of square brackets, you just put the name of the key after a dot : a.property
Warning : namespaces : In lxml, namespaces are expressed using the Clark notation. This mean that, if a namespace defines a node, this node will be named using the following syntax "{namespace}tagname. Here is an example :
End of explanation
# First, we will need some xml
xml = 
<div type="Book" n="1">
    <l n="1">Arma virumque cano, Troiae qui primus ab oris</l>
    <tei:l n="2" xmlns:tei="http://www.tei-c.org/ns/1.0">Italiam, fato profugus, Laviniaque venit</tei:l>
    <l n="3">litora, multum ille et terris iactatus et alto</l>
    <l n="4">vi superum saevae memorem Iunonis ob iram;</l>
    <l n="5">multa quoque et bello passus, dum conderet urbem,</l>
    <l n="6">inferretque deos Latio, genus unde Latinum,</l>
    <l n="7">Albanique patres, atque altae moenia Romae.</l>
</div>
div = etree.fromstring(xml)
print(parsed)
Explanation: You can do plenty of things using lxml and access properties or methods of nodes, here is an overview of reading functionalities offered by lxml :
Let's see what that means in real life :
End of explanation
type_div = div.get("type")
print(type_div)
print(div.get("n"))
# If we want a dictionary of attributes
print(div.attrib)
attributes_div = dict(div.attrib)
print(attributes_div)
# Of if we want a list
list_attributes_div = div.items()
print(list_attributes_div)
Explanation: If we want to retrieve the attributes of our div, we can do as follow :
End of explanation
children = div.getchildren()
print(children)
line_1 = children[0] # Because it's a list we can access children through index
print(line_1)
Explanation: Great ! We accessed our first information using lxml ! Now, how about getting somewhere other than the root tag ? To do so, there are two ways :
getchildren() will returns a list of children tags, such as div.
list(div) will transform div in a list of children.
Both syntaxes return the same results, so it's up to you to decide which one you prefer.
End of explanation
print(line_1.text)
Explanation: Now that we have access to our children, we can have access to their text :
End of explanation
#   <tei:l n="2" xmlns:tei="http://www.tei-c.org/ns/1.0">Italiam, fato profugus, Laviniaque venit</tei:l>
line_2 = children[1]
print(line_2.nsmap)
print(line_2.prefix)
print(line_2.tag)
Explanation: Ok, we are now able to get some stuff done. Remember the namespace naming ? Sometimes it's useful to retrieve namespaces and their prefix :
End of explanation
# We generate some xml and parse it
## TODO 
xml = <div>
            <l n="1">
                <p>Text</p> 
                <p>new p</p>
                followed
                <test>
                    <p>p3</p>
                </test>
            </l>
            <l n="2">
                by line two
            </l>
            <p>test</p>
            <p><l n="3"> line 3</l></p>
        </div>
div = etree.fromstring(xml)
print(div)
# When doing an xpath, the results will be a list
print("-"*20)
ps = div.xpath("/div/l")
for p in ps:
    print(p)
print("-"*20)
# print(ps)
print([value.values()[0] for value in ps])
print(ps[0].text == "Text")
Explanation: What you've learned :
How to parse a xml file or a string representing xml through etree.parse() and etree.fromstring()
How to configure the way xml is parsed with etree.XMLParser()
What is an attribute and a method
Properties and methods of a node
XMLParseError handling
Clark's notation for namespaces and tags.
1.4 . XPath and XSLT with lxml
1.4.1 XPath
XPath is a powerful tool for traversing an xml tree. XML is made of nodes such as tags, comments, texts. These nodes have attributes that can be used to identify them. For example, with the following xml :
&lt;div&gt;&lt;l n="1"&gt;&lt;p&gt;Text&lt;/p&gt; followed&lt;/l&gt;&lt;l n="2"&gt;by line two&lt;/div&gt;
the node p will be accessible by /div/l[@n="1"]/p. LXML has great support for complex XPath, which makes it the best friend of Humanists dealing with xml :
End of explanation
print(div.xpath("//l"))
Explanation: As you can see, the xpath returns a list. This behaviour is intended, since an xpath can retrieve more than one item :
End of explanation
# We assign our first line to a variable
line_1 = div.xpath("//l")[0]
#print(dir(line_1))
print(line_1.attrib['n'])
# We look for p
print(line_1.xpath("p")) # This works
print(line_1.xpath("./p")) # This works too
print(line_1.xpath(".//p")) # This still works 
print(line_1.xpath("//p")) # entire doc
Explanation: You see ? The xpath //l returns two elements, just like python does in a list. Now, let's apply some xpath to the children and see what happens :
End of explanation
root.xpath("wrong:xpath:never:works")
Explanation: As you can see, you can do xpath from any node in lxml. One important thing though : xpath //tagname will return to the root if you do not add a dot in front of it such as .//tagname. This is really important to remember, because most xpath resolvers do not behave this way.
Another point to kepe in mind : if you write your xpath incorrectly, Python will raise an *XPathEvalError * error
End of explanation
# We create a valid xml object
xml = <root>
<tag xmlns="http://localhost">Text</tag>
<tei:tag xmlns:tei="http://www.tei-c.org/ns/1.0">Other text</tei:tag>
<teiTwo:tag xmlns:teiTwo="http://www.tei-c.org/ns/2.0">Other text</teiTwo:tag>
</root>
root = etree.fromstring(xml)
# We register every namespaces in a dictionary using prefix as keys :
ns = {
    "local" : "http://localhost", # Even if this namespace had no prefix, we can register one for it
    "tei" : "http://www.tei-c.org/ns/1.0",
    "two": "http://www.tei-c.org/ns/2.0"
}
print([d.text for namespace in ns 
       for d in root.xpath("//{namespace}:tag".format(namespace=namespace), 
                           namespaces=ns) ])
Explanation: Xpath with namespaces and prefix
As you've seen, lxml use Clark's naming convention for expressing namespaces. This is extremely important regarding xpath, because you will be able to retrieve a node using it under certain conditions :
End of explanation
# Here is an xml containing an xsl: for each text node of an xml file in the xpath /humanities/field,
#     this will return a node <name> with the text inside
xslt_root = etree.fromstring(
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
        <fields><xsl:apply-templates /></fields>
    </xsl:template>
    <xsl:template match="/humanities/field">
        <name><xsl:value-of select="./text()" /></name>
    </xsl:template>
</xsl:stylesheet>)
# We transform our document to an xsl 
xslt = etree.XSLT(xslt_root)
# We create some xml we need to change 
xml = <humanities>
    <field>History</field>
    <field>Classics</field>
    <field>French</field>
    <field>German</field>
</humanities>
parsed_xml = etree.fromstring(xml)
# And now we process our xml :
transformed = xslt(parsed_xml)
print(transformed)
Explanation: What you have learned :
Each node and xml document has an .xpath() method which takes as its first parameter xpath
Method xpath() always returns a list, even for a single result
Method xpath() will return to the root when you don't prefix your // with a dot.
An incorrect XPath will issue a XPathEvalError
Method xpath() accepts a namespaces argument : you should enter a dictionary where keys are prefixes and values namespaces
Unlike findall(), xpath() does not accept Clark's notation
1.4.2 XSLT
XSLT stands for Extensible Stylesheet Language Transformations. It's an xml-based language made for transforming xml documents to xml or other formats such as LaTeX and HTML. XSLT is really powerful when dealing with similarly formated data. It's far easier to transform 100 documents with the exact same structure via XSLT than in Python or any other language.
While Python is great at dealing with weird transformations of xml, the presence of XSLT in Python allows you to create production chains without leaving your favorite IDE.
To do some XSL, lxml needs two things : first, an xml document representing the xsl that will be parsed and entered into the function etree.XSLT(), and second, a document to transform.
End of explanation
print(type(transformed))
print(type(parsed_xml))
Explanation: Did you see what happened ? We used xslt(xml). etree.XSLT() transforms a xsl document into a function, which then takes one parameter (in this case an xml document). But can you figure out what this returns ? Let's ask Python :
End of explanation
print(transformed.xpath("//name"))
Explanation: The result is not of the same type of element we usually have, even though it does share most of its methods and attributes :
End of explanation
string_result = str(transformed)
print(string_result)
Explanation: And has something more : you can change its type to string !
End of explanation
# Here is an xml containing an xsl: for each text node of an xml file in the xpath /humanities/field,
#     this will return a node <name> with the text inside
xslt_root = etree.fromstring(
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:param name="n" />
    <xsl:template match="/humanities">
        <fields>
            <xsl:attribute name="n">
                <xsl:value-of select="$n"/>
            </xsl:attribute>
            <xsl:apply-templates select="field"/>
        </fields>
    </xsl:template>
    <xsl:template match="/humanities/field">
        <name><xsl:value-of select="./text()" /></name>
    </xsl:template>
</xsl:stylesheet>)
# We transform our document to an xsl 
xslt = etree.XSLT(xslt_root)
# We create some xml we need to change 
xml = <humanities>
    <category>Humanities</category>
    <field>History</field>
    <field>Classics</field>
    <field>French</field>
    <field>German</field>
</humanities>
parsed_xml = etree.fromstring(xml)
# And now we process our xml :
transformed = xslt(parsed_xml, n="'Humanities'") # Note that for a string, we encapsulate it within single quotes
print(transformed)
# Be aware that you can use xpath as a value for the argument, though it can be rather complex sometimes
transformed = xslt(parsed_xml, n=etree.XPath("//category/text()"))
print(transformed)
Explanation: XSLT is more complex than just inputing xml. You can do XSLT using parameters as well. In this case, your parameters will be accessibles as a named argument to the generated function. If your XSL has a name xsl-param, the function given back by etree.XSLT will have a name argument :
End of explanation
from xml.etree import ElementTree
with open('data/books.xml', 'rt') as f:
    tree = ElementTree.parse(f)
print(tree)
Explanation: 2. Using ElementTree
End of explanation
from xml.etree import ElementTree
with open('data/books.xml', 'r') as f:
    tree = ElementTree.parse(f)
# print(dir(tree))
for node in tree.iter():
    print (node.tag, node.attrib)
    print("-----")
# from xml.etree import ElementTree
# with open('data/books.xml', 'r') as f:
#     tree = ElementTree.parse(f)
# # print(dir(tree))
# for node in tree.iter():
#     print (node.tag, node.attrib)
#     print("-----")
### To print only the groups of names and feed URLs for the podcasts, 
# leaving out of all of the data in the header section by iterating 
# over only the outline nodes and print the text and xmlUrl attributes.
from xml.etree import ElementTree
with open('data/podcasts.opml', 'rt') as f:
    tree = ElementTree.parse(f)
print(len( list(tree.iter('outline'))))
for node in tree.iter('outline'):
    name = node.attrib.get('text')
    url = node.attrib.get('xmlUrl')
    if name and url:
        print ('\t%s :: %s' % (name, url))
    else:
        print (name)
Explanation: 2.1 Traversing the Parsed Tree
To visit all of the children in order, use iter() to create a generator that iterates over the ElementTree instance.
End of explanation
for node in tree.findall('.//outline'):
    url = node.attrib.get('xmlUrl')
    if url:
        print( url)
    else:
        print(node.attrib.get("text"))
print(dir(tree))
print(tree.getroot)
Explanation: 2.1.1 Finding Nodes in a Document¶
Walking the entire tree like this searching for relevant nodes can be error prone. The example above had to look at each outline node to determine if it was a group (nodes with only a text attribute) or podcast (with both text and xmlUrl). To produce a simple list of the podcast feed URLs, without names or groups, for a podcast downloader application, the logic could be simplified using findall() to look for nodes with more descriptive search characteristics.
As a first pass at converting the above example, we can construct an XPath argument to look for all outline nodes.
End of explanation
for node in tree.findall('.//outline/outline'):
    url = node.attrib.get('xmlUrl')
    print (url)
Explanation: Another version can take advantage of the fact that the outline nodes are only nested two levels deep. Changing the search path to .//outline/outline mean the loop will process only the second level of outline nodes.
End of explanation
from xml.etree import ElementTree
with open('data/data.xml', 'rt') as f:
    tree = ElementTree.parse(f)
node = tree.find('./with_attributes')
print (node.tag)
for name, value in sorted(node.attrib.items()):
    print ('  %-4s = "%s"' % (name, value))
for path in [ './child', './child_with_tail' ]:
    node = tree.find(path)
    print(node.tag)
    print ('  child node text:', node.text)
    print ('  and tail text  :', node.tail)
Explanation: 2.1.2 Parsed Node Attributes
The items returned by findall() and iter() are Element objects, each representing a node in the XML parse tree. Each Element has attributes for accessing data pulled out of the XML. This can be illustrated with a somewhat more contrived example input file, data.xml:
End of explanation
from xml.etree.ElementTree import XML
parsed = XML('''
<root>
  <group>
    <child id="a">This is child "a".</child>
    <child id="b">This is child "b".</child>
  </group>
  <group>
    <child id="c">This is child "c".</child>
  </group>
</root>
''')
print ('parsed =', parsed)
for elem in parsed:
    print (elem.tag)
    if elem.text is not None and elem.text.strip():
        print ('  text: "%s"' % elem.text)
    if elem.tail is not None and elem.tail.strip():
        print ('  tail: "%s"' % elem.tail)
    for name, value in sorted(elem.attrib.items()):
        print('  %-4s = "%s"' % (name, value))
    print
from xml.etree.ElementTree import Element, tostring
top = Element('top')
children = [
    Element('child', num=str(i))
    for i in range(3)
]
top.extend(children)
print(top)
Explanation: 2.1.3 Parsing Strings
To work with smaller bits of XML text, especially string literals as might be embedded in the source of a program, use XML() and the string containing the XML to be parsed as the only argument.
End of explanation
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