Using elementtree: replacing nodes

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  • André
    #1

    Using elementtree: replacing nodes

    I've started using elementtree and don't understand how to use it to
    manipulate and replace nodes. I know how to do this using a simple,
    but inefficient parser I wrote, but I'd rather learn to use a better
    tool - especially as it is to be added to the standard library.

    I'll use a simple, but representative example. Suppose I have the
    following text, where I inserted blank lines to isolate the part I want
    to manipulate.
    =============== ====
    <html>
    <body>
    <p>
    This is some text.
    </p>

    <pre class="text">
    a = 6*7
    print a
    </pre>

    <p>
    Done.
    </p>
    </body>
    </html>
    =============== =====
    Now, I would like to find all <pre> tags of the "text" class and
    1. change the class value
    2. append another node ( <textarea> )
    3. surround the both nodes by a third one ( <form> )
    =============== ===
    <html>
    <body>
    <p>
    This is some text.
    <p>

    <form>
    <pre class="text2">
    a = 6*7
    print a
    </pre>
    <textarea cols=80 name="code">
    </textarea>
    <input type="submit"></input>
    </form>

    <p>
    Done.
    </p>
    </body>
    </html>
    ===============

    Any help would be appreciated.
    André

    Tags: None
    • Fredrik Lundh
      #2
      Re: Using elementtree: replacing nodes

      André wrote:
      [color=blue]
      > I've started using elementtree and don't understand how to use it to
      > manipulate and replace nodes. I know how to do this using a simple,
      > but inefficient parser I wrote, but I'd rather learn to use a better
      > tool - especially as it is to be added to the standard library.[/color]
      [color=blue]
      > Now, I would like to find all <pre> tags of the "text" class and[/color]

      for pre in elem.getiterato r("pre"):

      or

      for pre in elem.findall(".//pre"):
      [color=blue]
      > 1. change the class value[/color]

      pre.set("class" , "value")
      [color=blue]
      > 2. append another node ( <textarea> )
      > 3. surround the both nodes by a third one ( <form> )[/color]

      or in other words,

      2. replace the <pre> with a <form> element that contains some
      new contents derived from the old element

      # 1) build the new form
      form = Element("form")
      e = SubElement(form , "pre")
      e.set("class", "text2")
      e.text = pre.text
      e = SubElement(form , "textarea", cols=80, name="code")
      e = SubElement(form , "input", type="submit")

      # 2) mutate the pre element
      pre.clear()
      pre.tag = "form"
      pre[:] = [form]

      for harder cases, a common pattern is:

      for parent in elem.getiterato r():
      for index, child in enumerate(paren t.findall("pre" )):
      # the code in here can manipulate parent[i] and child

      another approach is to build a parent map; see the parent_map code
      at

      http://effbot.org/zone/element.htm#the-element-type


      </F>



        Comment

        • André
          #3
          Re: Using elementtree: replacing nodes

          Fredrik Lundh wrote:[color=blue]
          > André wrote:
          >[color=green]
          > > I've started using elementtree and don't understand how to use it to
          > > manipulate and replace nodes.[/color][/color]

          [snip]
          It was mostly the following step which I couldn`t figure out...
          [color=blue]
          > # 2) mutate the pre element
          > pre.clear()
          > pre.tag = "form"
          > pre[:] = [form]
          >[/color]
          [snip]
          [color=blue]
          > another approach is to build a parent map; see the parent_map code
          > at
          >
          > http://effbot.org/zone/element.htm#the-element-type
          > [/color]


          Thanks!
          [color=blue]
          > </F>[/color]

            Comment

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