Python列表搜索，元素比较和消除

Question

I would like to get all elements that don't have a pair. This is a list of XML tags as read from top to bottom with brackets removed. I would like to find pairs (for ex. opening tag note and closing tag /note ), remove them from the list and then be left with tags that don't have pairs.

How do you iterate through the list, compare each tag with all other tags and say for example: aha, I found another 'note' tag that starts with forward slash?

Thanks.

Any other - better - ideas to find mismatching tags?

PS: I do want the order of the list to be preserved and if possible, equality to be used when tag is compared to another tag in the list. If 'in' operator is used it won't work because in case tag name is one letter like 'a', then search will return all elements that contain a, not exact match for 'a'.

tags = ['note', 'to', 'bbb', 'bbb', 'firstname', '/firstname', 'lastname', '/lastname', 'from', 'hello', 'hello', 'hello', 'hello', 'hello', 'l', '/from', '/to', 'elephant', 'll', 'from', '/from', 'a1', 'img', 'a2', 'from', 'from', '/from', '/from', '/a2', '/img', '/a1', 'heading', '/heading', 'body', '/body', '/note']

Answer 1

You could create a set with all the closing tags and then use that set to filter the tags.

>>> closing = set([t for t in tags if t.startswith("/")])
>>> [t for t in tags if "/" + t not in closing and t not in closing]
['bbb', 'bbb', 'hello', 'hello', 'hello', 'hello', 'hello', 'l', 'elephant', 'll']

Note, however, that this will not really respect "pairs" of tags, but just see whether there is a "closing" variant of the same tag in the list. For instance, given tags = ["a", "a", "/a"] or tags = ["a", "/a", "a"] , it will remove both instances of a from the list.

Answer 2

First part of the program gets all the tags in a list. If you notice it is the problem of finding non-matching brackets. It can be solved by considering that list as stack, and finding which tags are faulty , iterating along the way.

import re

def clean_attr(attr):
    attr_list = re.split(r'\s+', attr)
    if len(attr_list) == 1:
        return attr
    else:
        return attr_list[0] + '>'

line="""
<?xml version="1.0"?>
<catalog>
   <book id="bk101">
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth look at creating applications 
      with XML.</description>
   </book>
   <book id="bk102">
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.</description>
   </book>
   <book id="bk103">
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-11-17</publish_date>
      <description>After the collapse of a nanotechnology 
      society in England, the young survivors lay the 
      foundation for a new society.</description>
   </book>
   <book id="bk104">
      <author>Corets, Eva</author>
      <title>Oberon's Legacy</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-03-10</publish_date>
      <description>In post-apocalypse England, the mysterious 
      agent known only as Oberon helps to create a new life 
      for the inhabitants of London. Sequel to Maeve 
      Ascendant.</description>
   </book>
   <book id="bk105">
      <author>Corets, Eva</author>
      <title>The Sundered Grail</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-09-10</publish_date>
      <description>The two daughters of Maeve, half-sisters, 
      battle one another for control of England. Sequel to 
      Oberon's Legacy.</description>
   </book>
   <book id="bk106">
      <author>Randall, Cynthia</author>
      <title>Lover Birds</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-09-02</publish_date>
      <description>When Carla meets Paul at an ornithology 
      conference, tempers fly as feathers get ruffled.</description>
   </book>
   <book id="bk107">
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>A deep sea diver finds true love twenty 
      thousand leagues beneath the sea.</description>
   </book>
   <book id="bk108">
      <author>Knorr, Stefan</author>
      <title>Creepy Crawlies</title>
      <genre>Horror</genre>
      <price>4.95</price>
      <publish_date>2000-12-06</publish_date>
      <description>An anthology of horror stories about roaches,
      centipedes, scorpions  and other insects.</description>
   </book>
   <book id="bk109">
      <author>Kress, Peter</author>
      <title>Paradox Lost</title>
      <genre>Science Fiction</genre>
      <price>6.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>After an inadvertant trip through a Heisenberg
      Uncertainty Device, James Salway discovers the problems 
      of being quantum.</description>
   </book>
   <book id="bk110">
      <author>O'Brien, Tim</author>
      <title>Microsoft .NET: The Programming Bible</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-09</publish_date>
      <description>Microsoft's .NET initiative is explored in 
      detail in this deep programmer's reference.</description>
   </book>
      <author>O'Brien, Tim</author>
      <title>MSXML3: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-01</publish_date>
      <description>The Microsoft MSXML3 parser is covered in 
      detail, with attention to XML DOM interfaces, XSLT processing, 
      SAX and more.</description>
   </book>
   <book id="bk112">
      <author>Galos, Mike</author>
      <title>Visual Studio 7: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>49.95</price>
      <publish_date>2001-04-16</publish_date>
      <description>Microsoft Visual Studio 7 is explored in depth,
      looking at how Visual Basic, Visual C++, C#, and ASP+ are 
      integrated into a comprehensive development 
      environment.
   </book>
</catalog>

"""
attr_open = re.findall(r'<[\w+\s=\"]+>', line)
attr_closed = re.findall(r'<\/\w+>', line)
all_attrs = re.findall(r'<[\w+\s=\"]+>|<\/\w+>', line)

all_attrs_cleaned = map(clean_attr, all_attrs)

# print all_attrs_cleaned

list_as_stack = []
not_closed = []
all_attrs_cleaned = iter(all_attrs_cleaned)

an_attr = all_attrs_cleaned.next()

try:
    while all_attrs_cleaned:
        if not an_attr.startswith('</'):
            list_as_stack.append(an_attr)
            an_attr = all_attrs_cleaned.next()
        else:
            temp = list_as_stack[-1]
            if re.search(r'\w+', temp).group(0) == re.search(r'\w+', an_attr).group(0):
                list_as_stack.pop()
                an_attr = all_attrs_cleaned.next()
            else:
                if len(list_as_stack) != 0:
                    not_closed.append(an_attr)  
                an_attr = all_attrs_cleaned.next()
except Exception:
    print "Stop Iter"

print list_as_stack
print not_closed

In above program, the first array tells you, which tags are not closed, and second array tells you which closing tags do not have opening tags.