Parsing a file with multiple xmls in it

Question

Is there a way to parse a file which contains multiple xmls in it?

eg., if I have a file called stocks.xml and within the stocks.xml i have more than one xml content

Answer 1

You should see this python program by Michiel de Hoon And if you want to parse multiple files, then a rule to detect that we are in other xml must be developed, for example,at first you read <stocks> .... and at the end you must reead </stocks> when you find that then if there is something else,well, continue reading and do the same parser until reach eof.

# Copyright 2008 by Michiel de Hoon.  All rights reserved.
# This code is part of the Biopython distribution and governed by its
# license.  Please see the LICENSE file that should have been included
# as part of this package.

"""Parser for XML results returned by NCBI's Entrez Utilities. This
parser is used by the read() function in Bio.Entrez, and is not intended
be used directly.
"""

# The question is how to represent an XML file as Python objects. Some
# XML files returned by NCBI look like lists, others look like dictionaries,
# and others look like a mix of lists and dictionaries.
#
# My approach is to classify each possible element in the XML as a plain
# string, an integer, a list, a dictionary, or a structure. The latter is a
# dictionary where the same key can occur multiple times; in Python, it is
# represented as a dictionary where that key occurs once, pointing to a list
# of values found in the XML file.
#
# The parser then goes through the XML and creates the appropriate Python
# object for each element. The different levels encountered in the XML are
# preserved on the Python side. So a subelement of a subelement of an element
# is a value in a dictionary that is stored in a list which is a value in
# some other dictionary (or a value in a list which itself belongs to a list
# which is a value in a dictionary, and so on). Attributes encountered in 
# the XML are stored as a dictionary in a member .attributes of each element,
# and the tag name is saved in a member .tag.
#
# To decide which kind of Python object corresponds to each element in the
# XML, the parser analyzes the DTD referred at the top of (almost) every
# XML file returned by the Entrez Utilities. This is preferred over a hand-
# written solution, since the number of DTDs is rather large and their
# contents may change over time. About half the code in this parser deals
# wih parsing the DTD, and the other half with the XML itself.


import os.path
import urlparse
import urllib
import warnings
from xml.parsers import expat

# The following four classes are used to add a member .attributes to integers,
# strings, lists, and dictionaries, respectively.

class IntegerElement(int):
    def __repr__(self):
        text = int.__repr__(self)
        try:
            attributes = self.attributes
        except AttributeError:
            return text
        return "IntegerElement(%s, attributes=%s)" % (text, repr(attributes))

class StringElement(str):
    def __repr__(self):
        text = str.__repr__(self)
        try:
            attributes = self.attributes
        except AttributeError:
            return text
        return "StringElement(%s, attributes=%s)" % (text, repr(attributes))

class UnicodeElement(unicode):
    def __repr__(self):
        text = unicode.__repr__(self)
        try:
            attributes = self.attributes
        except AttributeError:
            return text
        return "UnicodeElement(%s, attributes=%s)" % (text, repr(attributes))

class ListElement(list):
    def __repr__(self):
        text = list.__repr__(self)
        try:
            attributes = self.attributes
        except AttributeError:
            return text
        return "ListElement(%s, attributes=%s)" % (text, repr(attributes))

class DictionaryElement(dict):
    def __repr__(self):
        text = dict.__repr__(self)
        try:
            attributes = self.attributes
        except AttributeError:
            return text
        return "DictElement(%s, attributes=%s)" % (text, repr(attributes))

# A StructureElement is like a dictionary, but some of its keys can have
# multiple values associated with it. These values are stored in a list
# under each key.
class StructureElement(dict):
    def __init__(self, keys):
        dict.__init__(self)
        for key in keys:
            dict.__setitem__(self, key, [])
        self.listkeys = keys
    def __setitem__(self, key, value):
        if key in self.listkeys:
            self[key].append(value)
        else:
            dict.__setitem__(self, key, value)
    def __repr__(self):
        text = dict.__repr__(self)
        try:
            attributes = self.attributes
        except AttributeError:
            return text
        return "DictElement(%s, attributes=%s)" % (text, repr(attributes))


class NotXMLError(ValueError):
    def __init__(self, message):
        self.msg = message
    def __str__(self):
        return "Failed to parse the XML data (%s). Please make sure that the input data are in XML format." % self.msg


class CorruptedXMLError(ValueError):
    def __init__(self, message):
        self.msg = message
    def __str__(self):
        return "Failed to parse the XML data (%s). Please make sure that the input data are not corrupted." % self.msg


class ValidationError(ValueError):
    """Validating parsers raise this error if the parser finds a tag in the XML that is not defined in the DTD. Non-validating parsers do not raise this error. The Bio.Entrez.read and Bio.Entrez.parse functions use validating parsers by default (see those functions for more information)"""
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return "Failed to find tag '%s' in the DTD. To skip all tags that are not represented in the DTD, please call Bio.Entrez.read or Bio.Entrez.parse with validate=False." % self.name


class DataHandler:

    home = os.path.expanduser('~')
    local_dtd_dir = os.path.join(home, '.biopython', 'Bio', 'Entrez', 'DTDs')
    del home

    from Bio import Entrez
    global_dtd_dir = os.path.join(str(Entrez.__path__[0]), "DTDs")
    del Entrez

    def __init__(self, validate):
        self.stack = []
        self.errors = []
        self.integers = []
        self.strings = []
        self.lists = []
        self.dictionaries = []
        self.structures = {}
        self.items = []
        self.dtd_urls = []
        self.validating = validate
        self.parser = expat.ParserCreate(namespace_separator=" ")
        self.parser.SetParamEntityParsing(expat.XML_PARAM_ENTITY_PARSING_ALWAYS)
        self.parser.XmlDeclHandler = self.xmlDeclHandler

    def read(self, handle):
        """Set up the parser and let it parse the XML results"""
        try:
            self.parser.ParseFile(handle)
        except expat.ExpatError, e:
            if self.parser.StartElementHandler:
                # We saw the initial <!xml declaration, so we can be sure that
                # we are parsing XML data. Most likely, the XML file is
                # corrupted.
                raise CorruptedXMLError(e)
            else:
                # We have not seen the initial <!xml declaration, so probably
                # the input data is not in XML format.
                raise NotXMLError(e)
        try:
            return self.object
        except AttributeError:
            if self.parser.StartElementHandler:
                # We saw the initial <!xml declaration, and expat didn't notice
                # any errors, so self.object should be defined. If not, this is
                # a bug.
                raise RuntimeError("Failed to parse the XML file correctly, possibly due to a bug in Bio.Entrez. Please contact the Biopython developers at biopython-dev@biopython.org for assistance.")
            else:
                # We did not see the initial <!xml declaration, so probably
                # the input data is not in XML format.
                raise NotXMLError("XML declaration not found")

    def parse(self, handle):
        BLOCK = 1024
        while True:
            #Read in another block of the file...
            text = handle.read(BLOCK)
            if not text:
                # We have reached the end of the XML file
                if self.stack:
                    # No more XML data, but there is still some unfinished
                    # business
                    raise CorruptedXMLError
                try:
                    for record in self.object:
                        yield record
                except AttributeError:
                    if self.parser.StartElementHandler:
                        # We saw the initial <!xml declaration, and expat
                        # didn't notice any errors, so self.object should be
                        # defined. If not, this is a bug.
                        raise RuntimeError("Failed to parse the XML file correctly, possibly due to a bug in Bio.Entrez. Please contact the Biopython developers at biopython-dev@biopython.org for assistance.")
                    else:
                        # We did not see the initial <!xml declaration, so
                        # probably the input data is not in XML format.
                        raise NotXMLError("XML declaration not found")
                self.parser.Parse("", True)
                self.parser = None
                return

            try:
                self.parser.Parse(text, False)        
            except expat.ExpatError, e:
                if self.parser.StartElementHandler:
                    # We saw the initial <!xml declaration, so we can be sure
                    # that we are parsing XML data. Most likely, the XML file
                    # is corrupted.
                    raise CorruptedXMLError(e)
                else:
                    # We have not seen the initial <!xml declaration, so
                    # probably the input data is not in XML format.
                    raise NotXMLError(e)

            if not self.stack:
                # Haven't read enough from the XML file yet
                continue

            records = self.stack[0]
            if not isinstance(records, list):
                raise ValueError("The XML file does not represent a list. Please use Entrez.read instead of Entrez.parse")
            while len(records) > 1: # Then the top record is finished
                record = records.pop(0)
                yield record

    def xmlDeclHandler(self, version, encoding, standalone):
        # XML declaration found; set the handlers
        self.parser.StartElementHandler = self.startElementHandler
        self.parser.EndElementHandler = self.endElementHandler
        self.parser.CharacterDataHandler = self.characterDataHandler
        self.parser.ExternalEntityRefHandler = self.externalEntityRefHandler
        self.parser.StartNamespaceDeclHandler = self.startNamespaceDeclHandler

    def startNamespaceDeclHandler(self, prefix, un):
        raise NotImplementedError("The Bio.Entrez parser cannot handle XML data that make use of XML namespaces")

    def startElementHandler(self, name, attrs):
        self.content = ""
        if name in self.lists:
            object = ListElement()
        elif name in self.dictionaries:
            object = DictionaryElement()
        elif name in self.structures:
            object = StructureElement(self.structures[name])
        elif name in self.items: # Only appears in ESummary
            name = str(attrs["Name"]) # convert from Unicode
            del attrs["Name"]
            itemtype = str(attrs["Type"]) # convert from Unicode
            del attrs["Type"]
            if itemtype=="Structure":
                object = DictionaryElement()
            elif name in ("ArticleIds", "History"):
                object = StructureElement(["pubmed", "medline"])
            elif itemtype=="List":
                object = ListElement()
            else:
                object = StringElement()
            object.itemname = name
            object.itemtype = itemtype
        elif name in self.strings + self.errors + self.integers:
            self.attributes = attrs
            return
        else:
            # Element not found in DTD
            if self.validating:
                raise ValidationError(name)
            else:
                # this will not be stored in the record
                object = ""
        if object!="":
            object.tag = name
            if attrs:
                object.attributes = dict(attrs)
            if len(self.stack)!=0:
                current = self.stack[-1]
                try:
                    current.append(object)
                except AttributeError:
                    current[name] = object
        self.stack.append(object)

    def endElementHandler(self, name):
        value = self.content
        if name in self.errors:
            if value=="":
                return
            else:
                raise RuntimeError(value)
        elif name in self.integers:
            value = IntegerElement(value)
        elif name in self.strings:
            # Convert Unicode strings to plain strings if possible
            try:
                value = StringElement(value)
            except UnicodeEncodeError:
                value = UnicodeElement(value)
        elif name in self.items:
            self.object = self.stack.pop()
            if self.object.itemtype in ("List", "Structure"):
                return
            elif self.object.itemtype=="Integer" and value:
                value = IntegerElement(value)
            else:
                # Convert Unicode strings to plain strings if possible
                try:
                    value = StringElement(value)
                except UnicodeEncodeError:
                    value = UnicodeElement(value)
            name = self.object.itemname
        else:
            self.object = self.stack.pop()
            return
        value.tag = name
        if self.attributes:
            value.attributes = dict(self.attributes)
            del self.attributes
        current = self.stack[-1]
        if current!="":
            try:
                current.append(value)
            except AttributeError:
                current[name] = value

    def characterDataHandler(self, content):
        self.content += content

    def elementDecl(self, name, model):
        """This callback function is called for each element declaration:
        <!ELEMENT       name          (...)>
        encountered in a DTD. The purpose of this function is to determine
        whether this element should be regarded as a string, integer, list
        dictionary, structure, or error."""
        if name.upper()=="ERROR":
            self.errors.append(name)
            return
        if name=='Item' and model==(expat.model.XML_CTYPE_MIXED,
                                    expat.model.XML_CQUANT_REP,
                                    None, ((expat.model.XML_CTYPE_NAME,
                                            expat.model.XML_CQUANT_NONE,
                                            'Item',
                                            ()
                                           ),
                                          )
                                   ):
            # Special case. As far as I can tell, this only occurs in the
            # eSummary DTD.
            self.items.append(name)
            return
        # First, remove ignorable parentheses around declarations
        while (model[0] in (expat.model.XML_CTYPE_SEQ,
                            expat.model.XML_CTYPE_CHOICE)
          and model[1] in (expat.model.XML_CQUANT_NONE,
                           expat.model.XML_CQUANT_OPT)
          and len(model[3])==1):
            model = model[3][0]
        # PCDATA declarations correspond to strings
        if model[0] in (expat.model.XML_CTYPE_MIXED,
                        expat.model.XML_CTYPE_EMPTY):
            self.strings.append(name)
            return
        # List-type elements
        if (model[0] in (expat.model.XML_CTYPE_CHOICE,
                         expat.model.XML_CTYPE_SEQ) and
            model[1] in (expat.model.XML_CQUANT_PLUS,
                         expat.model.XML_CQUANT_REP)):
            self.lists.append(name)
            return
        # This is the tricky case. Check which keys can occur multiple
        # times. If only one key is possible, and it can occur multiple
        # times, then this is a list. If more than one key is possible,
        # but none of them can occur multiple times, then this is a
        # dictionary. Otherwise, this is a structure.
        # In 'single' and 'multiple', we keep track which keys can occur
        # only once, and which can occur multiple times.
        single = []
        multiple = []
        # The 'count' function is called recursively to make sure all the
        # children in this model are counted. Error keys are ignored;
        # they raise an exception in Python.
        def count(model):
            quantifier, name, children = model[1:]
            if name==None:
                if quantifier in (expat.model.XML_CQUANT_PLUS,
                                  expat.model.XML_CQUANT_REP):
                    for child in children:
                        multiple.append(child[2])
                else:
                    for child in children:
                        count(child)
            elif name.upper()!="ERROR":
                if quantifier in (expat.model.XML_CQUANT_NONE,
                                  expat.model.XML_CQUANT_OPT):
                    single.append(name)
                elif quantifier in (expat.model.XML_CQUANT_PLUS,
                                    expat.model.XML_CQUANT_REP):
                    multiple.append(name)
        count(model)
        if len(single)==0 and len(multiple)==1:
            self.lists.append(name)
        elif len(multiple)==0:
            self.dictionaries.append(name)
        else:
            self.structures.update({name: multiple})

    def open_dtd_file(self, filename):
        path = os.path.join(DataHandler.local_dtd_dir, filename)
        try:
            handle = open(path, "rb")
        except IOError:
            pass
        else:
            return handle
        path = os.path.join(DataHandler.global_dtd_dir, filename)
        try:
            handle = open(path, "rb")
        except IOError:
            pass
        else:
            return handle
        return None

    def externalEntityRefHandler(self, context, base, systemId, publicId):
        """The purpose of this function is to load the DTD locally, instead
        of downloading it from the URL specified in the XML. Using the local
        DTD results in much faster parsing. If the DTD is not found locally,
        we try to download it. If new DTDs become available from NCBI,
        putting them in Bio/Entrez/DTDs will allow the parser to see them."""
        urlinfo = urlparse.urlparse(systemId)
        #Following attribute requires Python 2.5+
        #if urlinfo.scheme=='http':
        if urlinfo[0]=='http':
            # Then this is an absolute path to the DTD.
            url = systemId
        elif urlinfo[0]=='':
            # Then this is a relative path to the DTD.
            # Look at the parent URL to find the full path.
            url = self.dtd_urls[-1]
            source = os.path.dirname(url)
            url = os.path.join(source, systemId)
        self.dtd_urls.append(url)
        # First, try to load the local version of the DTD file
        location, filename = os.path.split(systemId)
        handle = self.open_dtd_file(filename)
        if not handle:
            # DTD is not available as a local file. Try accessing it through
            # the internet instead.
            message = """\
Unable to load DTD file %s.

Bio.Entrez uses NCBI's DTD files to parse XML files returned by NCBI Entrez.
Though most of NCBI's DTD files are included in the Biopython distribution,
sometimes you may find that a particular DTD file is missing. While we can
access the DTD file through the internet, the parser is much faster if the
required DTD files are available locally.

For this purpose, please download %s from

%s

and save it either in directory

%s

or in directory

%s

in order for Bio.Entrez to find it.

Alternatively, you can save %s in the directory
Bio/Entrez/DTDs in the Biopython distribution, and reinstall Biopython.

Please also inform the Biopython developers about this missing DTD, by
reporting a bug on http://bugzilla.open-bio.org/ or sign up to our mailing
list and emailing us, so that we can include it with the next release of
Biopython.

Proceeding to access the DTD file through the internet...
""" % (filename, filename, url, self.global_dtd_dir, self.local_dtd_dir, filename)
            warnings.warn(message)
            try:
                handle = urllib.urlopen(url)
            except IOError:
                raise RuntimeException("Failed to access %s at %s" % (filename, url))

        parser = self.parser.ExternalEntityParserCreate(context)
        parser.ElementDeclHandler = self.elementDecl
        parser.ParseFile(handle)
        handle.close()
        self.dtd_urls.pop()
        return 1

Answer 2

You can't have multiple XML documents in one XML file. Split the documents - composed in whatever way - into single XML files and parse them one-by-one.

Answer 3

If you can assume that each xml document begins with <?xml version="1.0" ..., simply read the file line-by-line looking for a lines that match that pattern (or, read all the data and then do a search through the data).

Once you find a line, keep it, and append subsequent lines until the next xml document is found or you hit EOF. lather, rinse, repeat.

You now have one xml document in a string. You can then parse the string using the normal XML parsing tools, or you write it to a file.

This will work fine in most cases, but of course it could fall down if one of your embedded xml documents contains data that exactly matches the same pattern as the beginning of a document. Most likely you don't have to worry about that, and if you do there are ways to avoid that with a little more cleverness.

The right solution really depends on your needs. If you're creating a general purpose must-work-at-all-times solution this might not be right for you. For real world, special purpose problems it's probably more than Good Enough, and often Good Enough is indeed Good Enough.

Answer 4

So you have a file containing multiple XML documents one after the other? Here is an example which strips out the <?xml ?> PIs and wraps the data in a root tag to parse the whole thing as a single XML document:

import re
import lxml.etree

re_strip_pi = re.compile('<\?xml [^?>]+\?>', re.M)
data = '<root>' + open('stocks.xml', 'rb').read() + '</root>'
match = re_strip_pi.search(data)
data = re_strip_pi.sub('', data)
tree = lxml.etree.fromstring(match.group() + data)
for prod in tree.xpath('//PRODUCT'):
    print prod