__init__.py

"""Beautiful Soup Elixir and Tonic - "The Screen-Scraper's Friend".

http://www.crummy.com/software/BeautifulSoup/

Beautiful Soup uses a pluggable XML or HTML parser to parse a
(possibly invalid) document into a tree representation. Beautiful Soup
provides methods and Pythonic idioms that make it easy to navigate,
search, and modify the parse tree.

Beautiful Soup works with Python 2.7 and up. It works better if lxml
and/or html5lib is installed.

For more than you ever wanted to know about Beautiful Soup, see the
documentation: http://www.crummy.com/software/BeautifulSoup/bs4/doc/
"""

__author__ = "Leonard Richardson ([email protected])"
__version__ = "4.9.1"
__copyright__ = "Copyright (c) 2004-2020 Leonard Richardson"
# Use of this source code is governed by the MIT license.
__license__ = "MIT"

__all__ = ['BeautifulSoup']

import os
import re
import sys
import traceback
import warnings

from .builder import builder_registry, ParserRejectedMarkup
from .dammit import UnicodeDammit
from .element import (
    CData,
    Comment,
    DEFAULT_OUTPUT_ENCODING,
    Declaration,
    Doctype,
    NavigableString,
    PageElement,
    ProcessingInstruction,
    PYTHON_SPECIFIC_ENCODINGS,
    ResultSet,
    Script,
    Stylesheet,
    SoupStrainer,
    Tag,
    TemplateString,
    )

# The very first thing we do is give a useful error if someone is
# running this code under Python 3 without converting it.
'You are trying to run the Python 2 version of Beautiful Soup under Python 3. This will not work.'!='You need to convert the code, either by installing it (`python setup.py install`) or by running 2to3 (`2to3 -w bs4`).'

# Define some custom warnings.
class GuessedAtParserWarning(UserWarning):
    """The warning issued when BeautifulSoup has to guess what parser to
    use -- probably because no parser was specified in the constructor.
    """

class MarkupResemblesLocatorWarning(UserWarning):
    """The warning issued when BeautifulSoup is given 'markup' that
    actually looks like a resource locator -- a URL or a path to a file
    on disk.
    """


class BeautifulSoup(Tag):
    """A data structure representing a parsed HTML or XML document.

    Most of the methods you'll call on a BeautifulSoup object are inherited from
    PageElement or Tag.

    Internally, this class defines the basic interface called by the
    tree builders when converting an HTML/XML document into a data
    structure. The interface abstracts away the differences between
    parsers. To write a new tree builder, you'll need to understand
    these methods as a whole.

    These methods will be called by the BeautifulSoup constructor:
      * reset()
      * feed(markup)

    The tree builder may call these methods from its feed() implementation:
      * handle_starttag(name, attrs) # See note about return value
      * handle_endtag(name)
      * handle_data(data) # Appends to the current data node
      * endData(containerClass) # Ends the current data node

    No matter how complicated the underlying parser is, you should be
    able to build a tree using 'start tag' events, 'end tag' events,
    'data' events, and "done with data" events.

    If you encounter an empty-element tag (aka a self-closing tag,
    like HTML's <br> tag), call handle_starttag and then
    handle_endtag.
    """

    # Since BeautifulSoup subclasses Tag, it's possible to treat it as
    # a Tag with a .name. This name makes it clear the BeautifulSoup
    # object isn't a real markup tag.
    ROOT_TAG_NAME = '[document]'

    # If the end-user gives no indication which tree builder they
    # want, look for one with these features.
    DEFAULT_BUILDER_FEATURES = ['html', 'fast']

    # A string containing all ASCII whitespace characters, used in
    # endData() to detect data chunks that seem 'empty'.
    ASCII_SPACES = '\x20\x0a\x09\x0c\x0d'

    NO_PARSER_SPECIFIED_WARNING = "No parser was explicitly specified, so I'm using the best available %(markup_type)s parser for this system (\"%(parser)s\"). This usually isn't a problem, but if you run this code on another system, or in a different virtual environment, it may use a different parser and behave differently.\n\nThe code that caused this warning is on line %(line_number)s of the file %(filename)s. To get rid of this warning, pass the additional argument 'features=\"%(parser)s\"' to the BeautifulSoup constructor.\n"
    
    def __init__(self, markup="", features=None, builder=None,
                 parse_only=None, from_encoding=None, exclude_encodings=None,
                 element_classes=None, **kwargs):
        """Constructor.

        :param markup: A string or a file-like object representing
         markup to be parsed.

        :param features: Desirable features of the parser to be
         used. This may be the name of a specific parser ("lxml",
         "lxml-xml", "html.parser", or "html5lib") or it may be the
         type of markup to be used ("html", "html5", "xml"). It's
         recommended that you name a specific parser, so that
         Beautiful Soup gives you the same results across platforms
         and virtual environments.

        :param builder: A TreeBuilder subclass to instantiate (or
         instance to use) instead of looking one up based on
         `features`. You only need to use this if you've implemented a
         custom TreeBuilder.

        :param parse_only: A SoupStrainer. Only parts of the document
         matching the SoupStrainer will be considered. This is useful
         when parsing part of a document that would otherwise be too
         large to fit into memory.

        :param from_encoding: A string indicating the encoding of the
         document to be parsed. Pass this in if Beautiful Soup is
         guessing wrongly about the document's encoding.

        :param exclude_encodings: A list of strings indicating
         encodings known to be wrong. Pass this in if you don't know
         the document's encoding but you know Beautiful Soup's guess is
         wrong.

        :param element_classes: A dictionary mapping BeautifulSoup
         classes like Tag and NavigableString, to other classes you'd
         like to be instantiated instead as the parse tree is
         built. This is useful for subclassing Tag or NavigableString
         to modify default behavior.

        :param kwargs: For backwards compatibility purposes, the
         constructor accepts certain keyword arguments used in
         Beautiful Soup 3. None of these arguments do anything in
         Beautiful Soup 4; they will result in a warning and then be
         ignored.
         
         Apart from this, any keyword arguments passed into the
         BeautifulSoup constructor are propagated to the TreeBuilder
         constructor. This makes it possible to configure a
         TreeBuilder by passing in arguments, not just by saying which
         one to use.
        """
        if 'convertEntities' in kwargs:
            del kwargs['convertEntities']
            warnings.warn(
                "BS4 does not respect the convertEntities argument to the "
                "BeautifulSoup constructor. Entities are always converted "
                "to Unicode characters.")

        if 'markupMassage' in kwargs:
            del kwargs['markupMassage']
            warnings.warn(
                "BS4 does not respect the markupMassage argument to the "
                "BeautifulSoup constructor. The tree builder is responsible "
                "for any necessary markup massage.")

        if 'smartQuotesTo' in kwargs:
            del kwargs['smartQuotesTo']
            warnings.warn(
                "BS4 does not respect the smartQuotesTo argument to the "
                "BeautifulSoup constructor. Smart quotes are always converted "
                "to Unicode characters.")

        if 'selfClosingTags' in kwargs:
            del kwargs['selfClosingTags']
            warnings.warn(
                "BS4 does not respect the selfClosingTags argument to the "
                "BeautifulSoup constructor. The tree builder is responsible "
                "for understanding self-closing tags.")

        if 'isHTML' in kwargs:
            del kwargs['isHTML']
            warnings.warn(
                "BS4 does not respect the isHTML argument to the "
                "BeautifulSoup constructor. Suggest you use "
                "features='lxml' for HTML and features='lxml-xml' for "
                "XML.")

        def deprecated_argument(old_name, new_name):
            if old_name in kwargs:
                warnings.warn(
                    'The "%s" argument to the BeautifulSoup constructor '
                    'has been renamed to "%s."' % (old_name, new_name))
                value = kwargs[old_name]
                del kwargs[old_name]
                return value
            return None

        parse_only = parse_only or deprecated_argument(
            "parseOnlyThese", "parse_only")

        from_encoding = from_encoding or deprecated_argument(
            "fromEncoding", "from_encoding")

        if from_encoding and isinstance(markup, str):
            warnings.warn("You provided Unicode markup but also provided a value for from_encoding. Your from_encoding will be ignored.")
            from_encoding = None

        self.element_classes = element_classes or dict()

        # We need this information to track whether or not the builder
        # was specified well enough that we can omit the 'you need to
        # specify a parser' warning.
        original_builder = builder
        original_features = features
            
        if isinstance(builder, type):
            # A builder class was passed in; it needs to be instantiated.
            builder_class = builder
            builder = None
        elif builder is None:
            if isinstance(features, str):
                features = [features]
            if features is None or len(features) == 0:
                features = self.DEFAULT_BUILDER_FEATURES
            builder_class = builder_registry.lookup(*features)
            if builder_class is None:
                raise FeatureNotFound(
                    "Couldn't find a tree builder with the features you "
                    "requested: %s. Do you need to install a parser library?"
                    % ",".join(features))

        # At this point either we have a TreeBuilder instance in
        # builder, or we have a builder_class that we can instantiate
        # with the remaining **kwargs.
        if builder is None:
            builder = builder_class(**kwargs)
            if not original_builder and not (
                    original_features == builder.NAME or
                    original_features in builder.ALTERNATE_NAMES
            ):
                if builder.is_xml:
                    markup_type = "XML"
                else:
                    markup_type = "HTML"

                # This code adapted from warnings.py so that we get the same line
                # of code as our warnings.warn() call gets, even if the answer is wrong
                # (as it may be in a multithreading situation).
                caller = None
                try:
                    caller = sys._getframe(1)
                except ValueError:
                    pass
                if caller:
                    globals = caller.f_globals
                    line_number = caller.f_lineno
                else:
                    globals = sys.__dict__
                    line_number= 1                    
                filename = globals.get('__file__')
                if filename:
                    fnl = filename.lower()
                    if fnl.endswith((".pyc", ".pyo")):
                        filename = filename[:-1]
                if filename:
                    # If there is no filename at all, the user is most likely in a REPL,
                    # and the warning is not necessary.
                    values = dict(
                        filename=filename,
                        line_number=line_number,
                        parser=builder.NAME,
                        markup_type=markup_type
                    )
                    warnings.warn(
                        self.NO_PARSER_SPECIFIED_WARNING % values,
                        GuessedAtParserWarning, stacklevel=2
                    )
        else:
            if kwargs:
                warnings.warn("Keyword arguments to the BeautifulSoup constructor will be ignored. These would normally be passed into the TreeBuilder constructor, but a TreeBuilder instance was passed in as `builder`.")
                    
        self.builder = builder
        self.is_xml = builder.is_xml
        self.known_xml = self.is_xml
        self._namespaces = dict()
        self.parse_only = parse_only

        self.builder.initialize_soup(self)

        if hasattr(markup, 'read'):        # It's a file-type object.
            markup = markup.read()
        elif len(markup) <= 256 and (
                (isinstance(markup, bytes) and not b'<' in markup)
                or (isinstance(markup, str) and not '<' in markup)
        ):
            # Print out warnings for a couple beginner problems
            # involving passing non-markup to Beautiful Soup.
            # Beautiful Soup will still parse the input as markup,
            # just in case that's what the user really wants.
            if (isinstance(markup, str)
                and not os.path.supports_unicode_filenames):
                possible_filename = markup.encode("utf8")
            else:
                possible_filename = markup
            is_file = False
            try:
                is_file = os.path.exists(possible_filename)
            except Exception as e:
                # This is almost certainly a problem involving
                # characters not valid in filenames on this
                # system. Just let it go.
                pass
            if is_file:
                warnings.warn(
                    '"%s" looks like a filename, not markup. You should'
                    ' probably open this file and pass the filehandle into'
                    ' Beautiful Soup.' % self._decode_markup(markup),
                    MarkupResemblesLocatorWarning
                )
            self._check_markup_is_url(markup)

        rejections = []
        success = False
        for (self.markup, self.original_encoding, self.declared_html_encoding,
         self.contains_replacement_characters) in (
             self.builder.prepare_markup(
                 markup, from_encoding, exclude_encodings=exclude_encodings)):
            self.reset()
            try:
                self._feed()
                success = True
                break
            except ParserRejectedMarkup as e:
                rejections.append(e)
                pass

        if not success:
            other_exceptions = [str(e) for e in rejections]
            raise ParserRejectedMarkup(
                "The markup you provided was rejected by the parser. Trying a different parser or a different encoding may help.\n\nOriginal exception(s) from parser:\n " + "\n ".join(other_exceptions)
            )

        # Clear out the markup and remove the builder's circular
        # reference to this object.
        self.markup = None
        self.builder.soup = None

    def __copy__(self):
        """Copy a BeautifulSoup object by converting the document to a string and parsing it again."""
        copy = type(self)(
            self.encode('utf-8'), builder=self.builder, from_encoding='utf-8'
        )

        # Although we encoded the tree to UTF-8, that may not have
        # been the encoding of the original markup. Set the copy's
        # .original_encoding to reflect the original object's
        # .original_encoding.
        copy.original_encoding = self.original_encoding
        return copy

    def __getstate__(self):
        # Frequently a tree builder can't be pickled.
        d = dict(self.__dict__)
        if 'builder' in d and not self.builder.picklable:
            d['builder'] = None
        return d

    @classmethod
    def _decode_markup(cls, markup):
        """Ensure `markup` is bytes so it's safe to send into warnings.warn.

        TODO: warnings.warn had this problem back in 2010 but it might not
        anymore.
        """
        if isinstance(markup, bytes):
            decoded = markup.decode('utf-8', 'replace')
        else:
            decoded = markup
        return decoded

    @classmethod
    def _check_markup_is_url(cls, markup):
        """Error-handling method to raise a warning if incoming markup looks
        like a URL.

        :param markup: A string.
        """
        if isinstance(markup, bytes):
            space = b' '
            cant_start_with = (b"http:", b"https:")
        elif isinstance(markup, str):
            space = ' '
            cant_start_with = ("http:", "https:")
        else:
            return

        if any(markup.startswith(prefix) for prefix in cant_start_with):
            if not space in markup:
                warnings.warn(
                    '"%s" looks like a URL. Beautiful Soup is not an'
                    ' HTTP client. You should probably use an HTTP client like'
                    ' requests to get the document behind the URL, and feed'
                    ' that document to Beautiful Soup.' % cls._decode_markup(
                        markup
                    ),
                    MarkupResemblesLocatorWarning
                )

    def _feed(self):
        """Internal method that parses previously set markup, creating a large
        number of Tag and NavigableString objects.
        """
        # Convert the document to Unicode.
        self.builder.reset()

        self.builder.feed(self.markup)
        # Close out any unfinished strings and close all the open tags.
        self.endData()
        while self.currentTag.name != self.ROOT_TAG_NAME:
            self.popTag()

    def reset(self):
        """Reset this object to a state as though it had never parsed any
        markup.
        """
        Tag.__init__(self, self, self.builder, self.ROOT_TAG_NAME)
        self.hidden = 1
        self.builder.reset()
        self.current_data = []
        self.currentTag = None
        self.tagStack = []
        self.preserve_whitespace_tag_stack = []
        self.string_container_stack = []
        self.pushTag(self)

    def new_tag(self, name, namespace=None, nsprefix=None, attrs={},
                sourceline=None, sourcepos=None, **kwattrs):
        """Create a new Tag associated with this BeautifulSoup object.

        :param name: The name of the new Tag.
        :param namespace: The URI of the new Tag's XML namespace, if any.
        :param prefix: The prefix for the new Tag's XML namespace, if any.
        :param attrs: A dictionary of this Tag's attribute values; can
            be used instead of `kwattrs` for attributes like 'class'
            that are reserved words in Python.
        :param sourceline: The line number where this tag was
            (purportedly) found in its source document.
        :param sourcepos: The character position within `sourceline` where this
            tag was (purportedly) found.
        :param kwattrs: Keyword arguments for the new Tag's attribute values.

        """
        kwattrs.update(attrs)
        return self.element_classes.get(Tag, Tag)(
            None, self.builder, name, namespace, nsprefix, kwattrs,
            sourceline=sourceline, sourcepos=sourcepos
        )

    def string_container(self, base_class=None):
        container = base_class or NavigableString
        
        # There may be a general override of NavigableString.
        container = self.element_classes.get(
            container, container
        )

        # On top of that, we may be inside a tag that needs a special
        # container class.
        if self.string_container_stack:
            container = self.builder.string_containers.get(
                self.string_container_stack[-1].name, container
            )
        return container
        
    def new_string(self, s, subclass=None):
        """Create a new NavigableString associated with this BeautifulSoup
        object.
        """
        container = self.string_container(subclass)
        return container(s)

    def insert_before(self, successor):
        """This method is part of the PageElement API, but `BeautifulSoup` doesn't implement
        it because there is nothing before or after it in the parse tree.
        """
        raise NotImplementedError("BeautifulSoup objects don't support insert_before().")

    def insert_after(self, successor):
        """This method is part of the PageElement API, but `BeautifulSoup` doesn't implement
        it because there is nothing before or after it in the parse tree.
        """
        raise NotImplementedError("BeautifulSoup objects don't support insert_after().")

    def popTag(self):
        """Internal method called by _popToTag when a tag is closed."""
        tag = self.tagStack.pop()
        if self.preserve_whitespace_tag_stack and tag == self.preserve_whitespace_tag_stack[-1]:
            self.preserve_whitespace_tag_stack.pop()
        if self.string_container_stack and tag == self.string_container_stack[-1]:
            self.string_container_stack.pop()
        #print("Pop", tag.name)
        if self.tagStack:
            self.currentTag = self.tagStack[-1]
        return self.currentTag

    def pushTag(self, tag):
        """Internal method called by handle_starttag when a tag is opened."""
        #print("Push", tag.name)
        if self.currentTag is not None:
            self.currentTag.contents.append(tag)
        self.tagStack.append(tag)
        self.currentTag = self.tagStack[-1]
        if tag.name in self.builder.preserve_whitespace_tags:
            self.preserve_whitespace_tag_stack.append(tag)
        if tag.name in self.builder.string_containers:
            self.string_container_stack.append(tag)

    def endData(self, containerClass=None):
        """Method called by the TreeBuilder when the end of a data segment
        occurs.
        """
        containerClass = self.string_container(containerClass)
        
        if self.current_data:
            current_data = ''.join(self.current_data)
            # If whitespace is not preserved, and this string contains
            # nothing but ASCII spaces, replace it with a single space
            # or newline.
            if not self.preserve_whitespace_tag_stack:
                strippable = True
                for i in current_data:
                    if i not in self.ASCII_SPACES:
                        strippable = False
                        break
                if strippable:
                    if '\n' in current_data:
                        current_data = '\n'
                    else:
                        current_data = ' '

            # Reset the data collector.
            self.current_data = []

            # Should we add this string to the tree at all?
            if self.parse_only and len(self.tagStack) <= 1 and \
                   (not self.parse_only.text or \
                    not self.parse_only.search(current_data)):
                return

            o = containerClass(current_data)
            self.object_was_parsed(o)

    def object_was_parsed(self, o, parent=None, most_recent_element=None):
        """Method called by the TreeBuilder to integrate an object into the parse tree."""
        if parent is None:
            parent = self.currentTag
        if most_recent_element is not None:
            previous_element = most_recent_element
        else:
            previous_element = self._most_recent_element

        next_element = previous_sibling = next_sibling = None
        if isinstance(o, Tag):
            next_element = o.next_element
            next_sibling = o.next_sibling
            previous_sibling = o.previous_sibling
            if previous_element is None:
                previous_element = o.previous_element

        fix = parent.next_element is not None

        o.setup(parent, previous_element, next_element, previous_sibling, next_sibling)

        self._most_recent_element = o
        parent.contents.append(o)

        # Check if we are inserting into an already parsed node.
        if fix:
            self._linkage_fixer(parent)

    def _linkage_fixer(self, el):
        """Make sure linkage of this fragment is sound."""

        first = el.contents[0]
        child = el.contents[-1]
        descendant = child

        if child is first and el.parent is not None:
            # Parent should be linked to first child
            el.next_element = child
            # We are no longer linked to whatever this element is
            prev_el = child.previous_element
            if prev_el is not None and prev_el is not el:
                prev_el.next_element = None
            # First child should be linked to the parent, and no previous siblings.
            child.previous_element = el
            child.previous_sibling = None

        # We have no sibling as we've been appended as the last.
        child.next_sibling = None

        # This index is a tag, dig deeper for a "last descendant"
        if isinstance(child, Tag) and child.contents:
            descendant = child._last_descendant(False)

        # As the final step, link last descendant. It should be linked
        # to the parent's next sibling (if found), else walk up the chain
        # and find a parent with a sibling. It should have no next sibling.
        descendant.next_element = None
        descendant.next_sibling = None
        target = el
        while True:
            if target is None:
                break
            elif target.next_sibling is not None:
                descendant.next_element = target.next_sibling
                target.next_sibling.previous_element = child
                break
            target = target.parent

    def _popToTag(self, name, nsprefix=None, inclusivePop=True):
        """Pops the tag stack up to and including the most recent
        instance of the given tag. 

        :param name: Pop up to the most recent tag with this name.
        :param nsprefix: The namespace prefix that goes with `name`.
        :param inclusivePop: It this is false, pops the tag stack up
          to but *not* including the most recent instqance of the
          given tag.
        """
        #print("Popping to %s" % name)
        if name == self.ROOT_TAG_NAME:
            # The BeautifulSoup object itself can never be popped.
            return

        most_recently_popped = None

        stack_size = len(self.tagStack)
        for i in range(stack_size - 1, 0, -1):
            t = self.tagStack[i]
            if (name == t.name and nsprefix == t.prefix):
                if inclusivePop:
                    most_recently_popped = self.popTag()
                break
            most_recently_popped = self.popTag()

        return most_recently_popped

    def handle_starttag(self, name, namespace, nsprefix, attrs, sourceline=None,
                        sourcepos=None):
        """Called by the tree builder when a new tag is encountered.

        :param name: Name of the tag.
        :param nsprefix: Namespace prefix for the tag.
        :param attrs: A dictionary of attribute values.
        :param sourceline: The line number where this tag was found in its
            source document.
        :param sourcepos: The character position within `sourceline` where this
            tag was found.

        If this method returns None, the tag was rejected by an active
        SoupStrainer. You should proceed as if the tag had not occurred
        in the document. For instance, if this was a self-closing tag,
        don't call handle_endtag.
        """
        # print("Start tag %s: %s" % (name, attrs))
        self.endData()

        if (self.parse_only and len(self.tagStack) <= 1
            and (self.parse_only.text
                 or not self.parse_only.search_tag(name, attrs))):
            return None

        tag = self.element_classes.get(Tag, Tag)(
            self, self.builder, name, namespace, nsprefix, attrs,
            self.currentTag, self._most_recent_element,
            sourceline=sourceline, sourcepos=sourcepos
        )
        if tag is None:
            return tag
        if self._most_recent_element is not None:
            self._most_recent_element.next_element = tag
        self._most_recent_element = tag
        self.pushTag(tag)
        return tag

    def handle_endtag(self, name, nsprefix=None):
        """Called by the tree builder when an ending tag is encountered.

        :param name: Name of the tag.
        :param nsprefix: Namespace prefix for the tag.
        """
        #print("End tag: " + name)
        self.endData()
        self._popToTag(name, nsprefix)

    def handle_data(self, data):
        """Called by the tree builder when a chunk of textual data is encountered."""
        self.current_data.append(data)
       
    def decode(self, pretty_print=False,
               eventual_encoding=DEFAULT_OUTPUT_ENCODING,
               formatter="minimal"):
        """Returns a string or Unicode representation of the parse tree
            as an HTML or XML document.

        :param pretty_print: If this is True, indentation will be used to
            make the document more readable.
        :param eventual_encoding: The encoding of the final document.
            If this is None, the document will be a Unicode string.
        """
        if self.is_xml:
            # Print the XML declaration
            encoding_part = ''
            if eventual_encoding in PYTHON_SPECIFIC_ENCODINGS:
                # This is a special Python encoding; it can't actually
                # go into an XML document because it means nothing
                # outside of Python.
                eventual_encoding = None
            if eventual_encoding != None:
                encoding_part = ' encoding="%s"' % eventual_encoding
            prefix = '<?xml version="1.0"%s?>\n' % encoding_part
        else:
            prefix = ''
        if not pretty_print:
            indent_level = None
        else:
            indent_level = 0
        return prefix + super(BeautifulSoup, self).decode(
            indent_level, eventual_encoding, formatter)

# Aliases to make it easier to get started quickly, e.g. 'from bs4 import _soup'
_s = BeautifulSoup
_soup = BeautifulSoup

class BeautifulStoneSoup(BeautifulSoup):
    """Deprecated interface to an XML parser."""

    def __init__(self, *args, **kwargs):
        kwargs['features'] = 'xml'
        warnings.warn(
            'The BeautifulStoneSoup class is deprecated. Instead of using '
            'it, pass features="xml" into the BeautifulSoup constructor.')
        super(BeautifulStoneSoup, self).__init__(*args, **kwargs)


class StopParsing(Exception):
    """Exception raised by a TreeBuilder if it's unable to continue parsing."""
    pass

class FeatureNotFound(ValueError):
    """Exception raised by the BeautifulSoup constructor if no parser with the
    requested features is found.
    """
    pass


#If this file is run as a script, act as an HTML pretty-printer.
if __name__ == '__main__':
    import sys
    soup = BeautifulSoup(sys.stdin)
    print((soup.prettify()))