~bzr-pqm/bzr/bzr.dev

#

# ElementTree

# $Id: ElementTree.py 2326 2005-03-17 07:45:21Z fredrik $

#

# light-weight XML support for Python 1.5.2 and later.

#

# history:

# 2001-10-20 fl   created (from various sources)

# 2001-11-01 fl   return root from parse method

# 2002-02-16 fl   sort attributes in lexical order

# 2002-04-06 fl   TreeBuilder refactoring, added PythonDoc markup

# 2002-05-01 fl   finished TreeBuilder refactoring

# 2002-07-14 fl   added basic namespace support to ElementTree.write

# 2002-07-25 fl   added QName attribute support

# 2002-10-20 fl   fixed encoding in write

# 2002-11-24 fl   changed default encoding to ascii; fixed attribute encoding

# 2002-11-27 fl   accept file objects or file names for parse/write

# 2002-12-04 fl   moved XMLTreeBuilder back to this module

# 2003-01-11 fl   fixed entity encoding glitch for us-ascii

# 2003-02-13 fl   added XML literal factory

# 2003-02-21 fl   added ProcessingInstruction/PI factory

# 2003-05-11 fl   added tostring/fromstring helpers

# 2003-05-26 fl   added ElementPath support

# 2003-07-05 fl   added makeelement factory method

# 2003-07-28 fl   added more well-known namespace prefixes

# 2003-08-15 fl   fixed typo in ElementTree.findtext (Thomas Dartsch)

# 2003-09-04 fl   fall back on emulator if ElementPath is not installed

# 2003-10-31 fl   markup updates

# 2003-11-15 fl   fixed nested namespace bug

# 2004-03-28 fl   added XMLID helper

# 2004-06-02 fl   added default support to findtext

# 2004-06-08 fl   fixed encoding of non-ascii element/attribute names

# 2004-08-23 fl   take advantage of post-2.1 expat features

# 2005-02-01 fl   added iterparse implementation

# 2005-03-02 fl   fixed iterparse support for pre-2.2 versions

#

# Copyright (c) 1999-2005 by Fredrik Lundh.  All rights reserved.

#

# fredrik@pythonware.com

# http://www.pythonware.com

#

# --------------------------------------------------------------------

# The ElementTree toolkit is

#

# Copyright (c) 1999-2005 by Fredrik Lundh

#

# By obtaining, using, and/or copying this software and/or its

# associated documentation, you agree that you have read, understood,

# and will comply with the following terms and conditions:

#

# Permission to use, copy, modify, and distribute this software and

# its associated documentation for any purpose and without fee is

# hereby granted, provided that the above copyright notice appears in

# all copies, and that both that copyright notice and this permission

# notice appear in supporting documentation, and that the name of

# Secret Labs AB or the author not be used in advertising or publicity

# pertaining to distribution of the software without specific, written

# prior permission.

#

# SECRET LABS AB AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD

# TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANT-

# ABILITY AND FITNESS.  IN NO EVENT SHALL SECRET LABS AB OR THE AUTHOR

# BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY

# DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,

# WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS

# ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE

# OF THIS SOFTWARE.

# --------------------------------------------------------------------

__all__ = [

    # public symbols

    "Comment",

    "dump",

    "Element", "ElementTree",

    "fromstring",

    "iselement", "iterparse",

    "parse",

    "PI", "ProcessingInstruction",

    "QName",

    "SubElement",

    "tostring",

    "TreeBuilder",

    "VERSION", "XML",

    "XMLTreeBuilder",

    ]

##

# The <b>Element</b> type is a flexible container object, designed to

# store hierarchical data structures in memory. The type can be

# described as a cross between a list and a dictionary.

# <p>

# Each element has a number of properties associated with it:

# <ul>

# <li>a <i>tag</i>. This is a string identifying what kind of data

# this element represents (the element type, in other words).</li>

# <li>a number of <i>attributes</i>, stored in a Python dictionary.</li>

# <li>a <i>text</i> string.</li>

# <li>an optional <i>tail</i> string.</li>

# <li>a number of <i>child elements</i>, stored in a Python sequence</li>

# </ul>

#

# To create an element instance, use the {@link #Element} or {@link

# #SubElement} factory functions.

# <p>

# The {@link #ElementTree} class can be used to wrap an element

# structure, and convert it from and to XML.

##

import string, sys, re

class _SimpleElementPath:

    # emulate pre-1.2 find/findtext/findall behaviour

    def find(self, element, tag):

        for elem in element:

            if elem.tag == tag:

                return elem

        return None

    def findtext(self, element, tag, default=None):

        for elem in element:

            if elem.tag == tag:

                return elem.text or ""

        return default

    def findall(self, element, tag):

        if tag[:3] == ".//":

            return element.getiterator(tag[3:])

        result = []

        for elem in element:

            if elem.tag == tag:

                result.append(elem)

        return result

try:

    import ElementPath

except ImportError:

    # FIXME: issue warning in this case?

    ElementPath = _SimpleElementPath()

# TODO: add support for custom namespace resolvers/default namespaces

# TODO: add improved support for incremental parsing

VERSION = "1.2.6"

##

# Internal element class.  This class defines the Element interface,

# and provides a reference implementation of this interface.

# <p>

# You should not create instances of this class directly.  Use the

# appropriate factory functions instead, such as {@link #Element}

# and {@link #SubElement}.

#

# @see Element

# @see SubElement

# @see Comment

# @see ProcessingInstruction

class _ElementInterface:

    # <tag attrib>text<child/>...</tag>tail

    ##

    # (Attribute) Element tag.

    tag = None

    ##

    # (Attribute) Element attribute dictionary.  Where possible, use

    # {@link #_ElementInterface.get},

    # {@link #_ElementInterface.set},

    # {@link #_ElementInterface.keys}, and

    # {@link #_ElementInterface.items} to access

    # element attributes.

    attrib = None

    ##

    # (Attribute) Text before first subelement.  This is either a

    # string or the value None, if there was no text.

    text = None

    ##

    # (Attribute) Text after this element's end tag, but before the

    # next sibling element's start tag.  This is either a string or

    # the value None, if there was no text.

    tail = None # text after end tag, if any

    def __init__(self, tag, attrib):

        self.tag = tag

        self.attrib = attrib

        self._children = []

    def __repr__(self):

        return "<Element %s at %x>" % (self.tag, id(self))

    ##

    # Creates a new element object of the same type as this element.

    #

    # @param tag Element tag.

    # @param attrib Element attributes, given as a dictionary.

    # @return A new element instance.

    def makeelement(self, tag, attrib):

        return Element(tag, attrib)

    ##

    # Returns the number of subelements.

    #

    # @return The number of subelements.

    def __len__(self):

        return len(self._children)

    ##

    # Returns the given subelement.

    #

    # @param index What subelement to return.

    # @return The given subelement.

    # @exception IndexError If the given element does not exist.

    def __getitem__(self, index):

        return self._children[index]

    ##

    # Replaces the given subelement.

    #

    # @param index What subelement to replace.

    # @param element The new element value.

    # @exception IndexError If the given element does not exist.

    # @exception AssertionError If element is not a valid object.

    def __setitem__(self, index, element):

        assert iselement(element)

        self._children[index] = element

    ##

    # Deletes the given subelement.

    #

    # @param index What subelement to delete.

    # @exception IndexError If the given element does not exist.

    def __delitem__(self, index):

        del self._children[index]

    ##

    # Returns a list containing subelements in the given range.

    #

    # @param start The first subelement to return.

    # @param stop The first subelement that shouldn't be returned.

    # @return A sequence object containing subelements.

    def __getslice__(self, start, stop):

        return self._children[start:stop]

    ##

    # Replaces a number of subelements with elements from a sequence.

    #

    # @param start The first subelement to replace.

    # @param stop The first subelement that shouldn't be replaced.

    # @param elements A sequence object with zero or more elements.

    # @exception AssertionError If a sequence member is not a valid object.

    def __setslice__(self, start, stop, elements):

        for element in elements:

            assert iselement(element)

        self._children[start:stop] = list(elements)

    ##

    # Deletes a number of subelements.

    #

    # @param start The first subelement to delete.

    # @param stop The first subelement to leave in there.

    def __delslice__(self, start, stop):

        del self._children[start:stop]

    ##

    # Adds a subelement to the end of this element.

    #

    # @param element The element to add.

    # @exception AssertionError If a sequence member is not a valid object.

    def append(self, element):

        assert iselement(element)

        self._children.append(element)

    ##

    # Inserts a subelement at the given position in this element.

    #

    # @param index Where to insert the new subelement.

    # @exception AssertionError If the element is not a valid object.

    def insert(self, index, element):

        assert iselement(element)

        self._children.insert(index, element)

    ##

    # Removes a matching subelement.  Unlike the <b>find</b> methods,

    # this method compares elements based on identity, not on tag

    # value or contents.

    #

    # @param element What element to remove.

    # @exception ValueError If a matching element could not be found.

    # @exception AssertionError If the element is not a valid object.

    def remove(self, element):

        assert iselement(element)

        self._children.remove(element)

    ##

    # Returns all subelements.  The elements are returned in document

    # order.

    #

    # @return A list of subelements.

    # @defreturn list of Element instances

    def getchildren(self):

        return self._children

    ##

    # Finds the first matching subelement, by tag name or path.

    #

    # @param path What element to look for.

    # @return The first matching element, or None if no element was found.

    # @defreturn Element or None

    def find(self, path):

        return ElementPath.find(self, path)

    ##

    # Finds text for the first matching subelement, by tag name or path.

    #

    # @param path What element to look for.

    # @param default What to return if the element was not found.

    # @return The text content of the first matching element, or the

    #     default value no element was found.  Note that if the element

    #     has is found, but has no text content, this method returns an

    #     empty string.

    # @defreturn string

    def findtext(self, path, default=None):

        return ElementPath.findtext(self, path, default)

    ##

    # Finds all matching subelements, by tag name or path.

    #

    # @param path What element to look for.

    # @return A list or iterator containing all matching elements,

    #    in document order.

    # @defreturn list of Element instances

    def findall(self, path):

        return ElementPath.findall(self, path)

    ##

    # Resets an element.  This function removes all subelements, clears

    # all attributes, and sets the text and tail attributes to None.

    def clear(self):

        self.attrib.clear()

        self._children = []

        self.text = self.tail = None

    ##

    # Gets an element attribute.

    #

    # @param key What attribute to look for.

    # @param default What to return if the attribute was not found.

    # @return The attribute value, or the default value, if the

    #     attribute was not found.

    # @defreturn string or None

    def get(self, key, default=None):

        return self.attrib.get(key, default)

    ##

    # Sets an element attribute.

    #

    # @param key What attribute to set.

    # @param value The attribute value.

    def set(self, key, value):

        self.attrib[key] = value

    ##

    # Gets a list of attribute names.  The names are returned in an

    # arbitrary order (just like for an ordinary Python dictionary).

    #

    # @return A list of element attribute names.

    # @defreturn list of strings

    def keys(self):

        return self.attrib.keys()

    ##

    # Gets element attributes, as a sequence.  The attributes are

    # returned in an arbitrary order.

    #

    # @return A list of (name, value) tuples for all attributes.

    # @defreturn list of (string, string) tuples

    def items(self):

        return self.attrib.items()

    ##

    # Creates a tree iterator.  The iterator loops over this element

    # and all subelements, in document order, and returns all elements

    # with a matching tag.

    # <p>

    # If the tree structure is modified during iteration, the result

    # is undefined.

    #

    # @param tag What tags to look for (default is to return all elements).

    # @return A list or iterator containing all the matching elements.

    # @defreturn list or iterator

    def getiterator(self, tag=None):

        nodes = []

        if tag == "*":

            tag = None

        if tag is None or self.tag == tag:

            nodes.append(self)

        for node in self._children:

            nodes.extend(node.getiterator(tag))

        return nodes

# compatibility

_Element = _ElementInterface

##

# Element factory.  This function returns an object implementing the

# standard Element interface.  The exact class or type of that object

# is implementation dependent, but it will always be compatible with

# the {@link #_ElementInterface} class in this module.

# <p>

# The element name, attribute names, and attribute values can be

# either 8-bit ASCII strings or Unicode strings.

#

# @param tag The element name.

# @param attrib An optional dictionary, containing element attributes.

# @param **extra Additional attributes, given as keyword arguments.

# @return An element instance.

# @defreturn Element

def Element(tag, attrib={}, **extra):

    attrib = attrib.copy()

    attrib.update(extra)

    return _ElementInterface(tag, attrib)

##

# Subelement factory.  This function creates an element instance, and

# appends it to an existing element.

# <p>

# The element name, attribute names, and attribute values can be

# either 8-bit ASCII strings or Unicode strings.

#

# @param parent The parent element.

# @param tag The subelement name.

# @param attrib An optional dictionary, containing element attributes.

# @param **extra Additional attributes, given as keyword arguments.

# @return An element instance.

# @defreturn Element

def SubElement(parent, tag, attrib={}, **extra):

    attrib = attrib.copy()

    attrib.update(extra)

    element = parent.makeelement(tag, attrib)

    parent.append(element)

    return element

##

# Comment element factory.  This factory function creates a special

# element that will be serialized as an XML comment.

# <p>

# The comment string can be either an 8-bit ASCII string or a Unicode

# string.

#

# @param text A string containing the comment string.

# @return An element instance, representing a comment.

# @defreturn Element

def Comment(text=None):

    element = Element(Comment)

    element.text = text

    return element

##

# PI element factory.  This factory function creates a special element

# that will be serialized as an XML processing instruction.

#

# @param target A string containing the PI target.

# @param text A string containing the PI contents, if any.

# @return An element instance, representing a PI.

# @defreturn Element

def ProcessingInstruction(target, text=None):

    element = Element(ProcessingInstruction)

    element.text = target

    if text:

        element.text = element.text + " " + text

    return element

PI = ProcessingInstruction

##

# QName wrapper.  This can be used to wrap a QName attribute value, in

# order to get proper namespace handling on output.

#

# @param text A string containing the QName value, in the form {uri}local,

#     or, if the tag argument is given, the URI part of a QName.

# @param tag Optional tag.  If given, the first argument is interpreted as

#     an URI, and this argument is interpreted as a local name.

# @return An opaque object, representing the QName.

class QName:

    def __init__(self, text_or_uri, tag=None):

        if tag:

            text_or_uri = "{%s}%s" % (text_or_uri, tag)

        self.text = text_or_uri

    def __str__(self):

        return self.text

    def __hash__(self):

        return hash(self.text)

    def __cmp__(self, other):

        if isinstance(other, QName):

            return cmp(self.text, other.text)

        return cmp(self.text, other)

##

# ElementTree wrapper class.  This class represents an entire element

# hierarchy, and adds some extra support for serialization to and from

# standard XML.

#

# @param element Optional root element.

# @keyparam file Optional file handle or name.  If given, the

#     tree is initialized with the contents of this XML file.

class ElementTree:

    def __init__(self, element=None, file=None):

        assert element is None or iselement(element)

        self._root = element # first node

        if file:

            self.parse(file)

    ##

    # Gets the root element for this tree.

    #

    # @return An element instance.

    # @defreturn Element

    def getroot(self):

        return self._root

    ##

    # Replaces the root element for this tree.  This discards the

    # current contents of the tree, and replaces it with the given

    # element.  Use with care.

    #

    # @param element An element instance.

    def _setroot(self, element):

        assert iselement(element)

        self._root = element

    ##

    # Loads an external XML document into this element tree.

    #

    # @param source A file name or file object.

    # @param parser An optional parser instance.  If not given, the

    #     standard {@link XMLTreeBuilder} parser is used.

    # @return The document root element.

    # @defreturn Element

    def parse(self, source, parser=None):

        if getattr(source, "read", None) is None:

            source = open(source, "rb")

        if not parser:

            parser = XMLTreeBuilder()

        while 1:

            data = source.read(32768)

            if not data:

                break

            parser.feed(data)

        self._root = parser.close()

        return self._root

    ##

    # Creates a tree iterator for the root element.  The iterator loops

    # over all elements in this tree, in document order.

    #

    # @param tag What tags to look for (default is to return all elements)

    # @return An iterator.

    # @defreturn iterator

    def getiterator(self, tag=None):

        assert self._root is not None

        return self._root.getiterator(tag)

    ##

    # Finds the first toplevel element with given tag.

    # Same as getroot().find(path).

    #

    # @param path What element to look for.

    # @return The first matching element, or None if no element was found.

    # @defreturn Element or None

    def find(self, path):

        assert self._root is not None

        if path[:1] == "/":

            path = "." + path

        return self._root.find(path)

    ##

    # Finds the element text for the first toplevel element with given

    # tag.  Same as getroot().findtext(path).

    #

    # @param path What toplevel element to look for.

    # @param default What to return if the element was not found.

    # @return The text content of the first matching element, or the

    #     default value no element was found.  Note that if the element

    #     has is found, but has no text content, this method returns an

    #     empty string.

    # @defreturn string

    def findtext(self, path, default=None):

        assert self._root is not None

        if path[:1] == "/":

            path = "." + path

        return self._root.findtext(path, default)

    ##

    # Finds all toplevel elements with the given tag.

    # Same as getroot().findall(path).

    #

    # @param path What element to look for.

    # @return A list or iterator containing all matching elements,

    #    in document order.

    # @defreturn list of Element instances

    def findall(self, path):

        assert self._root is not None

        if path[:1] == "/":

            path = "." + path

        return self._root.findall(path)

    ##

    # Writes the element tree to a file, as XML.

    #

    # @param file A file name, or a file object opened for writing.

    # @param encoding Optional output encoding (default is US-ASCII).

    def write(self, file, encoding="us-ascii"):

        assert self._root is not None

        if getattr(file, "write", None) is None:

            file = open(file, "wb")

        if not encoding:

            encoding = "us-ascii"

        elif encoding != "utf-8" and encoding != "us-ascii":

            file.write("<?xml version='1.0' encoding='%s'?>\n" % encoding)

        self._write(file, self._root, encoding, {})

    def _write(self, file, node, encoding, namespaces):

        # write XML to file

        tag = node.tag

        if tag is Comment:

            file.write("<!-- %s -->" % _escape_cdata(node.text, encoding))

        elif tag is ProcessingInstruction:

            file.write("<?%s?>" % _escape_cdata(node.text, encoding))

        else:

            items = node.items()

            xmlns_items = [] # new namespaces in this scope

            try:

                if isinstance(tag, QName) or tag[:1] == "{":

                    tag, xmlns = fixtag(tag, namespaces)

                    if xmlns: xmlns_items.append(xmlns)

            except TypeError:

                _raise_serialization_error(tag)

            file.write("<" + _encode(tag, encoding))

            if items or xmlns_items:

                items.sort() # lexical order

                for k, v in items:

                    try:

                        if isinstance(k, QName) or k[:1] == "{":

                            k, xmlns = fixtag(k, namespaces)

                            if xmlns: xmlns_items.append(xmlns)

                    except TypeError:

                        _raise_serialization_error(k)

                    try:

                        if isinstance(v, QName):

                            v, xmlns = fixtag(v, namespaces)

                            if xmlns: xmlns_items.append(xmlns)

                    except TypeError:

                        _raise_serialization_error(v)

                    file.write(" %s=\"%s\"" % (_encode(k, encoding),

                                               _escape_attrib(v, encoding)))

                for k, v in xmlns_items:

                    file.write(" %s=\"%s\"" % (_encode(k, encoding),

                                               _escape_attrib(v, encoding)))

            if node.text or len(node):

                file.write(">")

                if node.text:

                    file.write(_escape_cdata(node.text, encoding))

                for n in node:

                    self._write(file, n, encoding, namespaces)

                file.write("</" + _encode(tag, encoding) + ">")

            else:

                file.write(" />")

            for k, v in xmlns_items:

                del namespaces[v]

        if node.tail:

            file.write(_escape_cdata(node.tail, encoding))

# --------------------------------------------------------------------

# helpers

##

# Checks if an object appears to be a valid element object.

#

# @param An element instance.

# @return A true value if this is an element object.

# @defreturn flag

def iselement(element):

    # FIXME: not sure about this; might be a better idea to look

    # for tag/attrib/text attributes

    return isinstance(element, _ElementInterface) or (getattr(element, "tag", None) is not None)

##

# Writes an element tree or element structure to sys.stdout.  This

# function should be used for debugging only.

# <p>

# The exact output format is implementation dependent.  In this

# version, it's written as an ordinary XML file.

#

# @param elem An element tree or an individual element.

def dump(elem):

    # debugging

    if not isinstance(elem, ElementTree):

        elem = ElementTree(elem)

    elem.write(sys.stdout)

    tail = elem.getroot().tail

    if not tail or tail[-1] != "\n":

        sys.stdout.write("\n")

def _encode(s, encoding):

    try:

        return s.encode(encoding)

    except AttributeError:

        return s # 1.5.2: assume the string uses the right encoding

if sys.version[:3] == "1.5":

    _escape = re.compile(r"[&<>\"\x80-\xff]+") # 1.5.2

else:

    _escape = re.compile(eval(r'u"[&<>\"\u0080-\uffff]+"'))

_escape_map = {

    "&": "&",

    "<": "&lt;",

    ">": ">",

    '"': """,

}

_namespace_map = {

    # "well-known" namespace prefixes

    "http://www.w3.org/XML/1998/namespace": "xml",

    "http://www.w3.org/1999/xhtml": "html",

    "http://www.w3.org/1999/02/22-rdf-syntax-ns#": "rdf",

    "http://schemas.xmlsoap.org/wsdl/": "wsdl",

}

def _raise_serialization_error(text):

    raise TypeError(

        "cannot serialize %r (type %s)" % (text, type(text).__name__)

        )

def _encode_entity(text, pattern=_escape):

    # map reserved and non-ascii characters to numerical entities

    def escape_entities(m, map=_escape_map):

        out = []

        append = out.append

        for char in m.group():

            text = map.get(char)

            if text is None:

                text = "&#%d;" % ord(char)

            append(text)

        return string.join(out, "")

    try:

        return _encode(pattern.sub(escape_entities, text), "ascii")

    except TypeError:

        _raise_serialization_error(text)

#

# the following functions assume an ascii-compatible encoding

# (or "utf-16")

def _escape_cdata(text, encoding=None, replace=string.replace):

    # escape character data

    try:

        if encoding:

            try:

                text = _encode(text, encoding)

            except UnicodeError:

                return _encode_entity(text)

        text = replace(text, "&", "&")

        text = replace(text, "<", "&lt;")

        text = replace(text, ">", ">")

        return text

    except (TypeError, AttributeError):

        _raise_serialization_error(text)

def _escape_attrib(text, encoding=None, replace=string.replace):

    # escape attribute value

    try:

        if encoding:

            try:

                text = _encode(text, encoding)

            except UnicodeError:

                return _encode_entity(text)

        text = replace(text, "&", "&")

        text = replace(text, "'", "'") # FIXME: overkill

        text = replace(text, "\"", """)

        text = replace(text, "<", "&lt;")

        text = replace(text, ">", ">")

        return text

    except (TypeError, AttributeError):

        _raise_serialization_error(text)

def fixtag(tag, namespaces):

    # given a decorated tag (of the form {uri}tag), return prefixed

    # tag and namespace declaration, if any

    if isinstance(tag, QName):

        tag = tag.text

    namespace_uri, tag = string.split(tag[1:], "}", 1)

    prefix = namespaces.get(namespace_uri)

    if prefix is None:

        prefix = _namespace_map.get(namespace_uri)

        if prefix is None:

            prefix = "ns%d" % len(namespaces)

        namespaces[namespace_uri] = prefix

        if prefix == "xml":

            xmlns = None

        else:

            xmlns = ("xmlns:%s" % prefix, namespace_uri)

    else:

        xmlns = None

    return "%s:%s" % (prefix, tag), xmlns

##

# Parses an XML document into an element tree.

#

# @param source A filename or file object containing XML data.

# @param parser An optional parser instance.  If not given, the

#     standard {@link XMLTreeBuilder} parser is used.

# @return An ElementTree instance

def parse(source, parser=None):

    tree = ElementTree()

    tree.parse(source, parser)

    return tree

##

# Parses an XML document into an element tree incrementally, and reports

# what's going on to the user.

#

# @param source A filename or file object containing XML data.

# @param events A list of events to report back.  If omitted, only "end"

#     events are reported.

# @return A (event, elem) iterator.

class iterparse:

    def __init__(self, source, events=None):

        if getattr(source, "read", None) is None: