Source code for astropy.utils.xml.writer

# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
Contains a class that makes it simple to stream out well-formed and
nicely-indented XML.
"""

# STDLIB
import contextlib
import textwrap

try:
    from . import _iterparser
except ImportError:
    def xml_escape_cdata(s):
        """
        Escapes &, < and > in an XML CDATA string.
        """
        s = s.replace("&", "&amp;")
        s = s.replace("<", "&lt;")
        s = s.replace(">", "&gt;")
        return s

    def xml_escape(s):
        """
        Escapes &, ', ", < and > in an XML attribute value.
        """
        s = s.replace("&", "&amp;")
        s = s.replace("'", "&apos;")
        s = s.replace("\"", "&quot;")
        s = s.replace("<", "&lt;")
        s = s.replace(">", "&gt;")
        return s
else:
    xml_escape_cdata = _iterparser.escape_xml_cdata
    xml_escape = _iterparser.escape_xml


[docs]class XMLWriter: """ A class to write well-formed and nicely indented XML. Use like this:: w = XMLWriter(fh) with w.tag('html'): with w.tag('body'): w.data('This is the content') Which produces:: <html> <body> This is the content </body> </html> """ def __init__(self, file): """ Parameters ---------- file : writable file-like object. """ self.write = file.write if hasattr(file, "flush"): self.flush = file.flush self._open = 0 # true if start tag is open self._tags = [] self._data = [] self._indentation = " " * 64 self.xml_escape_cdata = xml_escape_cdata self.xml_escape = xml_escape def _flush(self, indent=True, wrap=False): """ Flush internal buffers. """ if self._open: if indent: self.write(">\n") else: self.write(">") self._open = 0 if self._data: data = ''.join(self._data) if wrap: indent = self.get_indentation_spaces(1) data = textwrap.fill( data, initial_indent=indent, subsequent_indent=indent) self.write('\n') self.write(self.xml_escape_cdata(data)) self.write('\n') self.write(self.get_indentation_spaces()) else: self.write(self.xml_escape_cdata(data)) self._data = []
[docs] def start(self, tag, attrib={}, **extra): """ Opens a new element. Attributes can be given as keyword arguments, or as a string/string dictionary. The method returns an opaque identifier that can be passed to the :meth:`close` method, to close all open elements up to and including this one. Parameters ---------- tag : str The element name attrib : dict of str -> str Attribute dictionary. Alternatively, attributes can be given as keyword arguments. Returns ------- id : int Returns an element identifier. """ self._flush() # This is just busy work -- we know our tag names are clean # tag = xml_escape_cdata(tag) self._data = [] self._tags.append(tag) self.write(self.get_indentation_spaces(-1)) self.write(f"<{tag}") if attrib or extra: attrib = attrib.copy() attrib.update(extra) attrib = list(attrib.items()) attrib.sort() for k, v in attrib: if v is not None: # This is just busy work -- we know our keys are clean # k = xml_escape_cdata(k) v = self.xml_escape(v) self.write(f" {k}=\"{v}\"") self._open = 1 return len(self._tags)
[docs] @contextlib.contextmanager def xml_cleaning_method(self, method='escape_xml', **clean_kwargs): """Context manager to control how XML data tags are cleaned (escaped) to remove potentially unsafe characters or constructs. The default (``method='escape_xml'``) applies brute-force escaping of certain key XML characters like ``<``, ``>``, and ``&`` to ensure that the output is not valid XML. In order to explicitly allow certain XML tags (e.g. link reference or emphasis tags), use ``method='bleach_clean'``. This sanitizes the data string using the ``clean`` function of the `https://bleach.readthedocs.io/en/latest/clean.html <bleach>`_ package. Any additional keyword arguments will be passed directly to the ``clean`` function. Finally, use ``method='none'`` to disable any sanitization. This should be used sparingly. Example:: w = writer.XMLWriter(ListWriter(lines)) with w.xml_cleaning_method('bleach_clean'): w.start('td') w.data('<a href="https://google.com">google.com</a>') w.end() Parameters ---------- method : str Cleaning method. Allowed values are "escape_xml", "bleach_clean", and "none". **clean_kwargs : keyword args Additional keyword args that are passed to the bleach.clean() function. """ current_xml_escape_cdata = self.xml_escape_cdata if method == 'bleach_clean': # NOTE: bleach is imported locally to avoid importing it when # it is not nocessary try: import bleach except ImportError: raise ValueError('bleach package is required when HTML escaping is disabled.\n' 'Use "pip install bleach".') if clean_kwargs is None: clean_kwargs = {} self.xml_escape_cdata = lambda x: bleach.clean(x, **clean_kwargs) elif method == "none": self.xml_escape_cdata = lambda x: x elif method != 'escape_xml': raise ValueError('allowed values of method are "escape_xml", "bleach_clean", and "none"') yield self.xml_escape_cdata = current_xml_escape_cdata
[docs] @contextlib.contextmanager def tag(self, tag, attrib={}, **extra): """ A convenience method for creating wrapper elements using the ``with`` statement. Examples -------- >>> with writer.tag('foo'): # doctest: +SKIP ... writer.element('bar') ... # </foo> is implicitly closed here ... Parameters are the same as to `start`. """ self.start(tag, attrib, **extra) yield self.end(tag)
[docs] def comment(self, comment): """ Adds a comment to the output stream. Parameters ---------- comment : str Comment text, as a Unicode string. """ self._flush() self.write(self.get_indentation_spaces()) self.write("<!-- {} -->\n".format(self.xml_escape_cdata(comment)))
[docs] def data(self, text): """ Adds character data to the output stream. Parameters ---------- text : str Character data, as a Unicode string. """ self._data.append(text)
[docs] def end(self, tag=None, indent=True, wrap=False): """ Closes the current element (opened by the most recent call to `start`). Parameters ---------- tag : str Element name. If given, the tag must match the start tag. If omitted, the current element is closed. """ if tag: if not self._tags: raise ValueError(f"unbalanced end({tag})") if tag != self._tags[-1]: raise ValueError("expected end({}), got {}".format( self._tags[-1], tag)) else: if not self._tags: raise ValueError("unbalanced end()") tag = self._tags.pop() if self._data: self._flush(indent, wrap) elif self._open: self._open = 0 self.write("/>\n") return if indent: self.write(self.get_indentation_spaces()) self.write(f"</{tag}>\n")
[docs] def close(self, id): """ Closes open elements, up to (and including) the element identified by the given identifier. Parameters ---------- id : int Element identifier, as returned by the `start` method. """ while len(self._tags) > id: self.end()
[docs] def element(self, tag, text=None, wrap=False, attrib={}, **extra): """ Adds an entire element. This is the same as calling `start`, `data`, and `end` in sequence. The ``text`` argument can be omitted. """ self.start(tag, attrib, **extra) if text: self.data(text) self.end(indent=False, wrap=wrap)
[docs] def flush(self): pass # replaced by the constructor
[docs] def get_indentation(self): """ Returns the number of indentation levels the file is currently in. """ return len(self._tags)
[docs] def get_indentation_spaces(self, offset=0): """ Returns a string of spaces that matches the current indentation level. """ return self._indentation[:len(self._tags) + offset]
[docs] @staticmethod def object_attrs(obj, attrs): """ Converts an object with a bunch of attributes on an object into a dictionary for use by the `XMLWriter`. Parameters ---------- obj : object Any Python object attrs : sequence of str Attribute names to pull from the object Returns ------- attrs : dict Maps attribute names to the values retrieved from ``obj.attr``. If any of the attributes is `None`, it will not appear in the output dictionary. """ d = {} for attr in attrs: if getattr(obj, attr) is not None: d[attr.replace('_', '-')] = str(getattr(obj, attr)) return d