# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
This module includes a fast iterator-based XML parser.
"""
# STDLIB
import contextlib
import io
import sys
# ASTROPY
from astropy.utils import data
__all__ = ["get_xml_iterator", "get_xml_encoding", "xml_readlines"]
@contextlib.contextmanager
def _convert_to_fd_or_read_function(fd):
"""
Returns a function suitable for streaming input, or a file object.
This function is only useful if passing off to C code where:
- If it's a real file object, we want to use it as a real
C file object to avoid the Python overhead.
- If it's not a real file object, it's much handier to just
have a Python function to call.
This is somewhat quirky behavior, of course, which is why it is
private. For a more useful version of similar behavior, see
`astropy.utils.misc.get_readable_fileobj`.
Parameters
----------
fd : object
May be:
- a file object. If the file is uncompressed, this raw
file object is returned verbatim. Otherwise, the read
method is returned.
- a function that reads from a stream, in which case it is
returned verbatim.
- a file path, in which case it is opened. Again, like a
file object, if it's uncompressed, a raw file object is
returned, otherwise its read method.
- an object with a :meth:`read` method, in which case that
method is returned.
Returns
-------
fd : context-dependent
See above.
"""
if callable(fd):
yield fd
return
with data.get_readable_fileobj(fd, encoding="binary") as new_fd:
if sys.platform.startswith("win"):
yield new_fd.read
else:
if isinstance(new_fd, io.FileIO):
yield new_fd
else:
yield new_fd.read
def _fast_iterparse(fd, buffersize=2**10):
from xml.parsers import expat
if not callable(fd):
read = fd.read
else:
read = fd
queue = []
text = []
def start(name, attr):
queue.append(
(True, name, attr, (parser.CurrentLineNumber, parser.CurrentColumnNumber))
)
del text[:]
def end(name):
queue.append(
(
False,
name,
"".join(text).strip(),
(parser.CurrentLineNumber, parser.CurrentColumnNumber),
)
)
parser = expat.ParserCreate()
parser.specified_attributes = True
parser.StartElementHandler = start
parser.EndElementHandler = end
parser.CharacterDataHandler = text.append
Parse = parser.Parse
data = read(buffersize)
while data:
Parse(data, False)
yield from queue
del queue[:]
data = read(buffersize)
Parse("", True)
yield from queue
# Try to import the C version of the iterparser, otherwise fall back
# to the Python implementation above.
_slow_iterparse = _fast_iterparse
try:
from . import _iterparser
_fast_iterparse = _iterparser.IterParser
except ImportError:
pass
[docs]
@contextlib.contextmanager
def get_xml_iterator(source, _debug_python_based_parser=False):
"""
Returns an iterator over the elements of an XML file.
The iterator doesn't ever build a tree, so it is much more memory
and time efficient than the alternative in ``cElementTree``.
Parameters
----------
source : path-like, readable file-like, or callable
Handle that contains the data or function that reads it.
If a function or callable object, it must directly read from a stream.
Non-callable objects must define a ``read`` method.
Returns
-------
parts : iterator
The iterator returns 4-tuples (*start*, *tag*, *data*, *pos*):
- *start*: when `True` is a start element event, otherwise
an end element event.
- *tag*: The name of the element
- *data*: Depends on the value of *event*:
- if *start* == `True`, data is a dictionary of
attributes
- if *start* == `False`, data is a string containing
the text content of the element
- *pos*: Tuple (*line*, *col*) indicating the source of the
event.
"""
with _convert_to_fd_or_read_function(source) as fd:
if _debug_python_based_parser:
context = _slow_iterparse(fd)
else:
context = _fast_iterparse(fd)
yield iter(context)
[docs]
def get_xml_encoding(source):
"""
Determine the encoding of an XML file by reading its header.
Parameters
----------
source : path-like, readable file-like, or callable
Handle that contains the data or function that reads it.
If a function or callable object, it must directly read from a stream.
Non-callable objects must define a ``read`` method.
Returns
-------
encoding : str
"""
with get_xml_iterator(source) as iterator:
start, tag, data, pos = next(iterator)
if not start or tag != "xml":
raise OSError("Invalid XML file")
# The XML spec says that no encoding === utf-8
return data.get("encoding") or "utf-8"
[docs]
def xml_readlines(source):
"""
Get the lines from a given XML file. Correctly determines the
encoding and always returns unicode.
Parameters
----------
source : path-like, readable file-like, or callable
Handle that contains the data or function that reads it.
If a function or callable object, it must directly read from a stream.
Non-callable objects must define a ``read`` method.
Returns
-------
lines : list of unicode
"""
encoding = get_xml_encoding(source)
with data.get_readable_fileobj(source, encoding=encoding) as input:
input.seek(0)
xml_lines = input.readlines()
return xml_lines
