-
-
Notifications
You must be signed in to change notification settings - Fork 564
/
validation.txt
671 lines (490 loc) · 20.2 KB
/
validation.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
====================
Validation with lxml
====================
Apart from the built-in DTD support in parsers, lxml currently supports three
schema languages: DTD_, `Relax NG`_ and `XML Schema`_. All three provide
identical APIs in lxml, represented by validator classes with the obvious
names.
.. _DTD: http://en.wikipedia.org/wiki/Document_Type_Definition
.. _`Relax NG`: http://www.relaxng.org/
.. _`XML Schema`: http://www.w3.org/XML/Schema
lxml also provides support for ISO-`Schematron`_, based on the pure-XSLT
`skeleton implementation`_ of Schematron:
.. _Schematron: http://www.schematron.com
.. _`skeleton implementation`: http://www.schematron.com/implementation.html
There is also basic support for `pre-ISO-Schematron` through the libxml2
Schematron features. However, this does not currently support error reporting
in the validation phase due to insufficiencies in the implementation as of
libxml2 2.6.30.
.. _`pre-ISO-Schematron`: http://www.ascc.net/xml/schematron
.. contents::
..
1 Validation at parse time
2 DTD
3 RelaxNG
4 XMLSchema
5 Schematron
6 (Pre-ISO-Schematron)
The usual setup procedure:
.. sourcecode:: pycon
>>> from lxml import etree
..
>>> try: from StringIO import StringIO
... except ImportError:
... from io import BytesIO
... def StringIO(s):
... if isinstance(s, str): s = s.encode("UTF-8")
... return BytesIO(s)
Validation at parse time
------------------------
The parser in lxml can do on-the-fly validation of a document against
a DTD or an XML schema. The DTD is retrieved automatically based on
the DOCTYPE of the parsed document. All you have to do is use a
parser that has DTD validation enabled:
.. sourcecode:: pycon
>>> parser = etree.XMLParser(dtd_validation=True)
Obviously, a request for validation enables the DTD loading feature.
There are two other options that enable loading the DTD, but that do
not perform any validation. The first is the ``load_dtd`` keyword
option, which simply loads the DTD into the parser and makes it
available to the document as external subset. You can retrieve the
DTD from the parsed document using the ``docinfo`` property of the
result ElementTree object. The internal subset is available as
``internalDTD``, the external subset is provided as ``externalDTD``.
The third way way to activate DTD loading is with the
``attribute_defaults`` option, which loads the DTD and weaves
attribute default values into the document. Again, no validation is
performed unless explicitly requested.
XML schema is supported in a similar way, but requires an explicit
schema to be provided:
.. sourcecode:: pycon
>>> schema_root = etree.XML('''\
... <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
... <xsd:element name="a" type="xsd:integer"/>
... </xsd:schema>
... ''')
>>> schema = etree.XMLSchema(schema_root)
>>> parser = etree.XMLParser(schema = schema)
>>> root = etree.fromstring("<a>5</a>", parser)
If the validation fails (be it for a DTD or an XML schema), the parser
will raise an exception:
.. sourcecode:: pycon
>>> root = etree.fromstring("<a>no int</a>", parser)
Traceback (most recent call last):
lxml.etree.XMLSyntaxError: Element 'a': 'no int' is not a valid value of the atomic type 'xs:integer'.
If you want the parser to succeed regardless of the outcome of the
validation, you should use a non validating parser and run the
validation separately after parsing the document.
DTD
---
As described above, the parser support for DTDs depends on internal or
external subsets of the XML file. This means that the XML file itself
must either contain a DTD or must reference a DTD to make this work.
If you want to validate an XML document against a DTD that is not
referenced by the document itself, you can use the ``DTD`` class.
To use the ``DTD`` class, you must first pass a filename or file-like object
into the constructor to parse a DTD:
.. sourcecode:: pycon
>>> f = StringIO("<!ELEMENT b EMPTY>")
>>> dtd = etree.DTD(f)
Now you can use it to validate documents:
.. sourcecode:: pycon
>>> root = etree.XML("<b/>")
>>> print(dtd.validate(root))
True
>>> root = etree.XML("<b><a/></b>")
>>> print(dtd.validate(root))
False
The reason for the validation failure can be found in the error log:
.. sourcecode:: pycon
>>> print(dtd.error_log.filter_from_errors()[0])
<string>:1:0:ERROR:VALID:DTD_NOT_EMPTY: Element b was declared EMPTY this one has content
As an alternative to parsing from a file, you can use the
``external_id`` keyword argument to parse from a catalog. The
following example reads the DocBook DTD in version 4.2, if available
in the system catalog:
.. sourcecode:: python
dtd = etree.DTD(external_id = "-//OASIS//DTD DocBook XML V4.2//EN")
The DTD information is available as attributes on the DTD object. The method
``iterelements`` provides an iterator over the element declarations:
.. sourcecode:: pycon
>>> dtd = etree.DTD(StringIO('<!ELEMENT a EMPTY><!ELEMENT b EMPTY>'))
>>> for el in dtd.iterelements():
... print(el.name)
a
b
The method ``elements`` returns the element declarations as a list:
.. sourcecode:: pycon
>>> dtd = etree.DTD(StringIO('<!ELEMENT a EMPTY><!ELEMENT b EMPTY>'))
>>> len(dtd.elements())
2
An element declaration object provides the following attributes/methods:
- ``name``: The name of the element;
- ``type``: The element type, one of "undefined", "empty", "any", "mixed" or "element";
- ``content``: Element content declaration (see below);
- ``iterattributes()``: Return an iterator over attribute declarations (see below);
- ``attributes()``: Return a list of attribute declarations.
The ``content`` attribute contains information about the content model of the element.
These element content declaration objects form a binary tree (via the ``left`` and ``right``
attributes), that makes it possible to reconstruct the content model expression. Here's a
list of all attributes:
- ``name``: If this object represents an element in the content model expression,
``name`` is the name of the element, otherwise it is ``None``;
- ``type``: The type of the node: one of "pcdata", "element", "seq" or "or";
- ``occur``: How often this element (or this combination of elements) may occur:
one of "once", "opt", "mult" or "plus"
- ``left``: The left hand subexpression
- ``right``: The right hand subexpression
For example, the element declaration ``<!ELEMENT a (a|b)+>`` results
in the following element content declaration objects:
.. sourcecode:: pycon
>>> dtd = etree.DTD(StringIO('<!ELEMENT a (a|b)+>'))
>>> content = dtd.elements()[0].content
>>> content.type, content.occur, content.name
('or', 'plus', None)
>>> left, right = content.left, content.right
>>> left.type, left.occur, left.name
('element', 'once', 'a')
>>> right.type, right.occur, right.name
('element', 'once', 'b')
Attributes declarations have the following attributes/methods:
- ``name``: The name of the attribute;
- ``elemname``: The name of the element the attribute belongs to;
- ``type``: The attribute type, one of "cdata", "id", "idref", "idrefs", "entity",
"entities", "nmtoken", "nmtokens", "enumeration" or "notation";
- ``default``: The type of the default value, one of "none", "required", "implied"
or "fixed";
- ``defaultValue``: The default value;
- ``itervalues()``: Return an iterator over the allowed attribute values (if the attribute
if of type "enumeration");
- ``values()``: Return a list of allowed attribute values.
Entity declarations are available via the ``iterentities`` and ``entities`` methods:
>>> dtd = etree.DTD(StringIO('<!ENTITY hurz "@">'))
>>> entity = dtd.entities()[0]
>>> entity.name, entity.orig, entity.content
('hurz', '@', '@')
RelaxNG
-------
The ``RelaxNG`` class takes an ElementTree object to construct a Relax NG
validator:
.. sourcecode:: pycon
>>> f = StringIO('''\
... <element name="a" xmlns="http://relaxng.org/ns/structure/1.0">
... <zeroOrMore>
... <element name="b">
... <text />
... </element>
... </zeroOrMore>
... </element>
... ''')
>>> relaxng_doc = etree.parse(f)
>>> relaxng = etree.RelaxNG(relaxng_doc)
Alternatively, pass a filename to the ``file`` keyword argument to parse from
a file. This also enables correct handling of include files from within the
RelaxNG parser.
You can then validate some ElementTree document against the schema. You'll get
back True if the document is valid against the Relax NG schema, and False if
not:
.. sourcecode:: pycon
>>> valid = StringIO('<a><b></b></a>')
>>> doc = etree.parse(valid)
>>> relaxng.validate(doc)
True
>>> invalid = StringIO('<a><c></c></a>')
>>> doc2 = etree.parse(invalid)
>>> relaxng.validate(doc2)
False
Calling the schema object has the same effect as calling its validate
method. This is sometimes used in conditional statements:
.. sourcecode:: pycon
>>> invalid = StringIO('<a><c></c></a>')
>>> doc2 = etree.parse(invalid)
>>> if not relaxng(doc2):
... print("invalid!")
invalid!
If you prefer getting an exception when validating, you can use the
``assert_`` or ``assertValid`` methods:
.. sourcecode:: pycon
>>> relaxng.assertValid(doc2)
Traceback (most recent call last):
...
lxml.etree.DocumentInvalid: Did not expect element c there, line 1
>>> relaxng.assert_(doc2)
Traceback (most recent call last):
...
AssertionError: Did not expect element c there, line 1
If you want to find out why the validation failed in the second case, you can
look up the error log of the validation process and check it for relevant
messages:
.. sourcecode:: pycon
>>> log = relaxng.error_log
>>> print(log.last_error)
<string>:1:0:ERROR:RELAXNGV:RELAXNG_ERR_ELEMWRONG: Did not expect element c there
You can see that the error (ERROR) happened during RelaxNG validation
(RELAXNGV). The message then tells you what went wrong. You can also
look at the error domain and its type directly:
.. sourcecode:: pycon
>>> error = log.last_error
>>> print(error.domain_name)
RELAXNGV
>>> print(error.type_name)
RELAXNG_ERR_ELEMWRONG
Note that this error log is local to the RelaxNG object. It will only
contain log entries that appeared during the validation.
Similar to XSLT, there's also a less efficient but easier shortcut method to
do one-shot RelaxNG validation:
.. sourcecode:: pycon
>>> doc.relaxng(relaxng_doc)
True
>>> doc2.relaxng(relaxng_doc)
False
libxml2 does not currently support the `RelaxNG Compact Syntax`_.
However, the trang_ translator can convert the compact syntax to the
XML syntax, which can then be used with lxml.
.. _`RelaxNG Compact Syntax`:
.. _trang: http://www.thaiopensource.com/relaxng/trang.html
XMLSchema
---------
lxml.etree also has XML Schema (XSD) support, using the class
lxml.etree.XMLSchema. The API is very similar to the Relax NG and DTD
classes. Pass an ElementTree object to construct a XMLSchema validator:
.. sourcecode:: pycon
>>> f = StringIO('''\
... <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
... <xsd:element name="a" type="AType"/>
... <xsd:complexType name="AType">
... <xsd:sequence>
... <xsd:element name="b" type="xsd:string" />
... </xsd:sequence>
... </xsd:complexType>
... </xsd:schema>
... ''')
>>> xmlschema_doc = etree.parse(f)
>>> xmlschema = etree.XMLSchema(xmlschema_doc)
You can then validate some ElementTree document with this. Like with RelaxNG,
you'll get back true if the document is valid against the XML schema, and
false if not:
.. sourcecode:: pycon
>>> valid = StringIO('<a><b></b></a>')
>>> doc = etree.parse(valid)
>>> xmlschema.validate(doc)
True
>>> invalid = StringIO('<a><c></c></a>')
>>> doc2 = etree.parse(invalid)
>>> xmlschema.validate(doc2)
False
Calling the schema object has the same effect as calling its validate method.
This is sometimes used in conditional statements:
.. sourcecode:: pycon
>>> invalid = StringIO('<a><c></c></a>')
>>> doc2 = etree.parse(invalid)
>>> if not xmlschema(doc2):
... print("invalid!")
invalid!
If you prefer getting an exception when validating, you can use the
``assert_`` or ``assertValid`` methods:
.. sourcecode:: pycon
>>> xmlschema.assertValid(doc2)
Traceback (most recent call last):
...
lxml.etree.DocumentInvalid: Element 'c': This element is not expected. Expected is ( b )., line 1
>>> xmlschema.assert_(doc2)
Traceback (most recent call last):
...
AssertionError: Element 'c': This element is not expected. Expected is ( b )., line 1
Error reporting works as for the RelaxNG class:
.. sourcecode:: pycon
>>> log = xmlschema.error_log
>>> error = log.last_error
>>> print(error.domain_name)
SCHEMASV
>>> print(error.type_name)
SCHEMAV_ELEMENT_CONTENT
If you were to print this log entry, you would get something like the
following. Note that the error message depends on the libxml2 version in
use::
<string>:1:ERROR::SCHEMAV_ELEMENT_CONTENT: Element 'c': This element is not expected. Expected is ( b ).
Similar to XSLT and RelaxNG, there's also a less efficient but easier shortcut
method to do XML Schema validation:
.. sourcecode:: pycon
>>> doc.xmlschema(xmlschema_doc)
True
>>> doc2.xmlschema(xmlschema_doc)
False
Schematron
----------
From version 2.3 on lxml features ISO-`Schematron`_ support built on the
de-facto reference implementation of Schematron, the pure-XSLT-1.0
`skeleton implementation`_. This is provided by the lxml.isoschematron package
that implements the Schematron class, with an API compatible to the other
validators'. Pass an Element or ElementTree object to construct a Schematron
validator:
.. sourcecode:: pycon
>>> from lxml import isoschematron
>>> f = StringIO('''\
... <schema xmlns="http://purl.oclc.org/dsdl/schematron" >
... <pattern id="sum_equals_100_percent">
... <title>Sum equals 100%.</title>
... <rule context="Total">
... <assert test="sum(//Percent)=100">Sum is not 100%.</assert>
... </rule>
... </pattern>
... </schema>
... ''')
>>> sct_doc = etree.parse(f)
>>> schematron = isoschematron.Schematron(sct_doc)
You can then validate some ElementTree document with this. Just like with
XMLSchema or RelaxNG, you'll get back true if the document is valid against the
schema, and false if not:
.. sourcecode:: pycon
>>> valid = StringIO('''\
... <Total>
... <Percent>20</Percent>
... <Percent>30</Percent>
... <Percent>50</Percent>
... </Total>
... ''')
>>> doc = etree.parse(valid)
>>> schematron.validate(doc)
True
>>> etree.SubElement(doc.getroot(), "Percent").text = "10"
>>> schematron.validate(doc)
False
Calling the schema object has the same effect as calling its validate method.
This can be useful for conditional statements:
.. sourcecode:: pycon
>>> is_valid = isoschematron.Schematron(sct_doc)
>>> if not is_valid(doc):
... print("invalid!")
invalid!
Built on a pure-xslt implementation, the actual validator is created as an
XSLT 1.0 stylesheet using these steps:
0. (Extract embedded Schematron from XML Schema or RelaxNG schema)
1. Process inclusions
2. Process abstract patterns
3. Compile the schematron schema to XSLT
To allow more control over the individual steps, isoschematron.Schematron
supports an extended API:
The ``include`` and ``expand`` keyword arguments can be used to switch off
steps 1) and 2).
To set parameters for steps 1), 2) and 3) dictionaries containing parameters
for XSLT can be provided using the keyword arguments ``include_params``,
``expand_params`` or ``compile_params``. Schematron automatically converts these
parameters to stylesheet parameters so you need not worry to set string
parameters using quotes or to use XSLT.strparam(). If you ever need to pass an
XPath as argument to the XSLT stylesheet you can pass in an etree.XPath object
(see XPath and XSLT with lxml: Stylesheet-parameters_ for background on this).
The ``phase`` parameter of the compile step is additionally exposed as a keyword
argument. If set, it overrides occurrence in ``compile_params``. Note that
isoschematron.Schematron might expose more common parameters as additional keyword
args in the future.
By setting ``store_schematron`` to True, the (included-and-expanded) schematron
document tree is stored and made available through the ``schematron`` property.
Similarly, setting ``store_xslt`` to True will result in the validation XSLT
document tree being kept; it can be retrieved through the ``validator_xslt``
property.
Finally, with ``store_report`` set to True (default: False), the resulting
validation report document gets stored and can be accessed as the
``validation_report`` property.
.. _Stylesheet-parameters: xpathxslt.html#stylesheet-parameters
Using the ``phase`` parameter of isoschematron.Schematron allows for selective
validation of predefined pattern groups:
.. sourcecode:: pycon
>>> f = StringIO('''\
... <schema xmlns="http://purl.oclc.org/dsdl/schematron" >
... <phase id="phase.sum_check">
... <active pattern="sum_equals_100_percent"/>
... </phase>
... <phase id="phase.entries_check">
... <active pattern="all_positive"/>
... </phase>
... <pattern id="sum_equals_100_percent">
... <title>Sum equals 100%.</title>
... <rule context="Total">
... <assert test="sum(//Percent)=100">Sum is not 100%.</assert>
... </rule>
... </pattern>
... <pattern id="all_positive">
... <title>All entries must be positive.</title>
... <rule context="Percent">
... <assert test="number(.)>0">Number (<value-of select="."/>) not positive</assert>
... </rule>
... </pattern>
... </schema>
... ''')
>>> sct_doc = etree.parse(f)
>>> schematron = isoschematron.Schematron(sct_doc)
>>> valid = StringIO('''\
... <Total>
... <Percent>20</Percent>
... <Percent>30</Percent>
... <Percent>50</Percent>
... </Total>
... ''')
>>> doc = etree.parse(valid)
>>> schematron.validate(doc)
True
>>> invalid_positive = StringIO('''\
... <Total>
... <Percent>0</Percent>
... <Percent>50</Percent>
... <Percent>50</Percent>
... </Total>
... ''')
>>> doc = etree.parse(invalid_positive)
>>> schematron.validate(doc)
False
If the constraint of Percent entries being positive is not of interest in a
certain validation scenario, it can now be disabled:
.. sourcecode:: pycon
>>> selective = isoschematron.Schematron(sct_doc, phase="phase.sum_check")
>>> selective.validate(doc)
True
The usage of validation phases is a unique feature of ISO-Schematron and can be
a very powerful tool e.g. for establishing validation stages or to provide
different validators for different "validation audiences".
(Pre-ISO-Schematron)
--------------------
Since version 2.0, lxml.etree features `pre-ISO-Schematron`_ support, using the
class lxml.etree.Schematron. It requires at least libxml2 2.6.21 to
work. The API is the same as for the other validators. Pass an
ElementTree object to construct a Schematron validator:
.. sourcecode:: pycon
>>> f = StringIO('''\
... <schema xmlns="http://www.ascc.net/xml/schematron" >
... <pattern name="Sum equals 100%.">
... <rule context="Total">
... <assert test="sum(//Percent)=100">Sum is not 100%.</assert>
... </rule>
... </pattern>
... </schema>
... ''')
>>> sct_doc = etree.parse(f)
>>> schematron = etree.Schematron(sct_doc)
You can then validate some ElementTree document with this. Like with RelaxNG,
you'll get back true if the document is valid against the schema, and false if
not:
.. sourcecode:: pycon
>>> valid = StringIO('''\
... <Total>
... <Percent>20</Percent>
... <Percent>30</Percent>
... <Percent>50</Percent>
... </Total>
... ''')
>>> doc = etree.parse(valid)
>>> schematron.validate(doc)
True
>>> etree.SubElement(doc.getroot(), "Percent").text = "10"
>>> schematron.validate(doc)
False
Calling the schema object has the same effect as calling its validate method.
This is sometimes used in conditional statements:
.. sourcecode:: pycon
>>> is_valid = etree.Schematron(sct_doc)
>>> if not is_valid(doc):
... print("invalid!")
invalid!
Note that libxml2 restricts error reporting to the parsing step (when creating
the Schematron instance). There is not currently any support for error
reporting during validation.