Sybil parsers are what extracts examples from documentation source files and turns them into parsed examples with evaluators that can check if they are as expected. A number of parsers are included, and it’s simple enough to write your own. The included parsers are as follows:
An additional option flag,
sybil.parsers.doctest.FIX_BYTE_UNICODE_REPR, is provided.
When used, this flag causes byte and unicode literals in doctest expected
output to be rewritten such that they are compatible with the version of
Python with which the tests are executed. If your example output includes either
u'...' and your code is expected to run under both Python 2
and Python 3, then you will likely need this option.
FIX_BYTE_UNICODE_REPR is quite simplistic. It will catch
examples but you may hit problems where, for example,
['b', ''] in expected
output will be rewritten as
['', ''] on Python 2 and
['u', ''] as
on Python 3. To work around this, either only run Sybil on Python 3 and do not
use this option, or pick different example output.
For example, this code block would be evaluated successfully and will define the
prefix_and_print() function in the document’s namespace:
.. code-block:: python import sys def prefix_and_print(message): print('prefix:', message.decode('ascii'))
Including all the boilerplate necessary for an example to successfully evaluate can hinder an example’s usefulness as part of documentation. As a result, this parser also evaluates “invisible” code blocks such as this one:
.. invisible-code-block: python remember_me = b'see how namespaces work?'
These take advantage of Sphinx comment syntax so that the code block will not be rendered in your documentation but can be used to set up the document’s namespace or make assertions about what the evaluation of other examples has put in that namespace.
The parser is used by instantiating
sybil.parsers.codeblock.CodeBlockParser and passing it as an element in
the list passed as the
parsers parameter to
CodeBlockParser takes an optional
future_imports parameter that can be used to prefix all example python
code found by this parser with one or or more
from __future__ import ...
statements. For example, to prefix all code block examples with
from __future__ import print_function, such that they can use Python 3 style
print() calls even when testing the documentation under Python 2, you would
instantiate the parser as follows:
from sybil.parsers.codeblock import CodeBlockParser CodeBlockParser(future_imports=['print_function'])
This parser takes advantage of Sphinx comment syntax to introduce
a special comment that takes the preceding ReST block and inserts its
raw content into the document’s
using the name specified.
A simple example:: root.txt subdir/ subdir/file.txt subdir/logs/ .. -> expected_listing
The above documentation source, when parsed by this parser and then evaluated,
would mean that
expected_listing could be used in other examples in the
>>> expected_listing.split() [u'root.txt', u'subdir/', u'subdir/file.txt', u'subdir/logs/']
This parser takes advantage of Sphinx comment syntax to introduce special comments that allow other examples in the document to be skipped. This can be useful if they include pseudo code or examples that can only be evaluated on a particular version of Python.
.. skip: next This would be wrong: >>> 1 == 2 True
If you need to skip a collection of examples, this can be done as follows:
This is pseudo-code: .. skip: start >>> foo = ... >>> foo(..) .. skip: end
You can also add conditions to either
start as shown below:
.. invisible-code-block: python import sys This will only work on Python 3: .. skip: next if(sys.version_info < (3, 0), reason="python 3 only") >>> repr(b'foo') "b'foo'"
Developing your own parsers¶
Sybil parsers are callables that take a
sybil.document.Document and yield a sequence of
the character position of the start and end of the example in the document’s
text, along with a parsed version of the
example and a callable evaluator. That evaluator will be called with an
Example constructed from the
Document and the
and should either raise an exception or return a textual description in the
event of the example not being as expected. Evaluators may also
modify the document’s
As an example, let’s look at a parser suitable for evaluating bash commands in a subprocess and checking the output is as expected:
.. code-block:: bash $ echo hi there hi there
Writing parsers quite often involves using regular expressions to extract
the text for examples from the document. There’s no hard requirement
for this, but if you find you need to, then
find_region_sources() may be of help.
Parsers are free to access any documented attribute of the
Document although will most likely
only need to work with
namespace attribute should not be
For the above example, the parser could be implemented as follows, with the parsed version consisting of a tuple of the command to run and the expected output:
import re, textwrap from sybil import Region BASHBLOCK_START = re.compile(r'^\.\.\s*code-block::\s*bash') BASHBLOCK_END = re.compile(r'(\n\Z|\n(?=\S))') def parse_bash_blocks(document): for start_match, end_match, source in document.find_region_sources( BASHBLOCK_START, BASHBLOCK_END ): command, output = textwrap.dedent(source).strip().split('\n') assert command.startswith('$ ') parsed = command[2:].split(), output yield Region(start_match.start(), end_match.end(), parsed, evaluate_bash_block)
Evaluators are generally much simpler than parsers and are called with an
Example. Instances of this class are used to wrap up
all the attributes you’re likely to need when writing an evaluator and all
documented attributes are fine to use. In particular,
parsed is the parsed value provided by the parser
when instantiating the
namespace is a reference to the document’s
namespace. Evaluators are free to modify the
namespace if they need to.
For the above example, the evaluator could be implemented as follows:
from subprocess import check_output def evaluate_bash_block(example): command, expected = example.parsed actual = check_output(command).strip().decode('ascii') assert actual == expected, repr(actual) + ' != ' + repr(expected)
The parser can now be used when instantiating a
Sybil, which can
then be used to integrate with your test runner:
from sybil import Sybil sybil = Sybil(parsers=[parse_bash_blocks], pattern='*.rst')