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author shellac
date Mon, 01 Jun 2020 08:59:25 -0400
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1 # Human friendly input/output in Python.
2 #
3 # Author: Peter Odding <peter@peterodding.com>
4 # Last Change: June 24, 2017
5 # URL: https://humanfriendly.readthedocs.io
6
7 """
8 Parsing and reformatting of usage messages.
9
10 The :mod:`~humanfriendly.usage` module parses and reformats usage messages:
11
12 - The :func:`format_usage()` function takes a usage message and inserts ANSI
13 escape sequences that highlight items of special significance like command
14 line options, meta variables, etc. The resulting usage message is (intended
15 to be) easier to read on a terminal.
16
17 - The :func:`render_usage()` function takes a usage message and rewrites it to
18 reStructuredText_ suitable for inclusion in the documentation of a Python
19 package. This provides a DRY solution to keeping a single authoritative
20 definition of the usage message while making it easily available in
21 documentation. As a cherry on the cake it's not just a pre-formatted dump of
22 the usage message but a nicely formatted reStructuredText_ fragment.
23
24 - The remaining functions in this module support the two functions above.
25
26 Usage messages in general are free format of course, however the functions in
27 this module assume a certain structure from usage messages in order to
28 successfully parse and reformat them, refer to :func:`parse_usage()` for
29 details.
30
31 .. _DRY: https://en.wikipedia.org/wiki/Don%27t_repeat_yourself
32 .. _reStructuredText: https://en.wikipedia.org/wiki/ReStructuredText
33 """
34
35 # Standard library modules.
36 import csv
37 import functools
38 import logging
39 import re
40
41 # Standard library module or external dependency (see setup.py).
42 from importlib import import_module
43
44 # Modules included in our package.
45 from humanfriendly.compat import StringIO
46 from humanfriendly.text import dedent, split_paragraphs, trim_empty_lines
47
48 # Public identifiers that require documentation.
49 __all__ = (
50 'find_meta_variables',
51 'format_usage',
52 'import_module', # previously exported (backwards compatibility)
53 'inject_usage',
54 'parse_usage',
55 'render_usage',
56 'USAGE_MARKER',
57 )
58
59 USAGE_MARKER = "Usage:"
60 """The string that starts the first line of a usage message."""
61
62 START_OF_OPTIONS_MARKER = "Supported options:"
63 """The string that marks the start of the documented command line options."""
64
65 # Compiled regular expression used to tokenize usage messages.
66 USAGE_PATTERN = re.compile(r'''
67 # Make sure whatever we're matching isn't preceded by a non-whitespace
68 # character.
69 (?<!\S)
70 (
71 # A short command line option or a long command line option
72 # (possibly including a meta variable for a value).
73 (-\w|--\w+(-\w+)*(=\S+)?)
74 # Or ...
75 |
76 # An environment variable.
77 \$[A-Za-z_][A-Za-z0-9_]*
78 # Or ...
79 |
80 # Might be a meta variable (usage() will figure it out).
81 [A-Z][A-Z0-9_]+
82 )
83 ''', re.VERBOSE)
84
85 # Compiled regular expression used to recognize options.
86 OPTION_PATTERN = re.compile(r'^(-\w|--\w+(-\w+)*(=\S+)?)$')
87
88 # Initialize a logger for this module.
89 logger = logging.getLogger(__name__)
90
91
92 def format_usage(usage_text):
93 """
94 Highlight special items in a usage message.
95
96 :param usage_text: The usage message to process (a string).
97 :returns: The usage message with special items highlighted.
98
99 This function highlights the following special items:
100
101 - The initial line of the form "Usage: ..."
102 - Short and long command line options
103 - Environment variables
104 - Meta variables (see :func:`find_meta_variables()`)
105
106 All items are highlighted in the color defined by
107 :data:`.HIGHLIGHT_COLOR`.
108 """
109 # Ugly workaround to avoid circular import errors due to interdependencies
110 # between the humanfriendly.terminal and humanfriendly.usage modules.
111 from humanfriendly.terminal import ansi_wrap, HIGHLIGHT_COLOR
112 formatted_lines = []
113 meta_variables = find_meta_variables(usage_text)
114 for line in usage_text.strip().splitlines(True):
115 if line.startswith(USAGE_MARKER):
116 # Highlight the "Usage: ..." line in bold font and color.
117 formatted_lines.append(ansi_wrap(line, color=HIGHLIGHT_COLOR))
118 else:
119 # Highlight options, meta variables and environment variables.
120 formatted_lines.append(replace_special_tokens(
121 line, meta_variables,
122 lambda token: ansi_wrap(token, color=HIGHLIGHT_COLOR),
123 ))
124 return ''.join(formatted_lines)
125
126
127 def find_meta_variables(usage_text):
128 """
129 Find the meta variables in the given usage message.
130
131 :param usage_text: The usage message to parse (a string).
132 :returns: A list of strings with any meta variables found in the usage
133 message.
134
135 When a command line option requires an argument, the convention is to
136 format such options as ``--option=ARG``. The text ``ARG`` in this example
137 is the meta variable.
138 """
139 meta_variables = set()
140 for match in USAGE_PATTERN.finditer(usage_text):
141 token = match.group(0)
142 if token.startswith('-'):
143 option, _, value = token.partition('=')
144 if value:
145 meta_variables.add(value)
146 return list(meta_variables)
147
148
149 def parse_usage(text):
150 """
151 Parse a usage message by inferring its structure (and making some assumptions :-).
152
153 :param text: The usage message to parse (a string).
154 :returns: A tuple of two lists:
155
156 1. A list of strings with the paragraphs of the usage message's
157 "introduction" (the paragraphs before the documentation of the
158 supported command line options).
159
160 2. A list of strings with pairs of command line options and their
161 descriptions: Item zero is a line listing a supported command
162 line option, item one is the description of that command line
163 option, item two is a line listing another supported command
164 line option, etc.
165
166 Usage messages in general are free format of course, however
167 :func:`parse_usage()` assume a certain structure from usage messages in
168 order to successfully parse them:
169
170 - The usage message starts with a line ``Usage: ...`` that shows a symbolic
171 representation of the way the program is to be invoked.
172
173 - After some free form text a line ``Supported options:`` (surrounded by
174 empty lines) precedes the documentation of the supported command line
175 options.
176
177 - The command line options are documented as follows::
178
179 -v, --verbose
180
181 Make more noise.
182
183 So all of the variants of the command line option are shown together on a
184 separate line, followed by one or more paragraphs describing the option.
185
186 - There are several other minor assumptions, but to be honest I'm not sure if
187 anyone other than me is ever going to use this functionality, so for now I
188 won't list every intricate detail :-).
189
190 If you're curious anyway, refer to the usage message of the `humanfriendly`
191 package (defined in the :mod:`humanfriendly.cli` module) and compare it with
192 the usage message you see when you run ``humanfriendly --help`` and the
193 generated usage message embedded in the readme.
194
195 Feel free to request more detailed documentation if you're interested in
196 using the :mod:`humanfriendly.usage` module outside of the little ecosystem
197 of Python packages that I have been building over the past years.
198 """
199 introduction = []
200 documented_options = []
201 # Split the raw usage message into paragraphs.
202 paragraphs = split_paragraphs(text)
203 # Get the paragraphs that are part of the introduction.
204 while paragraphs:
205 # Check whether we've found the end of the introduction.
206 end_of_intro = (paragraphs[0] == START_OF_OPTIONS_MARKER)
207 # Append the current paragraph to the introduction.
208 introduction.append(paragraphs.pop(0))
209 # Stop after we've processed the complete introduction.
210 if end_of_intro:
211 break
212 logger.debug("Parsed introduction: %s", introduction)
213 # Parse the paragraphs that document command line options.
214 while paragraphs:
215 documented_options.append(dedent(paragraphs.pop(0)))
216 description = []
217 while paragraphs:
218 # Check if the next paragraph starts the documentation of another
219 # command line option. We split on a comma followed by a space so
220 # that our parsing doesn't trip up when the label used for an
221 # option's value contains commas.
222 tokens = [t.strip() for t in re.split(r',\s', paragraphs[0]) if t and not t.isspace()]
223 if all(OPTION_PATTERN.match(t) for t in tokens):
224 break
225 else:
226 description.append(paragraphs.pop(0))
227 # Join the description's paragraphs back together so we can remove
228 # common leading indentation.
229 documented_options.append(dedent('\n\n'.join(description)))
230 logger.debug("Parsed options: %s", documented_options)
231 return introduction, documented_options
232
233
234 def render_usage(text):
235 """
236 Reformat a command line program's usage message to reStructuredText_.
237
238 :param text: The plain text usage message (a string).
239 :returns: The usage message rendered to reStructuredText_ (a string).
240 """
241 meta_variables = find_meta_variables(text)
242 introduction, options = parse_usage(text)
243 output = [render_paragraph(p, meta_variables) for p in introduction]
244 if options:
245 output.append('\n'.join([
246 '.. csv-table::',
247 ' :header: Option, Description',
248 ' :widths: 30, 70',
249 '',
250 ]))
251 csv_buffer = StringIO()
252 csv_writer = csv.writer(csv_buffer)
253 while options:
254 variants = options.pop(0)
255 description = options.pop(0)
256 csv_writer.writerow([
257 render_paragraph(variants, meta_variables),
258 ('\n\n'.join(render_paragraph(p, meta_variables) for p in split_paragraphs(description))).rstrip(),
259 ])
260 csv_lines = csv_buffer.getvalue().splitlines()
261 output.append('\n'.join(' %s' % l for l in csv_lines))
262 logger.debug("Rendered output: %s", output)
263 return '\n\n'.join(trim_empty_lines(o) for o in output)
264
265
266 def inject_usage(module_name):
267 """
268 Use cog_ to inject a usage message into a reStructuredText_ file.
269
270 :param module_name: The name of the module whose ``__doc__`` attribute is
271 the source of the usage message (a string).
272
273 This simple wrapper around :func:`render_usage()` makes it very easy to
274 inject a reformatted usage message into your documentation using cog_. To
275 use it you add a fragment like the following to your ``*.rst`` file::
276
277 .. [[[cog
278 .. from humanfriendly.usage import inject_usage
279 .. inject_usage('humanfriendly.cli')
280 .. ]]]
281 .. [[[end]]]
282
283 The lines in the fragment above are single line reStructuredText_ comments
284 that are not copied to the output. Their purpose is to instruct cog_ where
285 to inject the reformatted usage message. Once you've added these lines to
286 your ``*.rst`` file, updating the rendered usage message becomes really
287 simple thanks to cog_:
288
289 .. code-block:: sh
290
291 $ cog.py -r README.rst
292
293 This will inject or replace the rendered usage message in your
294 ``README.rst`` file with an up to date copy.
295
296 .. _cog: http://nedbatchelder.com/code/cog/
297 """
298 import cog
299 usage_text = import_module(module_name).__doc__
300 cog.out("\n" + render_usage(usage_text) + "\n\n")
301
302
303 def render_paragraph(paragraph, meta_variables):
304 # Reformat the "Usage:" line to highlight "Usage:" in bold and show the
305 # remainder of the line as pre-formatted text.
306 if paragraph.startswith(USAGE_MARKER):
307 tokens = paragraph.split()
308 return "**%s** `%s`" % (tokens[0], ' '.join(tokens[1:]))
309 # Reformat the "Supported options:" line to highlight it in bold.
310 if paragraph == 'Supported options:':
311 return "**%s**" % paragraph
312 # Reformat shell transcripts into code blocks.
313 if re.match(r'^\s*\$\s+\S', paragraph):
314 # Split the paragraph into lines.
315 lines = paragraph.splitlines()
316 # Check if the paragraph is already indented.
317 if not paragraph[0].isspace():
318 # If the paragraph isn't already indented we'll indent it now.
319 lines = [' %s' % line for line in lines]
320 lines.insert(0, '.. code-block:: sh')
321 lines.insert(1, '')
322 return "\n".join(lines)
323 # The following reformatting applies only to paragraphs which are not
324 # indented. Yes this is a hack - for now we assume that indented paragraphs
325 # are code blocks, even though this assumption can be wrong.
326 if not paragraph[0].isspace():
327 # Change UNIX style `quoting' so it doesn't trip up DocUtils.
328 paragraph = re.sub("`(.+?)'", r'"\1"', paragraph)
329 # Escape asterisks.
330 paragraph = paragraph.replace('*', r'\*')
331 # Reformat inline tokens.
332 paragraph = replace_special_tokens(
333 paragraph, meta_variables,
334 lambda token: '``%s``' % token,
335 )
336 return paragraph
337
338
339 def replace_special_tokens(text, meta_variables, replace_fn):
340 return USAGE_PATTERN.sub(functools.partial(
341 replace_tokens_callback,
342 meta_variables=meta_variables,
343 replace_fn=replace_fn
344 ), text)
345
346
347 def replace_tokens_callback(match, meta_variables, replace_fn):
348 token = match.group(0)
349 if not (re.match('^[A-Z][A-Z0-9_]+$', token) and token not in meta_variables):
350 token = replace_fn(token)
351 return token