]> jfr.im git - yt-dlp.git/blob - CONTRIBUTING.md
[extractor] Allow non-fatal `title` extraction
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1 # CONTRIBUTING TO YT-DLP
2
3 - [OPENING AN ISSUE](#opening-an-issue)
4 - [Is the description of the issue itself sufficient?](#is-the-description-of-the-issue-itself-sufficient)
5 - [Are you using the latest version?](#are-you-using-the-latest-version)
6 - [Is the issue already documented?](#is-the-issue-already-documented)
7 - [Why are existing options not enough?](#why-are-existing-options-not-enough)
8 - [Have you read and understood the changes, between youtube-dl and yt-dlp](#have-you-read-and-understood-the-changes-between-youtube-dl-and-yt-dlp)
9 - [Is there enough context in your bug report?](#is-there-enough-context-in-your-bug-report)
10 - [Does the issue involve one problem, and one problem only?](#does-the-issue-involve-one-problem-and-one-problem-only)
11 - [Is anyone going to need the feature?](#is-anyone-going-to-need-the-feature)
12 - [Is your question about yt-dlp?](#is-your-question-about-yt-dlp)
13 - [Are you willing to share account details if needed?](#are-you-willing-to-share-account-details-if-needed)
14 - [DEVELOPER INSTRUCTIONS](#developer-instructions)
15 - [Adding new feature or making overarching changes](#adding-new-feature-or-making-overarching-changes)
16 - [Adding support for a new site](#adding-support-for-a-new-site)
17 - [yt-dlp coding conventions](#yt-dlp-coding-conventions)
18 - [Mandatory and optional metafields](#mandatory-and-optional-metafields)
19 - [Provide fallbacks](#provide-fallbacks)
20 - [Regular expressions](#regular-expressions)
21 - [Long lines policy](#long-lines-policy)
22 - [Quotes](#quotes)
23 - [Inline values](#inline-values)
24 - [Collapse fallbacks](#collapse-fallbacks)
25 - [Trailing parentheses](#trailing-parentheses)
26 - [Use convenience conversion and parsing functions](#use-convenience-conversion-and-parsing-functions)
27 - [EMBEDDING YT-DLP](README.md#embedding-yt-dlp)
28
29
30
31 # OPENING AN ISSUE
32
33 Bugs and suggestions should be reported at: [yt-dlp/yt-dlp/issues](https://github.com/yt-dlp/yt-dlp/issues). Unless you were prompted to or there is another pertinent reason (e.g. GitHub fails to accept the bug report), please do not send bug reports via personal email. For discussions, join us in our [discord server](https://discord.gg/H5MNcFW63r).
34
35 **Please include the full output of yt-dlp when run with `-vU`**, i.e. **add** `-vU` flag to **your command line**, copy the **whole** output and post it in the issue body wrapped in \`\`\` for better formatting. It should look similar to this:
36 ```
37 $ yt-dlp -vU <your command line>
38 [debug] Command-line config: ['-v', 'demo.com']
39 [debug] Encodings: locale UTF-8, fs utf-8, out utf-8, pref UTF-8
40 [debug] yt-dlp version 2021.09.25 (zip)
41 [debug] Python version 3.8.10 (CPython 64bit) - Linux-5.4.0-74-generic-x86_64-with-glibc2.29
42 [debug] exe versions: ffmpeg 4.2.4, ffprobe 4.2.4
43 [debug] Proxy map: {}
44 Current Build Hash 25cc412d1d3c0725a1f2f5b7e4682f6fb40e6d15f7024e96f7afd572e9919535
45 yt-dlp is up to date (2021.09.25)
46 ...
47 ```
48 **Do not post screenshots of verbose logs; only plain text is acceptable.**
49
50 The output (including the first lines) contains important debugging information. Issues without the full output are often not reproducible and therefore will be closed as `incomplete`.
51
52 The templates provided for the Issues, should be completed and **not removed**, this helps aide the resolution of the issue.
53
54 Please re-read your issue once again to avoid a couple of common mistakes (you can and should use this as a checklist):
55
56 ### Is the description of the issue itself sufficient?
57
58 We often get issue reports that we cannot really decipher. While in most cases we eventually get the required information after asking back multiple times, this poses an unnecessary drain on our resources.
59
60 So please elaborate on what feature you are requesting, or what bug you want to be fixed. Make sure that it's obvious
61
62 - What the problem is
63 - How it could be fixed
64 - How your proposed solution would look like
65
66 If your report is shorter than two lines, it is almost certainly missing some of these, which makes it hard for us to respond to it. We're often too polite to close the issue outright, but the missing info makes misinterpretation likely. We often get frustrated by these issues, since the only possible way for us to move forward on them is to ask for clarification over and over.
67
68 For bug reports, this means that your report should contain the **complete** output of yt-dlp when called with the `-vU` flag. The error message you get for (most) bugs even says so, but you would not believe how many of our bug reports do not contain this information.
69
70 If the error is `ERROR: Unable to extract ...` and you cannot reproduce it from multiple countries, add `--write-pages` and upload the `.dump` files you get [somewhere](https://gist.github.com).
71
72 **Site support requests must contain an example URL**. An example URL is a URL you might want to download, like `https://www.youtube.com/watch?v=BaW_jenozKc`. There should be an obvious video present. Except under very special circumstances, the main page of a video service (e.g. `https://www.youtube.com/`) is *not* an example URL.
73
74 ### Are you using the latest version?
75
76 Before reporting any issue, type `yt-dlp -U`. This should report that you're up-to-date. This goes for feature requests as well.
77
78 ### Is the issue already documented?
79
80 Make sure that someone has not already opened the issue you're trying to open. Search at the top of the window or browse the [GitHub Issues](https://github.com/yt-dlp/yt-dlp/search?type=Issues) of this repository. If there is an issue, feel free to write something along the lines of "This affects me as well, with version 2021.01.01. Here is some more information on the issue: ...". While some issues may be old, a new post into them often spurs rapid activity.
81
82 Additionally, it is also helpful to see if the issue has already been documented in the [youtube-dl issue tracker](https://github.com/ytdl-org/youtube-dl/issues). If similar issues have already been reported in youtube-dl (but not in our issue tracker), links to them can be included in your issue report here.
83
84 ### Why are existing options not enough?
85
86 Before requesting a new feature, please have a quick peek at [the list of supported options](README.md#usage-and-options). Many feature requests are for features that actually exist already! Please, absolutely do show off your work in the issue report and detail how the existing similar options do *not* solve your problem.
87
88 ### Have you read and understood the changes, between youtube-dl and yt-dlp
89
90 There are many changes between youtube-dl and yt-dlp [(changes to default behavior)](README.md#differences-in-default-behavior), and some of the options available have a different behaviour in yt-dlp, or have been removed all together [(list of changes to options)](README.md#deprecated-options). Make sure you have read and understand the differences in the options and how this may impact your downloads before opening an issue.
91
92 ### Is there enough context in your bug report?
93
94 People want to solve problems, and often think they do us a favor by breaking down their larger problems (e.g. wanting to skip already downloaded files) to a specific request (e.g. requesting us to look whether the file exists before downloading the info page). However, what often happens is that they break down the problem into two steps: One simple, and one impossible (or extremely complicated one).
95
96 We are then presented with a very complicated request when the original problem could be solved far easier, e.g. by recording the downloaded video IDs in a separate file. To avoid this, you must include the greater context where it is non-obvious. In particular, every feature request that does not consist of adding support for a new site should contain a use case scenario that explains in what situation the missing feature would be useful.
97
98 ### Does the issue involve one problem, and one problem only?
99
100 Some of our users seem to think there is a limit of issues they can or should open. There is no limit of issues they can or should open. While it may seem appealing to be able to dump all your issues into one ticket, that means that someone who solves one of your issues cannot mark the issue as closed. Typically, reporting a bunch of issues leads to the ticket lingering since nobody wants to attack that behemoth, until someone mercifully splits the issue into multiple ones.
101
102 In particular, every site support request issue should only pertain to services at one site (generally under a common domain, but always using the same backend technology). Do not request support for vimeo user videos, White house podcasts, and Google Plus pages in the same issue. Also, make sure that you don't post bug reports alongside feature requests. As a rule of thumb, a feature request does not include outputs of yt-dlp that are not immediately related to the feature at hand. Do not post reports of a network error alongside the request for a new video service.
103
104 ### Is anyone going to need the feature?
105
106 Only post features that you (or an incapacitated friend you can personally talk to) require. Do not post features because they seem like a good idea. If they are really useful, they will be requested by someone who requires them.
107
108 ### Is your question about yt-dlp?
109
110 Some bug reports are completely unrelated to yt-dlp and relate to a different, or even the reporter's own, application. Please make sure that you are actually using yt-dlp. If you are using a UI for yt-dlp, report the bug to the maintainer of the actual application providing the UI. In general, if you are unable to provide the verbose log, you should not be opening the issue here.
111
112 If the issue is with `youtube-dl` (the upstream fork of yt-dlp) and not with yt-dlp, the issue should be raised in the youtube-dl project.
113
114 ### Are you willing to share account details if needed?
115
116 The maintainers and potential contributors of the project often do not have an account for the website you are asking support for. So any developer interested in solving your issue may ask you for account details. It is your personal discression whether you are willing to share the account in order for the developer to try and solve your issue. However, if you are unwilling or unable to provide details, they obviously cannot work on the issue and it cannot be solved unless some developer who both has an account and is willing/able to contribute decides to solve it.
117
118 By sharing an account with anyone, you agree to bear all risks associated with it. The maintainers and yt-dlp can't be held responsible for any misuse of the credentials.
119
120 While these steps won't necessarily ensure that no misuse of the account takes place, these are still some good practices to follow.
121
122 - Look for people with `Member` (maintainers of the project) or `Contributor` (people who have previously contributed code) tag on their messages.
123 - Change the password before sharing the account to something random (use [this](https://passwordsgenerator.net/) if you don't have a random password generator).
124 - Change the password after receiving the account back.
125
126
127
128
129 # DEVELOPER INSTRUCTIONS
130
131 Most users do not need to build yt-dlp and can [download the builds](https://github.com/yt-dlp/yt-dlp/releases) or get them via [the other installation methods](README.md#installation).
132
133 To run yt-dlp as a developer, you don't need to build anything either. Simply execute
134
135 python -m yt_dlp
136
137 To run the test, simply invoke your favorite test runner, or execute a test file directly; any of the following work:
138
139 python -m unittest discover
140 python test/test_download.py
141 nosetests
142 pytest
143
144 See item 6 of [new extractor tutorial](#adding-support-for-a-new-site) for how to run extractor specific test cases.
145
146 If you want to create a build of yt-dlp yourself, you can follow the instructions [here](README.md#compile).
147
148
149 ## Adding new feature or making overarching changes
150
151 Before you start writing code for implementing a new feature, open an issue explaining your feature request and atleast one use case. This allows the maintainers to decide whether such a feature is desired for the project in the first place, and will provide an avenue to discuss some implementation details. If you open a pull request for a new feature without discussing with us first, do not be surprised when we ask for large changes to the code, or even reject it outright.
152
153 The same applies for changes to the documentation, code style, or overarching changes to the architecture
154
155
156 ## Adding support for a new site
157
158 If you want to add support for a new site, first of all **make sure** this site is **not dedicated to [copyright infringement](https://www.github.com/ytdl-org/youtube-dl#can-you-add-support-for-this-anime-video-site-or-site-which-shows-current-movies-for-free)**. yt-dlp does **not support** such sites thus pull requests adding support for them **will be rejected**.
159
160 After you have ensured this site is distributing its content legally, you can follow this quick list (assuming your service is called `yourextractor`):
161
162 1. [Fork this repository](https://github.com/yt-dlp/yt-dlp/fork)
163 1. Check out the source code with:
164
165 git clone git@github.com:YOUR_GITHUB_USERNAME/yt-dlp.git
166
167 1. Start a new git branch with
168
169 cd yt-dlp
170 git checkout -b yourextractor
171
172 1. Start with this simple template and save it to `yt_dlp/extractor/yourextractor.py`:
173
174 ```python
175 # coding: utf-8
176 from .common import InfoExtractor
177
178
179 class YourExtractorIE(InfoExtractor):
180 _VALID_URL = r'https?://(?:www\.)?yourextractor\.com/watch/(?P<id>[0-9]+)'
181 _TESTS = [{
182 'url': 'https://yourextractor.com/watch/42',
183 'md5': 'TODO: md5 sum of the first 10241 bytes of the video file (use --test)',
184 'info_dict': {
185 'id': '42',
186 'ext': 'mp4',
187 'title': 'Video title goes here',
188 'thumbnail': r're:^https?://.*\.jpg$',
189 # TODO more properties, either as:
190 # * A value
191 # * MD5 checksum; start the string with md5:
192 # * A regular expression; start the string with re:
193 # * Any Python type (for example int or float)
194 }
195 }]
196
197 def _real_extract(self, url):
198 video_id = self._match_id(url)
199 webpage = self._download_webpage(url, video_id)
200
201 # TODO more code goes here, for example ...
202 title = self._html_search_regex(r'<h1>(.+?)</h1>', webpage, 'title')
203
204 return {
205 'id': video_id,
206 'title': title,
207 'description': self._og_search_description(webpage),
208 'uploader': self._search_regex(r'<div[^>]+id="uploader"[^>]*>([^<]+)<', webpage, 'uploader', fatal=False),
209 # TODO more properties (see yt_dlp/extractor/common.py)
210 }
211 ```
212 1. Add an import in [`yt_dlp/extractor/extractors.py`](yt_dlp/extractor/extractors.py).
213 1. Run `python test/test_download.py TestDownload.test_YourExtractor`. This *should fail* at first, but you can continually re-run it until you're done. If you decide to add more than one test, the tests will then be named `TestDownload.test_YourExtractor`, `TestDownload.test_YourExtractor_1`, `TestDownload.test_YourExtractor_2`, etc. Note that tests with `only_matching` key in test's dict are not counted in. You can also run all the tests in one go with `TestDownload.test_YourExtractor_all`
214 1. Make sure you have atleast one test for your extractor. Even if all videos covered by the extractor are expected to be inaccessible for automated testing, tests should still be added with a `skip` parameter indicating why the particular test is disabled from running.
215 1. Have a look at [`yt_dlp/extractor/common.py`](yt_dlp/extractor/common.py) for possible helper methods and a [detailed description of what your extractor should and may return](yt_dlp/extractor/common.py#L91-L426). Add tests and code for as many as you want.
216 1. Make sure your code follows [yt-dlp coding conventions](#yt-dlp-coding-conventions) and check the code with [flake8](https://flake8.pycqa.org/en/latest/index.html#quickstart):
217
218 $ flake8 yt_dlp/extractor/yourextractor.py
219
220 1. Make sure your code works under all [Python](https://www.python.org/) versions supported by yt-dlp, namely CPython and PyPy for Python 3.6 and above. Backward compatibility is not required for even older versions of Python.
221 1. When the tests pass, [add](https://git-scm.com/docs/git-add) the new files, [commit](https://git-scm.com/docs/git-commit) them and [push](https://git-scm.com/docs/git-push) the result, like this:
222
223 $ git add yt_dlp/extractor/extractors.py
224 $ git add yt_dlp/extractor/yourextractor.py
225 $ git commit -m '[yourextractor] Add extractor'
226 $ git push origin yourextractor
227
228 1. Finally, [create a pull request](https://help.github.com/articles/creating-a-pull-request). We'll then review and merge it.
229
230 In any case, thank you very much for your contributions!
231
232 **Tip:** To test extractors that require login information, create a file `test/local_parameters.json` and add `"usenetrc": true` or your username and password in it:
233 ```json
234 {
235 "username": "your user name",
236 "password": "your password"
237 }
238 ```
239
240 ## yt-dlp coding conventions
241
242 This section introduces a guide lines for writing idiomatic, robust and future-proof extractor code.
243
244 Extractors are very fragile by nature since they depend on the layout of the source data provided by 3rd party media hosters out of your control and this layout tends to change. As an extractor implementer your task is not only to write code that will extract media links and metadata correctly but also to minimize dependency on the source's layout and even to make the code foresee potential future changes and be ready for that. This is important because it will allow the extractor not to break on minor layout changes thus keeping old yt-dlp versions working. Even though this breakage issue may be easily fixed by a new version of yt-dlp, this could take some time, during which the the extractor will remain broken.
245
246
247 ### Mandatory and optional metafields
248
249 For extraction to work yt-dlp relies on metadata your extractor extracts and provides to yt-dlp expressed by an [information dictionary](yt_dlp/extractor/common.py#L91-L426) or simply *info dict*. Only the following meta fields in the *info dict* are considered mandatory for a successful extraction process by yt-dlp:
250
251 - `id` (media identifier)
252 - `title` (media title)
253 - `url` (media download URL) or `formats`
254
255 The aforementioned metafields are the critical data that the extraction does not make any sense without and if any of them fail to be extracted then the extractor is considered completely broken. While all extractors must return a `title`, they must also allow it's extraction to be non-fatal.
256
257 The extractor is allowed to return the info dict without url or formats in some special cases if it allows the user to extract usefull information with `--ignore-no-formats-error` - Eg: when the video is a live stream that has not started yet.
258
259 [Any field](yt_dlp/extractor/common.py#219-L426) apart from the aforementioned ones are considered **optional**. That means that extraction should be **tolerant** to situations when sources for these fields can potentially be unavailable (even if they are always available at the moment) and **future-proof** in order not to break the extraction of general purpose mandatory fields.
260
261 #### Example
262
263 Say you have some source dictionary `meta` that you've fetched as JSON with HTTP request and it has a key `summary`:
264
265 ```python
266 meta = self._download_json(url, video_id)
267 ```
268
269 Assume at this point `meta`'s layout is:
270
271 ```python
272 {
273 "summary": "some fancy summary text",
274 "user": {
275 "name": "uploader name"
276 },
277 ...
278 }
279 ```
280
281 Assume you want to extract `summary` and put it into the resulting info dict as `description`. Since `description` is an optional meta field you should be ready that this key may be missing from the `meta` dict, so that you should extract it like:
282
283 ```python
284 description = meta.get('summary') # correct
285 ```
286
287 and not like:
288
289 ```python
290 description = meta['summary'] # incorrect
291 ```
292
293 The latter will break extraction process with `KeyError` if `summary` disappears from `meta` at some later time but with the former approach extraction will just go ahead with `description` set to `None` which is perfectly fine (remember `None` is equivalent to the absence of data).
294
295
296 If the data is nested, do not use `.get` chains, but instead make use of the utility functions `try_get` or `traverse_obj`
297
298 Considering the above `meta` again, assume you want to extract `["user"]["name"]` and put it in the resulting info dict as `uploader`
299
300 ```python
301 uploader = try_get(meta, lambda x: x['user']['name']) # correct
302 ```
303 or
304 ```python
305 uploader = traverse_obj(meta, ('user', 'name')) # correct
306 ```
307
308 and not like:
309
310 ```python
311 uploader = meta['user']['name'] # incorrect
312 ```
313 or
314 ```python
315 uploader = meta.get('user', {}).get('name') # incorrect
316 ```
317
318
319 Similarly, you should pass `fatal=False` when extracting optional data from a webpage with `_search_regex`, `_html_search_regex` or similar methods, for instance:
320
321 ```python
322 description = self._search_regex(
323 r'<span[^>]+id="title"[^>]*>([^<]+)<',
324 webpage, 'description', fatal=False)
325 ```
326
327 With `fatal` set to `False` if `_search_regex` fails to extract `description` it will emit a warning and continue extraction.
328
329 You can also pass `default=<some fallback value>`, for example:
330
331 ```python
332 description = self._search_regex(
333 r'<span[^>]+id="title"[^>]*>([^<]+)<',
334 webpage, 'description', default=None)
335 ```
336
337 On failure this code will silently continue the extraction with `description` set to `None`. That is useful for metafields that may or may not be present.
338
339
340 Another thing to remember is not to try to iterate over `None`
341
342 Say you extracted a list of thumbnails into `thumbnail_data` using `try_get` and now want to iterate over them
343
344 ```python
345 thumbnail_data = try_get(...)
346 thumbnails = [{
347 'url': item['url']
348 } for item in thumbnail_data or []] # correct
349 ```
350
351 and not like:
352
353 ```python
354 thumbnail_data = try_get(...)
355 thumbnails = [{
356 'url': item['url']
357 } for item in thumbnail_data] # incorrect
358 ```
359
360 In the later case, `thumbnail_data` will be `None` if the field was not found and this will cause the loop `for item in thumbnail_data` to raise a fatal error. Using `for item in thumbnail_data or []` avoids this error and results in setting an empty list in `thumbnails` instead.
361
362
363 ### Provide fallbacks
364
365 When extracting metadata try to do so from multiple sources. For example if `title` is present in several places, try extracting from at least some of them. This makes it more future-proof in case some of the sources become unavailable.
366
367
368 #### Example
369
370 Say `meta` from the previous example has a `title` and you are about to extract it. Since `title` is a mandatory meta field you should end up with something like:
371
372 ```python
373 title = meta['title']
374 ```
375
376 If `title` disappears from `meta` in future due to some changes on the hoster's side the extraction would fail since `title` is mandatory. That's expected.
377
378 Assume that you have some another source you can extract `title` from, for example `og:title` HTML meta of a `webpage`. In this case you can provide a fallback scenario:
379
380 ```python
381 title = meta.get('title') or self._og_search_title(webpage)
382 ```
383
384 This code will try to extract from `meta` first and if it fails it will try extracting `og:title` from a `webpage`.
385
386
387 ### Regular expressions
388
389 #### Don't capture groups you don't use
390
391 Capturing group must be an indication that it's used somewhere in the code. Any group that is not used must be non capturing.
392
393 ##### Example
394
395 Don't capture id attribute name here since you can't use it for anything anyway.
396
397 Correct:
398
399 ```python
400 r'(?:id|ID)=(?P<id>\d+)'
401 ```
402
403 Incorrect:
404 ```python
405 r'(id|ID)=(?P<id>\d+)'
406 ```
407
408 #### Make regular expressions relaxed and flexible
409
410 When using regular expressions try to write them fuzzy, relaxed and flexible, skipping insignificant parts that are more likely to change, allowing both single and double quotes for quoted values and so on.
411
412 ##### Example
413
414 Say you need to extract `title` from the following HTML code:
415
416 ```html
417 <span style="position: absolute; left: 910px; width: 90px; float: right; z-index: 9999;" class="title">some fancy title</span>
418 ```
419
420 The code for that task should look similar to:
421
422 ```python
423 title = self._search_regex( # correct
424 r'<span[^>]+class="title"[^>]*>([^<]+)', webpage, 'title')
425 ```
426
427 Or even better:
428
429 ```python
430 title = self._search_regex( # correct
431 r'<span[^>]+class=(["\'])title\1[^>]*>(?P<title>[^<]+)',
432 webpage, 'title', group='title')
433 ```
434
435 Note how you tolerate potential changes in the `style` attribute's value or switch from using double quotes to single for `class` attribute:
436
437 The code definitely should not look like:
438
439 ```python
440 title = self._search_regex( # incorrect
441 r'<span style="position: absolute; left: 910px; width: 90px; float: right; z-index: 9999;" class="title">(.*?)</span>',
442 webpage, 'title', group='title')
443 ```
444
445 or even
446
447 ```python
448 title = self._search_regex( # incorrect
449 r'<span style=".*?" class="title">(.*?)</span>',
450 webpage, 'title', group='title')
451 ```
452
453 Here the presence or absence of other attributes including `style` is irrelevent for the data we need, and so the regex must not depend on it
454
455
456 ### Long lines policy
457
458 There is a soft limit to keep lines of code under 100 characters long. This means it should be respected if possible and if it does not make readability and code maintenance worse. Sometimes, it may be reasonable to go upto 120 characters and sometimes even 80 can be unreadable. Keep in mind that this is not a hard limit and is just one of many tools to make the code more readable.
459
460 For example, you should **never** split long string literals like URLs or some other often copied entities over multiple lines to fit this limit:
461
462 Conversely, don't unecessarily split small lines further. As a rule of thumb, if removing the line split keeps the code under 80 characters, it should be a single line.
463
464 ##### Examples
465
466 Correct:
467
468 ```python
469 'https://www.youtube.com/watch?v=FqZTN594JQw&list=PLMYEtVRpaqY00V9W81Cwmzp6N6vZqfUKD4'
470 ```
471
472 Incorrect:
473
474 ```python
475 'https://www.youtube.com/watch?v=FqZTN594JQw&list='
476 'PLMYEtVRpaqY00V9W81Cwmzp6N6vZqfUKD4'
477 ```
478
479 Correct:
480
481 ```python
482 uploader = traverse_obj(info, ('uploader', 'name'), ('author', 'fullname'))
483 ```
484
485 Incorrect:
486
487 ```python
488 uploader = traverse_obj(
489 info,
490 ('uploader', 'name'),
491 ('author', 'fullname'))
492 ```
493
494 Correct:
495
496 ```python
497 formats = self._extract_m3u8_formats(
498 m3u8_url, video_id, 'mp4', 'm3u8_native', m3u8_id='hls',
499 note='Downloading HD m3u8 information', errnote='Unable to download HD m3u8 information')
500 ```
501
502 Incorrect:
503
504 ```python
505 formats = self._extract_m3u8_formats(m3u8_url,
506 video_id,
507 'mp4',
508 'm3u8_native',
509 m3u8_id='hls',
510 note='Downloading HD m3u8 information',
511 errnote='Unable to download HD m3u8 information')
512 ```
513
514
515 ### Quotes
516
517 Always use single quotes for strings (even if the string has `'`) and double quotes for docstrings. Use `'''` only for multi-line strings. An exception can be made if a string has multiple single quotes in it and escaping makes it significantly harder to read. For f-strings, use you can use double quotes on the inside. But avoid f-strings that have too many quotes inside.
518
519
520 ### Inline values
521
522 Extracting variables is acceptable for reducing code duplication and improving readability of complex expressions. However, you should avoid extracting variables used only once and moving them to opposite parts of the extractor file, which makes reading the linear flow difficult.
523
524 #### Example
525
526 Correct:
527
528 ```python
529 title = self._html_search_regex(r'<title>([^<]+)</title>', webpage, 'title')
530 ```
531
532 Incorrect:
533
534 ```python
535 TITLE_RE = r'<title>([^<]+)</title>'
536 # ...some lines of code...
537 title = self._html_search_regex(TITLE_RE, webpage, 'title')
538 ```
539
540
541 ### Collapse fallbacks
542
543 Multiple fallback values can quickly become unwieldy. Collapse multiple fallback values into a single expression via a list of patterns.
544
545 #### Example
546
547 Good:
548
549 ```python
550 description = self._html_search_meta(
551 ['og:description', 'description', 'twitter:description'],
552 webpage, 'description', default=None)
553 ```
554
555 Unwieldy:
556
557 ```python
558 description = (
559 self._og_search_description(webpage, default=None)
560 or self._html_search_meta('description', webpage, default=None)
561 or self._html_search_meta('twitter:description', webpage, default=None))
562 ```
563
564 Methods supporting list of patterns are: `_search_regex`, `_html_search_regex`, `_og_search_property`, `_html_search_meta`.
565
566
567 ### Trailing parentheses
568
569 Always move trailing parentheses used for grouping/functions after the last argument. On the other hand, literal list/tuple/dict/set should closed be in a new line. Generators and list/dict comprehensions may use either style
570
571 #### Examples
572
573 Correct:
574
575 ```python
576 url = try_get(
577 info,
578 lambda x: x['ResultSet']['Result'][0]['VideoUrlSet']['VideoUrl'],
579 list)
580 ```
581 Correct:
582
583 ```python
584 url = try_get(info,
585 lambda x: x['ResultSet']['Result'][0]['VideoUrlSet']['VideoUrl'],
586 list)
587 ```
588
589 Incorrect:
590
591 ```python
592 url = try_get(
593 info,
594 lambda x: x['ResultSet']['Result'][0]['VideoUrlSet']['VideoUrl'],
595 list,
596 )
597 ```
598
599 Correct:
600
601 ```python
602 f = {
603 'url': url,
604 'format_id': format_id,
605 }
606 ```
607
608 Incorrect:
609
610 ```python
611 f = {'url': url,
612 'format_id': format_id}
613 ```
614
615 Correct:
616
617 ```python
618 formats = [process_formats(f) for f in format_data
619 if f.get('type') in ('hls', 'dash', 'direct') and f.get('downloadable')]
620 ```
621
622 Correct:
623
624 ```python
625 formats = [
626 process_formats(f) for f in format_data
627 if f.get('type') in ('hls', 'dash', 'direct') and f.get('downloadable')
628 ]
629 ```
630
631
632 ### Use convenience conversion and parsing functions
633
634 Wrap all extracted numeric data into safe functions from [`yt_dlp/utils.py`](yt_dlp/utils.py): `int_or_none`, `float_or_none`. Use them for string to number conversions as well.
635
636 Use `url_or_none` for safe URL processing.
637
638 Use `try_get`, `dict_get` and `traverse_obj` for safe metadata extraction from parsed JSON.
639
640 Use `unified_strdate` for uniform `upload_date` or any `YYYYMMDD` meta field extraction, `unified_timestamp` for uniform `timestamp` extraction, `parse_filesize` for `filesize` extraction, `parse_count` for count meta fields extraction, `parse_resolution`, `parse_duration` for `duration` extraction, `parse_age_limit` for `age_limit` extraction.
641
642 Explore [`yt_dlp/utils.py`](yt_dlp/utils.py) for more useful convenience functions.
643
644 #### More examples
645
646 ##### Safely extract optional description from parsed JSON
647 ```python
648 description = traverse_obj(response, ('result', 'video', 'summary'), expected_type=str)
649 ```
650
651 ##### Safely extract more optional metadata
652 ```python
653 video = traverse_obj(response, ('result', 'video', 0), default={}, expected_type=dict)
654 description = video.get('summary')
655 duration = float_or_none(video.get('durationMs'), scale=1000)
656 view_count = int_or_none(video.get('views'))
657 ```
658
659
660
661
662 # EMBEDDING YT-DLP
663 See [README.md#embedding-yt-dlp](README.md#embedding-yt-dlp) for instructions on how to embed yt-dlp in another Python program