[YoutubeDL] Add negation support for string comparisons in format selection expressio...

[youtube-dl] / README.md

diff --git a/README.md b/README.md
index b3c39bf66ccf9f64785928919f8598f108b49bc6..886696015a8b027c8ccac81d384e0613ab603296 100644 (file)
--- a/README.md
+++ b/README.md
@@ -496,7 +496,7 @@ The `-o` option allows users to indicate a template for the output file names.
 
 **tl;dr:** [navigate me to examples](#output-template-examples).
 
-The basic usage is not to set any template arguments when downloading a single file, like in `youtube-dl -o funny_video.flv "https://some/video"`. However, it may contain special sequences that will be replaced when downloading each video. The special sequences may be formatted according to [python string formatting operations](https://docs.python.org/2/library/stdtypes.html#string-formatting). For example, `%(NAME)s` or `%(NAME)05d`. To clarify, that is a percent symbol followed by a name in parentheses, followed by a formatting operations. Allowed names along with sequence type are:
+The basic usage is not to set any template arguments when downloading a single file, like in `youtube-dl -o funny_video.flv "https://some/video"`. However, it may contain special sequences that will be replaced when downloading each video. The special sequences may be formatted according to [python string formatting operations](https://docs.python.org/2/library/stdtypes.html#string-formatting). For example, `%(NAME)s` or `%(NAME)05d`. To clarify, that is a percent symbol followed by a name in parentheses, followed by formatting operations. Allowed names along with sequence type are:
 
  - `id` (string): Video identifier
  - `title` (string): Video title
@@ -667,13 +667,14 @@ The following numeric meta fields can be used with comparisons `<`, `<=`, `>`, `
  - `asr`: Audio sampling rate in Hertz
  - `fps`: Frame rate
 
-Also filtering work for comparisons `=` (equals), `!=` (not equals), `^=` (begins with), `$=` (ends with), `*=` (contains) and following string meta fields:
+Also filtering work for comparisons `=` (equals), `^=` (starts with), `$=` (ends with), `*=` (contains) and following string meta fields:
  - `ext`: File extension
  - `acodec`: Name of the audio codec in use
  - `vcodec`: Name of the video codec in use
  - `container`: Name of the container format
  - `protocol`: The protocol that will be used for the actual download, lower-case (`http`, `https`, `rtsp`, `rtmp`, `rtmpe`, `mms`, `f4m`, `ism`, `http_dash_segments`, `m3u8`, or `m3u8_native`)
  - `format_id`: A short description of the format
+Any string comparison may be prefixed with negation `!` in order to produce an opposite comparison, e.g. `!*=` (does not contain).
 
 Note that none of the aforementioned meta fields are guaranteed to be present since this solely depends on the metadata obtained by particular extractor, i.e. the metadata offered by the video hoster.
 
@@ -1133,11 +1134,33 @@ title = meta.get('title') or self._og_search_title(webpage)
 
 This code will try to extract from `meta` first and if it fails it will try extracting `og:title` from a `webpage`.
 
-### Make regular expressions flexible
+### Regular expressions
 
-When using regular expressions try to write them fuzzy and flexible.
+#### Don't capture groups you don't use
+
+Capturing group must be an indication that it's used somewhere in the code. Any group that is not used must be non capturing.
+
+##### Example
+
+Don't capture id attribute name here since you can't use it for anything anyway.
+
+Correct:
+
+```python
+r'(?:id|ID)=(?P<id>\d+)'
+```
+
+Incorrect:
+```python
+r'(id|ID)=(?P<id>\d+)'
+```
+
+
+#### Make regular expressions relaxed and flexible
+
+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.
  
-#### Example
+##### Example
 
 Say you need to extract `title` from the following HTML code:
 
@@ -1170,6 +1193,25 @@ title = self._search_regex(
     webpage, 'title', group='title')
 ```
 
+### Long lines policy
+
+There is a soft limit to keep lines of code under 80 characters long. This means it should be respected if possible and if it does not make readability and code maintenance worse.
+
+For example, you should **never** split long string literals like URLs or some other often copied entities over multiple lines to fit this limit:
+
+Correct:
+
+```python
+'https://www.youtube.com/watch?v=FqZTN594JQw&list=PLMYEtVRpaqY00V9W81Cwmzp6N6vZqfUKD4'
+```
+
+Incorrect:
+
+```python
+'https://www.youtube.com/watch?v=FqZTN594JQw&list='
+'PLMYEtVRpaqY00V9W81Cwmzp6N6vZqfUKD4'
+```
+
 ### Use safe conversion functions
 
 Wrap all extracted numeric data into safe functions from [`youtube_dl/utils.py`](https://github.com/rg3/youtube-dl/blob/master/youtube_dl/utils.py): `int_or_none`, `float_or_none`. Use them for string to number conversions as well.