[CONTRIBUTING.md] Add some more coding conventions (#21939)

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Kyle 2019-08-02 06:49:01 +09:00 committed by Sergey M
parent 535111657b
commit 07f3a05c87
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@ -366,3 +366,67 @@ duration = float_or_none(video.get('durationMs'), scale=1000)
view_count = int_or_none(video.get('views'))
```
### Inline values
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.
#### Example
Correct:
```python
title = self._html_search_regex(r'<title>([^<]+)</title>', webpage, 'title')
```
Incorrect:
```python
TITLE_RE = r'<title>([^<]+)</title>'
# ...some lines of code...
title = self._html_search_regex(TITLE_RE, webpage, 'title')
```
### Collapse fallbacks
Multiple fallback values can quickly become unwieldy. Collapse multiple fallback values into a single expression via a list of meta values.
#### Example
Good:
```python
description = self._html_search_meta(
['og:description', 'description', 'twitter:description'],
webpage, 'description', default=None)
```
Unwieldy:
```python
description = (
self._og_search_description(webpage, default=None)
or self._html_search_meta('description', webpage, default=None)
or self._html_search_meta('twitter:description', webpage, default=None))
```
### Trailing parentheses
Always move trailing parentheses after the last argument.
#### Example
Correct:
```python
lambda x: x['ResultSet']['Result'][0]['VideoUrlSet']['VideoUrl'],
list)
```
Incorrect:
```python
lambda x: x['ResultSet']['Result'][0]['VideoUrlSet']['VideoUrl'],
list,
)
```