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[README.md] Add more guide lines for regular expressions

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Sergey M 2019-01-01 23:13:39 +07:00 committed by GitHub
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@ -1133,11 +1133,33 @@ 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
#### Example
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
Say you need to extract `title` from the following HTML code: