Using "--no-cache-dir" flag in pip install ,make sure dowloaded packages
by pip don't cached on system . This is a best practise which make sure
to fetch ftom repo instead of using local cached one . Further , in case
of Docker Containers , by restricing caching , we can reduce image size.
In term of stats , it depends upon the number of python packages
multiplied by their respective size . e.g for heavy packages with a lot
of dependencies it reduce a lot by don't caching pip packages.
Further , more detail information can be found at
https://medium.com/sciforce/strategies-of-docker-images-optimization-2ca9cc5719b6
Signed-off-by: Pratik Raj <rajpratik71@gmail.com>
So using filters like `beautify` won't result in the following error:
```
Traceback (most recent call last):
File "/usr/lib/python3.8/site-packages/urlwatch/handler.py", line 120, in process
data = FilterBase.process(filter_kind, subfilter, self, data)
File "/usr/lib/python3.8/site-packages/urlwatch/filters.py", line 180, in process
return filtercls(state.job, state).filter(data, subfilter)
File "/usr/lib/python3.8/site-packages/urlwatch/filters.py", line 276, in filter
raise ImportError('Please install BeautifulSoup')
ImportError: Please install BeautifulSoup
```
