Issue with cache root

[Narsil]

Describe the bug
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It seems the cache root is wrong if it is defined in the environment instead of the default

To Reproduce
Steps to reproduce the behavior (e.g. which model did you train? what parameters did you use? etc.).

Create test.py:

from flair.data import Sentence
from flair.models import SequenceTagger

# make a sentence
sentence = Sentence('I love Berlin .')

# load the NER tagger
tagger = SequenceTagger.load('ner')

# run NER over sentence
tagger.predict(sentence)

and run
FLAIR_CACHE_ROOT=$HOME/.cache/ python test.py

Expected behavior
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Example should work out of th box

Screenshots
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Environment (please complete the following information):

• OS [e.g. iOS, Linux]: ubuntu
• Version [e.g. flair-0.3.2]: 0.8.1 (or master)

Additional context
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Simple fix is to cast to Path too when coming from env.

[HallerPatrick]

I also looked into this and can reproduce the bug. In this context I searched every occurrence of flair.cache_root, which holds the env value. And every time it is used to construct a Path object.

What I therefore would propose is to initially construct the Path object in the flair/__init__.py and remove every other construction of it in the source code.

Otherwise only a Path construction in flair/models/sequence_tagger.py has to be added.

I could do a PR for both.

Note: There are 237 occurrences of Path(flair.cache_root)

[alanakbik]

@HallerPatrick thanks for looking into this - a PR would be great! I guess it would be easier to construct it once in the init.

[HallerPatrick]

This can be closed :)