Fix attribute error in read_checks function

[GenevieveBuckley]

Closes #11

I tried the first example on the fastdownload README page, using the url of one of the standard fastai datasets available on S3. It raised an attribute error, because variable fmod was an empty dictionary instead of the expected pathlib object.

from fastdownload import FastDownload

url = 'https://s3.amazonaws.com/fast-ai-sample/mnist_tiny.tgz'
d = FastDownload()
path = d.get(url)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-50-389349d26777> in <module>
      3 url = 'https://s3.amazonaws.com/fast-ai-sample/mnist_tiny.tgz'
      4 d = FastDownload()
----> 5 path = d.get(url)

~/anaconda3/envs/napari-dev/lib/python3.9/site-packages/fastdownload/core.py in get(self, url, extract_key, force)
    119             data = self.data_path(extract_key, urldest(url, self.arch_path()))
    120             if data.exists(): return data
--> 121         self.download(url, force=force)
    122         return self.extract(url, extract_key=extract_key, force=force)

~/anaconda3/envs/napari-dev/lib/python3.9/site-packages/fastdownload/core.py in download(self, url, force)
     94         "Download `url` to archive path, unless exists and `self.check` fails and not `force`"
     95         self.arch_path().mkdir(exist_ok=True, parents=True)
---> 96         return download_and_check(url, urldest(url, self.arch_path()), self.module, force)
     97 
     98     def rm(self, url, rm_arch=True, rm_data=True, extract_key='data'):

~/anaconda3/envs/napari-dev/lib/python3.9/site-packages/fastdownload/core.py in download_and_check(url, fpath, fmod, force)
     61     "Download `url` to `fpath`, unless exists and `check` fails and not `force`"
     62     if not force and fpath.exists():
---> 63         if check(fmod, url, fpath): return fpath
     64         else: print("Downloading a new version of this dataset...")
     65     res = download_url(url, fpath)

~/anaconda3/envs/napari-dev/lib/python3.9/site-packages/fastdownload/core.py in check(fmod, url, fpath)
     47 def check(fmod, url, fpath):
     48     "Check whether size and hash of `fpath` matches stored data for `url` or data is missing"
---> 49     checks = read_checks(fmod).get(url)
     50     return not checks or path_stats(fpath)==checks
     51 

~/anaconda3/envs/napari-dev/lib/python3.9/site-packages/fastdownload/core.py in read_checks(fmod)
     40 def read_checks(fmod):
     41     "Evaluated contents of `download_checks.py`"
---> 42     if not fmod.exists(): return {}
     43     txt = fmod.read_text()
     44     return eval(txt) if txt else {}

AttributeError: 'dict' object has no attribute 'exists'

This PR avoids that error, by checking whether fmod is an empty dictionary before continuing.

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[GenevieveBuckley]

I'm not super familiar with nbdev, so if there's anything about the process I should have done differently please let me know.

I looked at both:

• the fastdownload contributing guide, and
• the nbdev tutorial

...but I don't think I had things working properly (for example, running nbdev_test_nbs on the master branch didn't pass cleanly, which might indicate something is wrong with my setup)

[GenevieveBuckley]

Note: I think this is probably unrelated to #16 EDIT: perhaps not, turns out the dropbox zip file I was using to check this has something wrong with it (file seems to be corrupt). Probably worth testing it with a better example file on Dropbox.

[tcapelle]

I have the same issue, can you take a look @jph00

[jph00]

Many thanks @GenevieveBuckley !

[seeM]

@jph00 Just wanted to note that the latest version of fastdownload on PyPI (0.0.5) still has this bug. A new release would be amazing 😄 I'm happy to help where I can.

For interest sake, I'm currently working around it by installing from GitHub (pinned to the latest commit):

pip install git+https://github.com/fastai/fastdownload.git@2ec6563fef7c92ea975871c8cbcea1a0b02917a1

[jph00]

Oh sorry @seeM my bad! Thanks for letting me know. Just pushed a release.

[seeM]

Thank you, very much appreciated. I really love the library! It's such a pleasure to use 😌