Raise exception if downloading a file wasn't possible

[Herob527]

I was thinking:
Why failure of downloading file doesn't raise exception like FileNotAvailable or something like that?

In google colab it doesn't raise this error if download failed.

[wkentaro]

What kind of failure cases are you referring to?

When IOError happens, now it returns None:

gdown/gdown/download.py

Lines 271 to 273 in 1bf9e20

	except IOError as e:
	print(e, file=sys.stderr)
	return

Is this what you're talking about?

[Skitionek]

I believe that would be one of the examples. It seems to follow particularly bad pattern of printing errors and returning none. Therefore it cannot really be used as python library (since it does not provide any feedback to python caller on what actually has happened).

I need to handle permission error and to do so there no other way than forking this code.

[wkentaro]

Closed via #260