Erratic errors downloading metadata

[DNSB]

Since updating to calibre 5.0.1, I'm having issues with metadata downloads being very hit and miss with the "Failed to find any books that match your search" popup and then getting valid metadata on the next attempt.

Spoiler:

calibre, version 5.0.1
ERROR: No matches found: <p>Failed to find any books that match your search. Try making the search <b>less specific</b>. For example, use only the author's last name and a single distinctive word from the title.<p>To see the full log, click "Show details".

Running identify query with parameters: 
{'title': "What's Left of My World", 'authors': ['C. A. Rudolph'], 'identifiers': {'amazon': 'B01N6I0TEU', 'mobi-asin': 'B01N6I0TEU'}, 'timeout': 30} 
Using plugins: Kobo Books (1, 8, 0), Amazon.com (1, 2, 14) 
The log from individual plugins is below 

****************************** Kobo Books (1, 8, 0) ****************************** 
Found 0 results 
Downloading from Kobo Books took 2.9347193241119385 
identify - title: "What's Left of My World" authors= "['C. A. Rudolph']"
create_query - title: "What's Left of My World"
create_query - after decode title: "What's Left of My World"
create_query - title_tokens: "["What's", 'Left', 'of', 'My', 'World']"
Querying: https://www.kobo.com/search?Query=What%27s+Left+of+My+World+Rudolph&fcmedia=Book&fclanguages=all
failed using three divs
Have close enough match - title='The Closets of My Mind', id='the-closets-of-my-mind-1'
failed using three divs
Have close enough match - title='On My Mind . . . Or What's Left Of It', id='on-my-mind-or-what-s-left-of-it'
failed using three divs
Have close enough match - title='What's Left of the World', id='what-s-left-of-the-world'
failed using three divs
Have close enough match - title='What's Left of Her', id='what-s-left-of-her'
failed using three divs
Have close enough match - title='What's Left of Us (What's Left of Me #2)', id='what-s-left-of-us-what-s-left-of-me-2'
KoboBooks url: 'https://www.kobo.com/ebook/the-closets-of-my-mind-1'
KoboBooks url: 'https://www.kobo.com/ebook/on-my-mind-or-what-s-left-of-it'
KoboBooks url: 'https://www.kobo.com/ebook/what-s-left-of-the-world'
KoboBooks url: 'https://www.kobo.com/ebook/what-s-left-of-her'
KoboBooks url: 'https://www.kobo.com/ebook/what-s-left-of-us-what-s-left-of-me-2'
parse_authors - author: "Rosemary Adams"
parse_authors - authors: "['Rosemary Adams']"
Rejecting authors as not a close match:  Rosemary Adams
Could not find title/authors/KoboBooks id for 'https://www.kobo.com/ebook/the-closets-of-my-mind-1'
Kobo Books: 'the-closets-of-my-mind-1' Title: 'The Closets of My Mind' Authors: None
parse_authors - author: "David J. Blacker"
parse_authors - authors: "['David J. Blacker']"
Rejecting authors as not a close match:  David J. Blacker
Could not find title/authors/KoboBooks id for 'https://www.kobo.com/ebook/what-s-left-of-the-world'
Kobo Books: 'what-s-left-of-the-world' Title: "What's Left of the World" Authors: None
parse_authors - author: "Maureen Burns"
parse_authors - authors: "['Maureen Burns']"
Rejecting authors as not a close match:  Maureen Burns
Could not find title/authors/KoboBooks id for 'https://www.kobo.com/ebook/on-my-mind-or-what-s-left-of-it'
Kobo Books: 'on-my-mind-or-what-s-left-of-it' Title: "On My Mind . . . Or What's Left Of It" Authors: None
parse_authors - author: "Amanda Maxlyn"
parse_authors - authors: "['Amanda Maxlyn']"
Rejecting authors as not a close match:  Amanda Maxlyn
Could not find title/authors/KoboBooks id for 'https://www.kobo.com/ebook/what-s-left-of-us-what-s-left-of-me-2'
Kobo Books: 'what-s-left-of-us-what-s-left-of-me-2' Title: "What's Left of Us (What's Left of Me #2)" Authors: None
parse_authors - author: "Mary Campisi"
parse_authors - authors: "['Mary Campisi']"
Rejecting authors as not a close match:  Mary Campisi
Could not find title/authors/KoboBooks id for 'https://www.kobo.com/ebook/what-s-left-of-her'
Kobo Books: 'what-s-left-of-her' Title: "What's Left of Her" Authors: None 

******************************************************************************** 

****************************** Amazon.com (1, 2, 14) ****************************** 
Found 0 results 
Downloading from Amazon.com took 0.0020360946655273438 
Plugin Amazon.com failed
Traceback (most recent call last):
  File "site-packages\calibre\ebooks\metadata\sources\identify.py", line 47, in run
  File "site-packages\calibre\ebooks\metadata\sources\amazon.py", line 1406, in identify
  File "site-packages\calibre\ebooks\metadata\sources\amazon.py", line 995, in browser
  File "site-packages\calibre\__init__.py", line 311, in browser
ImportError: cannot import name 'Browser' from 'calibre.utils.browser' (C:\Program Files\Calibre2\\app\pylib.zip\calibre\utils\browser.pyc) 

******************************************************************************** 
The identify phase took 3.06 seconds 
The longest time (2.934719) was taken by: Kobo Books 
Merging results from different sources 
We have 0 merged results, merging took: 0.00 seconds

I've tried disabling most of the metadata sources I use and that doesn't seem to make any difference. I did notice the error in the Amazon plugin about an ImportError is consistent when the download fails.

[jhowell]

I wonder if the problem is related to this issue with Python 3: Add a bug reference for import not being thread safe

[kovidgoyal]

Yes, it is that issue and I am actually in the middle of fixing it comprehensively by writing my own replacement for python's buggy zipimport module (see the freeze branch). Its a lot of work, so probably the fix will be available only in a week or two.

[kovidgoyal]

And in the meantime this should take care of this particular error:

https://github.com/kovidgoyal/calibr...a04ad7112c6e82

[DNSB]

Thanks for the quick fix.