bpo-39610: Raise TypeError for len(memoryview_0d)

[eric-wieser]

This makes memoryview.__len__ consistent with memoryview.__getitem__.

https://bugs.python.org/issue39610

(#83791)

[codecov[bot]]

Codecov Report

Merging #18463 into master will increase coverage by 0.02%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18463      +/-   ##
==========================================
+ Coverage   82.11%   82.13%   +0.02%     
==========================================
  Files        1955     1955              
  Lines      588958   584775    -4183     
  Branches    44428    44488      +60     
==========================================
- Hits       483632   480330    -3302     
+ Misses      95677    94794     -883     
- Partials     9649     9651       +2     

Impacted Files	Coverage Δ
Lib/distutils/tests/test_bdist_rpm.py	30.00% <0.00%> (-65.00%)	:arrow_down:
Lib/distutils/command/bdist_rpm.py	7.63% <0.00%> (-56.88%)	:arrow_down:
Modules/_decimal/libmpdec/umodarith.h	80.76% <0.00%> (-19.24%)	:arrow_down:
Lib/test/test_urllib2net.py	76.92% <0.00%> (-13.85%)	:arrow_down:
Lib/test/test_smtpnet.py	78.57% <0.00%> (-7.15%)	:arrow_down:
Lib/ftplib.py	63.85% <0.00%> (-6.06%)	:arrow_down:
Lib/test/test_ftplib.py	87.11% <0.00%> (-4.72%)	:arrow_down:
Tools/scripts/db2pickle.py	17.82% <0.00%> (-3.97%)	:arrow_down:
Tools/scripts/pickle2db.py	16.98% <0.00%> (-3.78%)	:arrow_down:
Lib/test/test_socket.py	71.94% <0.00%> (-3.77%)	:arrow_down:
... and 399 more

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[cpython-cla-bot[bot]]

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[eric-wieser]

@mdickinson: any chance you're willing to review one more buffer-related PR? This one isn't quite as old as the other two of mine you rescued, but it's getting close!

[eric-wieser]

I'm afraid I don't remember what I considered at the time (which is obviously a lesson in writing better commit messages). I'll see if I can come up with an argument either way.

[eric-wieser]

I suspect consistency with numpy was the main argument; along with consistency with to_list:

>>> import numpy as np
>>> arr_0d = np.array(42)
>>> mem_0d = memoryview(arr_0d)

>>> len(arr_0d)
TypeError: len() of unsized object
>>> len(mem_0d.tolist())
TypeError: object of type 'int' has no len()
>>> len(mem_0d)
TypeError: 0-dim memory has no length  # with this PR