Make some attributes of DateOffset read-only; add tests

[jbrockmendel]

This PR takes over for #17137. That PR tried to handle the general case of this issue, but ultimately doing that correctly would require a much more extreme refactoring.

This PR only used a cached version of _params when kwds is empty. This special case covers 'M', 'D', 'H', 'min', 'sec', 'ms', 'us', 'ns' special cases.

I plan to extend this to cover at least the Annual and Quarterly cases, but doing that carefully may take a while, so this can get the ball rolling.

• closes #xxxx
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #17181 into master will decrease coverage by 0.01%.
The diff coverage is 96%.

@@            Coverage Diff             @@
##           master   #17181      +/-   ##
==========================================
- Coverage   90.99%   90.98%   -0.02%     
==========================================
  Files         162      162              
  Lines       49508    49543      +35     
==========================================
+ Hits        45052    45076      +24     
- Misses       4456     4467      +11

Flag	Coverage Δ
#multiple	88.76% <96%> (ø)	⬆️
#single	40.27% <70%> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/tseries/offsets.py	97.06% <96%> (-0.07%)	⬇️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.66% <0%> (-0.1%)	⬇️

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[codecov]

Codecov Report

Merging #17181 into master will decrease coverage by 0.01%.
The diff coverage is 97.22%.

@@            Coverage Diff             @@
##           master   #17181      +/-   ##
==========================================
- Coverage      91%   90.98%   -0.02%     
==========================================
  Files         162      162              
  Lines       49508    49530      +22     
==========================================
+ Hits        45055    45067      +12     
- Misses       4453     4463      +10

Flag	Coverage Δ
#multiple	88.77% <97.22%> (ø)	⬆️
#single	40.27% <88.88%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
pandas/tseries/offsets.py	97.1% <97.22%> (-0.03%)	⬇️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.71% <0%> (-0.1%)	⬇️

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[jreback]

so this needs a deprecation cycle for n & normalize, rather than raising here.

[jbrockmendel]

This PR is not a long-term solution. Instead how about we have it clear the cache whenever an attribute is re-set? That should ensure correctness without breaking backward-compatibility.

[pep8speaks]

Hello @jbrockmendel! Thanks for updating the PR.

Cheers ! There are no PEP8 issues in this Pull Request. 🍻

Comment last updated on August 26, 2017 at 19:25 Hours UTC

[jbrockmendel]

I've got a much better approach that can be implemented if/when #17274 is merged. Closing this to be replaced at a later date.