Fix the stackoverflow problem (Sourcery refactored)

[sourcery-ai]

Pull Request #7 refactored by Sourcery.

Since the original Pull Request was opened as a fork in a contributor's
repository, we are unable to create a Pull Request branching from it.

To incorporate these changes, you can either:

1. Merge this Pull Request instead of the original, or

2. Ask your contributor to locally incorporate these commits and push them to
   the original Pull Request

   Incorporate changes via command line

   git fetch https://github.com/MarcoGorelli/pymc3 pull/7/head
   git merge --ff-only FETCH_HEAD
   git push

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will be closed automatically.

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[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 0.17%.

Quality metrics	Before	After	Change
Complexity	19.10 😞	18.81 😞	-0.29 👍
Method Length	104.44 🙂	104.64 🙂	0.20 👎
Working memory	14.79 😞	14.77 😞	-0.02 👍
Quality	46.16% 😞	46.33% 😞	0.17% 👍

Other metrics	Before	After	Change
Lines	4041	4062	21

Changed files	Quality Before	Quality After	Quality Change
pymc3/memoize.py	68.67% 🙂	67.63% 🙂	-1.04% 👎
pymc3/sampling.py	28.39% 😞	28.37% 😞	-0.02% 👎
pymc3/util.py	69.59% 🙂	70.41% 🙂	0.82% 👍
pymc3/distributions/posterior_predictive.py	34.57% 😞	34.23% 😞	-0.34% 👎
pymc3/tests/test_memo.py	95.00% ⭐	73.57% 🙂	-21.43% 👎
pymc3/tests/test_sampling.py	65.95% 🙂	65.97% 🙂	0.02% 👍

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
pymc3/sampling.py	sample	83 ⛔	883 ⛔	32 ⛔	1.10% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
pymc3/distributions/posterior_predictive.py	_PosteriorPredictiveSampler.draw_value	74 ⛔	496 ⛔	35 ⛔	1.69% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
pymc3/sampling.py	sample_posterior_predictive	40 ⛔	364 ⛔	22 ⛔	10.47% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
pymc3/distributions/posterior_predictive.py	_PosteriorPredictiveSampler.draw_values	40 ⛔	381 ⛔	20 ⛔	11.26% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
pymc3/sampling.py	init_nuts	26 😞	736 ⛔	28 ⛔	12.82% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions

Legend and Explanation

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• ⛔ very poor

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[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (windows-test@73ca256). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff               @@
##             windows-test       #8   +/-   ##
===============================================
  Coverage                ?   87.64%           
===============================================
  Files                   ?       88           
  Lines                   ?    14346           
  Branches                ?        0           
===============================================
  Hits                    ?    12574           
  Misses                  ?     1772           
  Partials                ?        0