Pin matplotlib version in requirements.txt or drop usage of hold to avoid AttributeError

[jhadjar]

Summary:

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Running the notebook ipynb/Economics.ipynb raises an AttributeError exception with matplotlib-3.1.3 installed.

Reproduce:

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• Run the notebook with a matplotlib version that deprecated hold

Actual outcome:

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An AttributeError exception is raised.

Expected outcome:

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A sweet notebook running.

Logs &/or traceback:

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Traceback

AttributeError Traceback (most recent call last)

 in 

----> 1 show(population)
 in show(population, k, percentiles, **kwargs)

19     plt.title('/'.join(map(str, percentiles)) + ' Percentile Plots')

20     times = [t for (t, pop) in results]

-->21     plt.hold(True); plt.xlabel('wealth'); plt.ylabel('time'); plt.grid(True)

22     for pct in percentiles:

23         line = [percent(pct, pop) for (t, pop) in results]
AttributeError: module 'matplotlib.pyplot' has no attribute 'hold'

Likely parts and draft fix:

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Change requirements.txt to pin the matplotlib version to something like 2.1.0:

numpy
matplotlib==2.1.0

Another option is to update the code in ipynb/Economics.ipynb to use the updated API.