Revise GrowFactors constructor to handle custom growfactors files

[martinholmer]

Default is still to use baseline growfactors in the package's growfactors.csv file.
Now users of the Python API can specify custom growth factors to be used by the Records object.

For an example of how to use this new Tax-Calculator feature, we this comment.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.42%. Comparing base (e0234b6) to head (afb7df1).
Report is 16 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2757   +/-   ##
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  Coverage   99.42%   99.42%           
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  Files          13       13           
  Lines        2605     2607    +2     
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+ Hits         2590     2592    +2     
  Misses         15       15           

Flag	Coverage Δ
unittests	99.42% <100.00%> (+<0.01%)	⬆️

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Files	Coverage Δ
taxcalc/__init__.py	100.00% <100.00%> (ø)
taxcalc/calculator.py	100.00% <ø> (ø)
taxcalc/growfactors.py	100.00% <100.00%> (ø)
taxcalc/parameters.py	100.00% <ø> (ø)

[donboyd5]

Thanks for this, @martinholmer, it is really helpful.

[martinholmer]

The following Python script illustrates the use of the new feature added in PR #2757:

"""
This gf.py script illustrates use of GrowFactors constructor with custom
growfactors representing a 2020 spike in wage inflation, a feature that
is in Tax-Calculator pull request #2757 and will be included beginning
in the Tax-Calculator 4.0.0 release.

(taxcalc-dev) Tax-Calculator% diff mygf.csv taxcalc/growfactors.csv
11c11
< 2020,1.067957,1.167938,0.947032,1.00799,1.041121,1.116381,1.016054,...
---                                                  ^^
> 2020,1.067957,1.167938,0.947032,1.00799,1.041121,1.006381,1.016054,...

(taxcalc-dev) Tax-Calculator% python gf.py
2112.718 2367.885
"""

from taxcalc import GrowFactors, Policy, Records, Calculator


TAXYEAR = 2022

gf0 = GrowFactors()
gf1 = GrowFactors(growfactors_filename='../Tax-Calculator/mygf.csv')

recs0 = Records('puf.csv', start_year=Records.PUFCSV_YEAR, gfactors=gf0)
recs1 = Records('puf.csv', start_year=Records.PUFCSV_YEAR, gfactors=gf1)

calc0 = Calculator(policy=Policy(), records=recs0)
calc1 = Calculator(policy=Policy(), records=recs1)

calc0.advance_to_year(TAXYEAR)
calc1.advance_to_year(TAXYEAR)

calc0.calc_all()
calc1.calc_all()

itax0 = calc0.weighted_total('iitax')
itax1 = calc1.weighted_total('iitax')

assert itax1 > itax0
print(round(itax0*1e-9, 3), round(itax1*1e-9, 3))

Executing the above script produces these results:

(taxcalc-dev) Tax-Calculator% python gf.py
2112.718 2367.885