GH1169 Improve parameter types for DataFrame.pct_change and Series.pct_change

[yangdanny97]

This PR does the following for the two functions in the title:

• replace kwargs with keyword-only parameters for pct_change based on parameters from shift

• replace ... w/ simple defaults when applicable based on docs: https://pandas.pydata.org/docs/reference/api/pandas.Series.pct_change.html

• make fill_method for Series.pct_change be None, just like DataFrame.pct_change since all other values are deprecated

• Closes type kwargs in pct_change according to params in shift #1169

• Tests added: Please use assert_type() to assert the type of any return value

cc @MarcoGorelli should these have tests? they're not overloaded so I'm not sure if it's necessary

[Dr-Irv]

Can you also add tests for the various arguments in test_frame.py:test_dataframe_pct_change() ?

[Dr-Irv]

can you also add tests for Series.pct_change() in test_series.py ?

Use the check(assert_type(... pattern

[yangdanny97]

I had to change the return type of Series.pct_change to get the tests to pass, I don't think the result always has the same dtype as the input.

Based on the docs, the output seems to be a series of floats, but shift is typed with UnknownSeries as the return so maybe this one should also be UnknownSeries...

@Dr-Irv thoughts?

[Dr-Irv]

thanks @yangdanny97

[Dr-Irv]

I had to change the return type of Series.pct_change to get the tests to pass, I don't think the result always has the same dtype as the input.

Based on the docs, the output seems to be a series of floats, but shift is typed with UnknownSeries as the return so maybe this one should also be UnknownSeries...

@Dr-Irv thoughts?

You did the right thing. Series.pct_change() will return a Series[float], so I'm good with that. The previous declaration was just wrong, and existed from when we first created the repo.