cleanup; use timedelta instead of relativedelta where possible

[jbrockmendel]

• Cleanup, flake8, modernize imports
• Replace usage of other + relativedelta(...) with other + timedelta(...) or other.replace(...) where possible. Clearer and more performant.
• Use _get_firstbday in one place that had previously duplicated its logic.

asv continuous -f 1.1 -E virtualenv master HEAD -b timeseries [...] before after ratio [8dac6331] [c6145385] - 31.4±0.2μs 26.7±0.3μs 0.85 timeseries.Offsets.time_custom_bday_decr - 14.4±0.1ms 12.0±0.2ms 0.84 timeseries.DatetimeIndex.time_infer_freq_none - 1.76s 1.45s 0.82 timeseries.Iteration.time_iter_periodindex - 53.8±0.2μs 42.2±0.2μs 0.78 timeseries.SemiMonthOffset.time_end_decr_n - 53.1±4μs 41.1±0.3μs 0.78 timeseries.SemiMonthOffset.time_begin_incr_n - 54.6±0.2μs 41.5±0.2μs 0.76 timeseries.SemiMonthOffset.time_begin_decr_n - 3.55±0.5ms 2.70±0.01ms 0.76 timeseries.ToDatetime.time_iso8601_nosep - 51.8±0.2μs 38.6±0.2μs 0.75 timeseries.SemiMonthOffset.time_begin_decr - 53.0±3μs 38.1±0.3μs 0.72 timeseries.SemiMonthOffset.time_end_incr_n - 47.5±0.3μs 34.0±0.3μs 0.72 timeseries.SemiMonthOffset.time_end_incr - 49.2±0.2μs 34.9±0.8μs 0.71 timeseries.SemiMonthOffset.time_begin_incr - 55.8±0.1μs 39.3±1μs 0.70 timeseries.SemiMonthOffset.time_end_decr - 43.6±0.5μs 30.7±0.2μs 0.70 timeseries.SemiMonthOffset.time_begin_apply - 43.6±0.4μs 30.6±0.1μs 0.70 timeseries.SemiMonthOffset.time_end_apply 

[pep8speaks]

Hello @jbrockmendel! Thanks for updating the PR.

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

Comment last updated on November 09, 2017 at 04:50 Hours UTC

[codecov]

Codecov Report

Merging #18183 into master will decrease coverage by 0.01%.
The diff coverage is 92.85%.

@@ Coverage Diff @@ ## master #18183 +/- ## ========================================== - Coverage 91.42% 91.4% -0.02%  ========================================== Files 163 163 Lines 50068 50065 -3 ========================================== - Hits 45776 45764 -12  - Misses 4292 4301 +9

Flag	Coverage Δ
#multiple	89.21% <92.85%> (-0.01%)	⬇️
#single	40.36% <14.28%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
pandas/tseries/offsets.py	97.1% <92.85%> (-0.01%)	⬇️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.8% <0%> (-0.1%)	⬇️

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[codecov]

Codecov Report

Merging #18183 into master will decrease coverage by 0.01%.
The diff coverage is 92.85%.

@@ Coverage Diff @@ ## master #18183 +/- ## ========================================== - Coverage 91.42% 91.4% -0.02%  ========================================== Files 163 163 Lines 50068 50065 -3 ========================================== - Hits 45776 45764 -12  - Misses 4292 4301 +9

Flag	Coverage Δ
#multiple	89.21% <92.85%> (-0.01%)	⬇️
#single	40.36% <14.28%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
pandas/tseries/offsets.py	97.1% <92.85%> (-0.01%)	⬇️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.8% <0%> (-0.1%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #18183 into master will decrease coverage by 0.01%.
The diff coverage is 92.85%.

@@ Coverage Diff @@ ## master #18183 +/- ## ========================================== - Coverage 91.42% 91.4% -0.02%  ========================================== Files 163 163 Lines 50068 50065 -3 ========================================== - Hits 45776 45764 -12  - Misses 4292 4301 +9

Flag	Coverage Δ
#multiple	89.21% <92.85%> (-0.01%)	⬇️
#single	40.36% <14.28%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
pandas/tseries/offsets.py	97.1% <92.85%> (-0.01%)	⬇️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.8% <0%> (-0.1%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[jorisvandenbossche]

Question (it has been a long time I worked with relativedeltas): in the non-replace case (so when using plural kwargs to relativedelta), is addition with relativedelta then always fully equivalent to addition of a timedelta?
Eg there are no differences in how they handle DST changes? (where adding 1 day might actually add 24 hours but change the hour of the result, or keep the hour of the result and thus adds 23/25 hours)

[jreback]

i would leave the weeks, not real well tested for timedelta; relativedelta may be more intelligent here

[jbrockmendel]

i would leave the weeks, not real well tested for timedelta

Not sure I understand. You mean the stdlib timedelta isn't well-tested?

[jbrockmendel]

relativedelta may be more intelligent here

The relativedelta constructor just adds weeks*7 to the days kwarg.

[jbrockmendel]

Question (it has been a long time I worked with relativedeltas):

The fact that relativedelta's behavior is more obscure is part of why this change is helpful. (Also the perf improvement is a free lunch)

in the non-replace case (so when using plural kwargs to relativedelta), is addition with relativedelta then always fully equivalent to addition of a timedelta?

For everything weeks and shorter, yes. Months and years have more complicated behavior.

Eg there are no differences in how they handle DST changes?

In the pertinent case, relativedelta.__add__ passes through to timedelta:

ret = (other.replace(**repl) + datetime.timedelta(days=days, hours=self.hours, minutes=self.minutes, seconds=self.seconds, microseconds=self.microseconds)) 

[jbrockmendel]

Working on fixes for #8386 and a few related things. That should hurt perf very slightly. I'd like to get these perf improvements in so as to stay "in the black". (and to keep the cleanup separate from the non-trivial upcoming diffs)

[jbrockmendel]

Superceded by #18218.