Replace old string formatting syntax with f-strings

[ShaharNaveh]

Since we no longer support python 3.5, we can now use the new f-strings instead of the old .format() ( and obviously the % formatting).

Notes:

• Don't forget to link this issue in your pull request's body message , simply paste this https://github.com/pandas-dev/pandas/issues/29547 in your pull request's body message.

• If any of your changed files are related to Replace "foo!r" to "repr(foo)" syntax #29886 , please make sure to link your pull request to that issue as well, simply paste this https://github.com/pandas-dev/pandas/issues/29886 in your pull request's body message as well.

• Please comment what you are planning to work on, so we won't do double work.

• If a file/files that should be marked as done, is not marked, please comment letting me know.

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To check what files still needs to be fixed in the pandas directory:

grep -l -R '%s'  --include=*.{py,pyx} pandas/
grep -l -R '%d' --include=*.{py,pyx} pandas/
grep -l -R '\.format(' --include=*.{py,pyx} pandas/

All of the above can also be used as a one liner:

grep -l -R -e '%s' -e '%d' -e '\.format(' --include=*.{py,pyx} pandas/

Tip:

If you want to see the line number of the occurrence, replace the -l with -n
for example:

grep -n -R '%s' --include=*.{py,pyx} pandas/

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The current list is:

• pandas/compat/pickle_compat.py

• pandas/_config/config.py

• pandas/core/arrays/datetimelike.py

• pandas/core/arrays/datetimes.py

• pandas/core/arrays/integer.py

• pandas/core/arrays/period.py

• pandas/core/computation/pytables.py

• pandas/core/config_init.py

• pandas/core/frame.py

• pandas/core/generic.py

• pandas/core/groupby/generic.py

• pandas/core/groupby/groupby.py

• pandas/core/indexes/base.py

• pandas/core/indexes/multi.py

• pandas/core/indexes/range.py

• pandas/core/ops/docstrings.py

• pandas/core/ops/__init__.py

• pandas/core/reshape/merge.py

• pandas/core/tools/datetimes.py

• pandas/io/formats/css.py

• pandas/io/formats/excel.py

• pandas/io/formats/format.py

• pandas/io/formats/html.py

• pandas/io/formats/info.py

• pandas/io/formats/latex.py

• pandas/io/formats/printing.py

• pandas/io/formats/style.py

• pandas/io/parsers.py

• pandas/io/pytables.py

• pandas/io/sas/sas_xport.py

• pandas/io/stata.py

• pandas/_libs/tslibs/c_timestamp.pyx

• pandas/_libs/tslibs/frequencies.pyx

• pandas/_libs/tslibs/parsing.pyx

• pandas/_libs/tslibs/period.pyx

• pandas/_libs/tslibs/strptime.pyx

• pandas/_libs/tslibs/timedeltas.pyx

• pandas/plotting/_matplotlib/converter.py

• pandas/tests/arrays/categorical/test_operators.py

• pandas/tests/arrays/test_datetimelike.py

• pandas/tests/dtypes/test_dtypes.py

• pandas/tests/extension/base/setitem.py

• pandas/tests/frame/test_constructors.py

• pandas/tests/frame/test_missing.py

• pandas/tests/frame/test_to_csv.py

• pandas/tests/groupby/aggregate/test_other.py

• pandas/tests/indexes/datetimes/test_date_range.py

• pandas/tests/indexes/datetimes/test_datetime.py

• pandas/tests/indexes/datetimes/test_formats.py

• pandas/tests/indexes/datetimes/test_partial_slicing.py

• pandas/tests/indexes/interval/test_constructors.py

• pandas/tests/indexes/interval/test_interval.py

• pandas/tests/indexes/multi/test_format.py

• pandas/tests/indexes/period/test_formats.py

• pandas/tests/indexes/test_base.py

• pandas/tests/indexes/timedeltas/test_timedelta.py

• pandas/tests/indexing/test_categorical.py

• pandas/tests/indexing/test_coercion.py

• pandas/tests/io/excel/test_openpyxl.py

• pandas/tests/io/excel/test_writers.py

• pandas/tests/io/formats/test_format.py

• pandas/tests/io/formats/test_printing.py

• pandas/tests/io/formats/test_style.py

• pandas/tests/io/formats/test_to_csv.py

• pandas/tests/io/formats/test_to_html.py

• pandas/tests/io/formats/test_to_latex.py

• pandas/tests/io/parser/test_compression.py

• pandas/tests/io/parser/test_encoding.py

• pandas/tests/io/parser/test_header.py

• pandas/tests/io/parser/test_parse_dates.py

• pandas/tests/io/parser/test_usecols.py

• pandas/tests/io/test_html.py

• pandas/tests/io/test_sql.py

• pandas/tests/io/test_stata.py

• pandas/tests/reductions/test_reductions.py

• pandas/tests/reshape/test_concat.py

• pandas/tests/reshape/test_melt.py

• pandas/tests/scalar/period/test_period.py

• pandas/tests/scalar/timedelta/test_timedelta.py

• pandas/tests/scalar/timestamp/test_constructors.py

• pandas/tests/series/indexing/test_numeric.py

• pandas/tests/series/indexing/test_take.py

• pandas/tests/series/indexing/test_where.py

• pandas/tests/series/methods/test_rename.py

• pandas/tests/series/test_api.py

• pandas/tests/series/test_constructors.py

• pandas/tests/series/test_datetime_values.py

• pandas/tests/series/test_repr.py

• pandas/tests/test_strings.py

• pandas/tests/tools/test_to_datetime.py

• pandas/tests/tseries/holiday/test_calendar.py

• pandas/tests/tseries/holiday/test_holiday.py

• pandas/tests/tslibs/test_parsing.py

• pandas/tests/util/test_assert_frame_equal.py

• pandas/tseries/frequencies.py

• pandas/util/_decorators.py

• pandas/util/_test_decorators.py

• pandas/util/_validators.py

• pandas/_version.py

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NOTE:

The list may change as files are moved/renamed constantly.

---

Inhereted files and commands from this PR.

[ShaharNaveh]

Im taking:

• pandas/_libs/groupby.pyx

• pandas/_libs/hashing.pyx

• pandas/_libs/index.pyx

• pandas/_libs/internals.pyx

• pandas/_libs/interval.pyx

• pandas/_libs/lib.pyx

• pandas/_libs/ops.pyx

• pandas/_libs/parsers.pyx

• pandas/_libs/reduction.pyx

• pandas/_libs/sparse.pyx

• pandas/_libs/testing.pyx

• pandas/_libs/tslib.pyx

• pandas/_libs/window.pyx

[yashukla]

I'll take:

• pandas/tests/indexes/test_base.py
• pandas/tests/indexes/test_category.py
• pandas/tests/indexes/test_common.py
• pandas/tests/indexes/test_numeric.py

to start, if that's alright!

[SaturnFromTitan]

Hi @MomIsBestFriend Can you recommend any tools for this conversion? A quick look gave me these:

1. pyupgrade
2. fstringify
3. flynt

I have no experience with either of them, but they could be very helpful here

[ShaharNaveh]

Hello @SaturnFromTitan , I personally sometimes use pyupgrade but only when the file contain only a few outdated string formats in it. Then I look at the changes and fix if pyupgrade got something wrong.

When they're files with alot of occurrences I go for the "complex" ones manually (e.g '%.2f' % my_float) and let it deal with the common ones, usually it gets it right.

Also, some of the changes will make the changed file non pep8 compatible, so there's a need to fix that as well, otherwise it will not pass the tests.