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BUG guess_Datetime_format doesn't guess 27.03.2003 14:55:00.000 #50319

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Merged
merged 2 commits into from
Dec 22, 2022
Merged

BUG guess_Datetime_format doesn't guess 27.03.2003 14:55:00.000 #50319

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3aa9d23
fix parsing
Dec 17, 2022
b2f5bf3
stricter regex
Dec 17, 2022
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4 changes: 3 additions & 1 deletion pandas/_libs/tslibs/parsing.pyx
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Original file line number Diff line number Diff line change
Expand Up @@ -1016,9 +1016,11 @@ def guess_datetime_format(dt_str: str, bint dayfirst=False) -> str | None:

cdef str _fill_token(token: str, padding: int):
cdef str token_filled
if "." not in token:
if re.search(r"\d*\.\d+", token) is None:
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is the leading \d* needed here?

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\d+ would be better actually, thanks

This is for when it corresponds with the %S.%f directive

# For example: 98
token_filled = token.zfill(padding)
else:
# For example: 00.123
seconds, nanoseconds = token.split(".")
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is there a risk that this raises if there is a "." but not the regex?

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yup, you'd get

In [6]: token = '.'

In [7]: seconds, nanoseconds = token.split(".")

In [8]: seconds = f"{int(seconds):02d}"
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In [8], line 1
----> 1 seconds = f"{int(seconds):02d}"

ValueError: invalid literal for int() with base 10: ''

which is what happens in the string in the linked issue ('27.03.2003 14:55:00.000')

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i take it this is caught elsewhere so isnt a problem?

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yeah, if the padding was 2 (say) then '.'.zfill(2) would give '0.', and in

pandas/pandas/_libs/tslibs/parsing.pyx

Lines 945 to 946 in f7979be

token_filled = _fill_token(tokens[i], padding)
if token_format is None and token_filled == parsed_formatted:

it wouldn't match parsed_formatted

seconds = f"{int(seconds):02d}"
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@MarcoGorelli MarcoGorelli Dec 17, 2022 •
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previously,

seconds = f"{int(seconds):02d}"

was failing if token was just a single character '.'

If we make the check more precise, then we avoid that issue

# right-pad so we get nanoseconds, then only take
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1 change: 1 addition & 0 deletions pandas/tests/tslibs/test_parsing.py
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Expand Up @@ -179,6 +179,7 @@ def test_parsers_month_freq(date_str, expected):
("2011-12-30 00:00:00.000000", "%Y-%m-%d %H:%M:%S.%f"),
("Tue 24 Aug 2021 01:30:48 AM", "%a %d %b %Y %H:%M:%S %p"),
("Tuesday 24 Aug 2021 01:30:48 AM", "%A %d %b %Y %H:%M:%S %p"),
("27.03.2003 14:55:00.000", "%d.%m.%Y %H:%M:%S.%f"), # GH50317
],
)
def test_guess_datetime_format_with_parseable_formats(string, fmt):
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