DEPR: casting strings to float in to_datetime with unit

[jbrockmendel]

• closes API: to_datetime with unit changes how strings are interpreted #50735 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[mroeschke]

I guess this is okay (+0) although it makes to_datetime a little less convenient.

[MarcoGorelli]

Looks good to me

Reckon the "inverse" should be deprecated as well, i.e. parsing numeric with format as strings, like

In [3]: to_datetime([20200101], format='%Y%m%d')
Out[3]: DatetimeIndex(['2020-01-01'], dtype='datetime64[ns]', freq=None)

?

[MarcoGorelli]

is this just to avoid hitting the warning later in to_datetime(new_data, errors="raise", unit=date_unit), which would be outofbounds anyway?

[jbrockmendel]

correct

[jbrockmendel]

Reckon the "inverse" should be deprecated as well, i.e. parsing numeric with format as strings, like

That definitely seems like a potential footgun, no idea how common that is in the wild.