Problem with Python f-string formatting of struct_time

Question

I have the following code;

oStat=os.stat(oFile)
print(time.strftime('%H:%M:%S', time.localtime(oStat.st_mtime)))
print(f"{time.localtime(oStat.st_mtime):%H:%M:%S}")

The first print statement works as expected; the f-string gives me:

    print(f"{time.localtime(oStat.st_mtime):%H:%M:%S}")
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unsupported format string passed to time.struct_time.__format__

The desired output should be a time eg:

14:10:02

Why is this in error and how can I fix it?

I've tried various combinations but none work.

The TypeError tells you everything you need to know. What were you hoping the output would look like? — jackal
– jackal, Commented Apr 30, 2024 at 12:58
That type of formatting works on datetime or date objects from the datetime module. The time.localtime function returns a low-level type which doesn't support formatting. — interjay
– interjay, Commented Apr 30, 2024 at 13:00
struct_time just inherits object.__format__, which doesn't support any kind of format modification: it only accepts the empty string as an argument. — chepner
– chepner, Commented Apr 30, 2024 at 13:22
(For f-strings, that means you can provide the : to "introduce" a format specification, but that specification must be empty: f'{time.localtime(...):}' is valid, but nothing more complicated is.) — chepner
– chepner, Commented Apr 30, 2024 at 13:24

interjay · Accepted Answer · 2024-04-30 13:17:13Z

4

The time module's struct_time is low-level and doesn't support formatting with f-strings, requiring a call to time.strftime instead.

You should prefer using the datetime module's high-level types:

from datetime import datetime

oStat=os.stat(oFile)
dt = datetime.fromtimestamp(oStat.st_mtime)
print(f'{dt:%H:%M:%S}')

answered Apr 30, 2024 at 13:17

interjay

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Comments

Theophile · Accepted Answer · 2024-04-30 12:58:40Z

-2

The end of your f-string seems weird.

time.localtime(oStat.st_mtime):%H:%M:%S

This isn't valid python code, what are you trying to output ?

This would be better :

time.strftime('%H:%M:%S', time.localtime(oStat.st_mtime))

answered Apr 30, 2024 at 12:58

Theophile

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2 Comments

Ted Elliott Over a year ago

It is valid inside of an f-string. The part after the first ':' is an optional format string. It could be the multiple occurrences of ':'

interjay Over a year ago

That type of formatting works just fine with datetime objects (even with multiple :). And your suggested solution is already given in the question.

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