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add note about microsecond precision in Calendar.strftime #14137

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Merged
merged 3 commits into from
Jan 4, 2025
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add note about microsecond precision in Calendar.strftime #14137

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0572bef
add note about microsecond precision in Calendar.strftime
simonmcconnell Jan 2, 2025
9e9a6a4
explain in more detail and add examples
simonmcconnell Jan 2, 2025
fa205fd
move microseconds examples to the end
simonmcconnell Jan 4, 2025
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54 changes: 27 additions & 27 deletions lib/elixir/lib/calendar.ex
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Expand Up @@ -496,33 +496,33 @@ defmodule Calendar do

The accepted formats for `string_format` are:

Format | Description | Examples (in ISO)
:----- | :-----------------------------------------------------------------------| :------------------------
a | Abbreviated name of day | Mon
A | Full name of day | Monday
b | Abbreviated month name | Jan
B | Full month name | January
c | Preferred date+time representation | 2018-10-17 12:34:56
d | Day of the month | 01, 31
f | Microseconds *(does not support width and padding modifiers)* | 000000, 999999, 0123
H | Hour using a 24-hour clock | 00, 23
I | Hour using a 12-hour clock | 01, 12
j | Day of the year | 001, 366
m | Month | 01, 12
M | Minute | 00, 59
p | "AM" or "PM" (noon is "PM", midnight as "AM") | AM, PM
P | "am" or "pm" (noon is "pm", midnight as "am") | am, pm
q | Quarter | 1, 2, 3, 4
s | Number of seconds since the Epoch, 1970-01-01 00:00:00+0000 (UTC) | 1565888877
S | Second | 00, 59, 60
u | Day of the week | 1 (Monday), 7 (Sunday)
x | Preferred date (without time) representation | 2018-10-17
X | Preferred time (without date) representation | 12:34:56
y | Year as 2-digits | 01, 01, 86, 18
Y | Year | -0001, 0001, 1986
z | +hhmm/-hhmm time zone offset from UTC (empty string if naive) | +0300, -0530
Z | Time zone abbreviation (empty string if naive) | CET, BRST
% | Literal "%" character | %
Format | Description | Examples (in ISO)
:----- | :-------------------------------------------------------------------------------------------------------- | :------------------------
a | Abbreviated name of day | Mon
A | Full name of day | Monday
b | Abbreviated month name | Jan
B | Full month name | January
c | Preferred date+time representation | 2018-10-17 12:34:56
d | Day of the month | 01, 31
f | Microseconds (truncated to the microsecond precision, but *does not support width and padding modifiers*) | 000000, 999999, 0123
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@josevalim josevalim Jan 2, 2025

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Can you please expand exactly what this means? We cannot have higher precision than microseconds for calendar types, so saying it is truncated is in a way correct, but not because of formatting. Thank you.

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@simonmcconnell simonmcconnell Jan 2, 2025

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If microseconds has precision 6, it prints 6 digits. If it is 3 it prints 3, i.e. milliseconds. I'll add a better explanation when I'm back at the computer.

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@josevalim josevalim Jan 2, 2025

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What if we say: "(always uses its precision for width/padding)"? Then below we can add a line or paragraph with more information :)

H | Hour using a 24-hour clock | 00, 23
I | Hour using a 12-hour clock | 01, 12
j | Day of the year | 001, 366
m | Month | 01, 12
M | Minute | 00, 59
p | "AM" or "PM" (noon is "PM", midnight as "AM") | AM, PM
P | "am" or "pm" (noon is "pm", midnight as "am") | am, pm
q | Quarter | 1, 2, 3, 4
s | Number of seconds since the Epoch, 1970-01-01 00:00:00+0000 (UTC) | 1565888877
S | Second | 00, 59, 60
u | Day of the week | 1 (Monday), 7 (Sunday)
x | Preferred date (without time) representation | 2018-10-17
X | Preferred time (without date) representation | 12:34:56
y | Year as 2-digits | 01, 01, 86, 18
Y | Year | -0001, 0001, 1986
z | +hhmm/-hhmm time zone offset from UTC (empty string if naive) | +0300, -0530
Z | Time zone abbreviation (empty string if naive) | CET, BRST
% | Literal "%" character | %

Any other character will be interpreted as an invalid format and raise an error.

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