Python datetime: convert milliseconds to string, preserving zeroes

Question

I'd like to convert a number of milliseconds to a formatted string using Python's datetime.

def milliseconds_to_str(t):
     """Converts the number of milliseconds to HH:MM:SS,ms time"""
     return str(datetime.timedelta(milliseconds=t)).replace('.', ',')[:-3]

The above works extremely well, for example:

> milliseconds_to_str(8712313): '2:25:12,313'

The problem arises when the number of milliseconds is an even multiple of 1000, for example:

milliseconds_to_srt_time(1000) > 0:00 (Should be 0:00:01,000)
milliseconds_to_srt_time(1000000) > 0:16 (Should be 0:16:00,000)
milliseconds_to_srt_time(4000400) > 1:06:40,400 (GOOD)
milliseconds_to_srt_time(80808231) > 22:26:48,231 (GOOD)
milliseconds_to_srt_time(80808000) > 22:26 (Should be 22:26:00,000)

How can I avoid this rounding?

related: [format timedelta to string](https://stackoverflow.com/questions/538666/format-timedelta-to-string) — FObersteiner, Sep 21 '21 at 06:29

score 1 · Answer 1 · answered Sep 21 '21 at 03:17

Using a fixed slicing of [:-3] wouldn't work because the resulting string of the milliseconds varies.

2:25:12.313000
0:00:01

Here, it will only be applicable to the 1st (where the last 000 would be trimmed resulting to 2:25:12.313) but should not be applied on the 2nd (as that would remove :01 resulting to 0:00).

Instead, we can just append a ".000" first and then trim the milliseconds part (which is after the dot .) to the first 3 characters [:3].

import datetime

def milliseconds_to_srt_time(t):
     """Converts the number of milliseconds to HH:MM:SS,ms time"""
     time_str = str(datetime.timedelta(milliseconds=t)) + ".000"
     time_str_split = time_str.split(".", maxsplit=1)
     return f"{time_str_split[0]},{time_str_split[1][:3]}"

print(milliseconds_to_srt_time(8712313))
print(milliseconds_to_srt_time(1000))
print(milliseconds_to_srt_time(1000000))
print(milliseconds_to_srt_time(4000400))
print(milliseconds_to_srt_time(80808231))
print(milliseconds_to_srt_time(80808000))

Output

2:25:12,313
0:00:01,000
0:16:40,000
1:06:40,400
22:26:48,231
22:26:48,000

score 0 · Answer 2 · answered Sep 21 '21 at 04:24

Here is another exemple of implementation, very similar though.

You can find other usefull information here : Format timedelta to string

import datetime

def milliseconds_to_str(t):
    """Converts the number of milliseconds to HH:MM:SS,ms time"""
    d = str(datetime.timedelta(milliseconds=t)).split(".")
    out = ":".join(["%02d" % (int(float(x))) for x in d[0].split(':')])
    return out + "," + ("%d" % (int(d[1])/1000) if len(d)==2 else "000")

print(milliseconds_to_str(8712313))
print(milliseconds_to_str(1000))
print(milliseconds_to_str(1000000))  
print(milliseconds_to_str(4000400)) 
print(milliseconds_to_str(80808231)) 
print(milliseconds_to_str(80808000))

The output is the same as Niel gave.

Why derive the output from the str repr of the timedelta object? Wouldn't it be more intuitive to derive directly from the timedelta object, e.g. its total_seconds attribute as shown in the question you linked? — FObersteiner, Sep 21 '21 at 05:49

Python datetime: convert milliseconds to string, preserving zeroes

2 Answers2