python strptime format with optional bits

Right now I have:

timestamp = datetime.strptime(date_string, '%Y-%m-%d %H:%M:%S.%f')

This works great unless I'm converting a string that doesn't have the microseconds. How can I specify that the microseconds are optional (and should be considered 0 if they aren't in the string)?

You could use a try/except block:

try:
    timestamp = datetime.strptime(date_string, '%Y-%m-%d %H:%M:%S.%f')
except ValueError:
    timestamp = datetime.strptime(date_string, '%Y-%m-%d %H:%M:%S')

What about just appending it if it doesn't exist?

if '.' not in date_string:
    date_string = date_string + '.0'

timestamp = datetime.strptime(date_string, '%Y-%m-%d %H:%M:%S.%f')

I'm late to the party but I found if you don't care about the optional bits this will lop off the .%f for you.

datestring.split('.')[0]

I prefer using regex matches instead of try and except. This allows for many fallbacks of acceptable formats.

# full timestamp with milliseconds
match = re.match(r"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d+Z", date_string)
if match:
    return datetime.strptime(date_string, "%Y-%m-%dT%H:%M:%S.%fZ")

# timestamp missing milliseconds
match = re.match(r"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z", date_string)
if match:
    return datetime.strptime(date_string, "%Y-%m-%dT%H:%M:%SZ")

# timestamp missing milliseconds & seconds
match = re.match(r"\d{4}-\d{2}-\d{2}T\d{2}:\d{2}Z", date_string)
if match:
    return datetime.strptime(date_string, "%Y-%m-%dT%H:%MZ")

# unknown timestamp format
return false

Don't forget to import "re" as well as "datetime" for this method.

datetime(*map(int, re.findall('\d+', date_string)))

can parse both '%Y-%m-%d %H:%M:%S.%f' and '%Y-%m-%d %H:%M:%S'. It is too permissive if your input is not filtered.

It is quick-and-dirty but sometimes strptime() is too slow. It can be used if you know that the input has the expected date format.

using one regular expression and some list expressions

time_str = "12:34.567"
# time format is [HH:]MM:SS[.FFF]
sum([a*b for a,b in zip(map(lambda x: int(x) if x else 0, re.match(r"(?:(\d{2}):)?(\d{2}):(\d{2})(?:\.(\d{3}))?", time_str).groups()), [3600, 60, 1, 1/1000])])
# result = 754.567

If you are using Pandas you can also filter the the Series and concatenate it. The index is automatically joined.

import pandas as pd

# Every other row has a different format
df = pd.DataFrame({"datetime_string": ["21-06-08 14:36:09", "21-06-08 14:36:09.50", "21-06-08 14:36:10", "21-06-08 14:36:10.50"]})
df["datetime"] = pd.concat([
    pd.to_datetime(df["datetime_string"].iloc[1::2], format="%y-%m-%d %H:%M:%S.%f"),
    pd.to_datetime(df["datetime_string"].iloc[::2], format="%y-%m-%d %H:%M:%S"),
])

	datetime_string	datetime
0	21-06-08 14:36:09	2021-06-08 14:36:09
1	21-06-08 14:36:09.50	2021-06-08 14:36:09.500000
2	21-06-08 14:36:10	2021-06-08 14:36:10
3	21-06-08 14:36:10.50	2021-06-08 14:36:10.500000

For my similar problem using jq I used the following:

|split("Z")[0]|split(".")[0]|strptime("%Y-%m-%dT%H:%M:%S")|mktime

As the solution to sort my list by time properly.