python strptime format with optional bits

问题:

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)?

回答1:

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')

回答2:

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')

回答3:

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.

回答4:

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.