Python日期时间模式匹配

Question

I'm trying to identify if a string can be cast as a date, according to a list of different formats. Thus, the whole list has to be looped over. If a match is found, that match should be returned. If all attempts return errors, that error should be returned. I'm not quite sure how to do this, my approach can be seen below.

_DEFAULT_PATTERNS = ["%d.%m.%Y", "%y-%m-%d"]
try:
    if format == 'default':
        for p in _DEFAULT_PATTERNS:
        try:
            value = datetime.strptime(value, p).date()
        except:
            continue
except Exception:
    return ERROR

return value

Answer 1

Your first choice would be to use dateutil.parser . If, however, the parser does not meet your needs, here's a version of your code, tidied up:

def parseDate(value):
    PATTERNS = ("%d.%m.%Y", "%y-%m-%d")
    for p in PATTERNS:
        try:
            return datetime.strptime(value, p).date()
        except ValueError:
            continue
    return False # No match found

Alternatively, raise an exception if the match is not found (instead of returning False ). This will make your function more similar to strptime :

    raise ValueError

Answer 2

Try something like this:

from datetime import datetime
_DEFAULT_PATTERNS = ["%d.%m.%Y", "%y-%m-%d"]
def is_castable_to_date(value):
    for p in _DEFAULT_PATTERNS:
        try:
            value = datetime.strptime(value, p).date()
            return True
        except:
            pass
    return False
print is_castable_to_date("12-12-12")
print is_castable_to_date("12.12.12")
print is_castable_to_date("12/12/12")