How to define a function that recognizes my date format in python

I want to create a function or a loop with the conditional: if this string follows this format is a date, so return True, otherwise return False.

I already tried it with this code, but when I run is_date(string) it returns False, and it should return True.

string = '20090903'
def is_date(string):
    if string.format == "%YYYY%mm%dd":
        return True
    else:
        return False
is_date(string)

Try checking if the length is eight and the string only contains digits:

string = '20090903'
def is_date(string):
    return len(string) == 8 and string.isdigit()
print(is_date(string))

A more precise solution:

string = '20090903'
from dateutil.parser import parse 
def is_date(string):
    try:
        parse(string)
        return True
    except:
        return False
print(is_date(string))

This solution will give False on 00000000, but not the first solution:

Both Output:

True