variable "check" holds the function. and ambda describes the oneliner function.

mult = lambda a,b:a*b

is the same as

def mult(a,b):
return a*b

Try to use tools like debuggex:
https://www.debuggex.com/r/xN8wfXZE1Y4Qd3MO

It shows that your regexp matches two numbers and two any symbols, like this:

"11xx"

point "." match any symbol

may i see your regexp?

Done

fibonacci 1000th time... time to do something funny

it's classic oneliner.
def is ugly, lambda is beautiful in oneliner

zen of python, 1st line:
Beautiful is better than ugly.

No need to write python code.
Its regexp kata, you should edit this regexp string:

date_validator = r'\d\d\.\d\d.\d\d\d\d'

Read the wiki!

Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.

Great! That's why i made this kata - you reversed this algorithm better than me!

Great! Approved!

Added this line to the description:

Random tests can consist of numbers, ascii letters, some puctuation and brackets. But no need to check for line breaks (\n) and non-ASCII chatracters, nothing that fancy in the tests.

Multiline test cases are unnecessary, i think. The point of kata is to find a way to detect divisibility. It's not about fancy format checking...

Done

The point of this cata is regexp practice and understanding Gregorian calendar.