How is this possible? What is the explaination

Part d: float check string has a method s. isdigit() that returns true if string s contains only digits and false otherwise, i. e. s is a string that represents an integer. write a function named float_check that takes one parameter that is a string and returns true if the string represents a float and false otherwise. for the purpose of this function we define a float to be a string of digits that has at most one decimal point. note that under this definition an integer argument will return true. remember “edge cases” such as “45.” or “.45”; both should return true. for example: float_check('1234') returns true float_check('123.45') returns true float_check('123.45.67') returns false float_check('34e46') returns false float_check('.45') returns true float_check('45.') returns true float_check('45..') returns false