查看python源碼，發(fā)現(xiàn)里面的函數(shù)都以pass結(jié)尾，那么意義何在？

例如：

class str(object):
    """
    str(object='') -> str
    str(bytes_or_buffer[, encoding[, errors]]) -> str
    
    Create a new string object from the given object. If encoding or
    errors is specified, then the object must expose a data buffer
    that will be decoded using the given encoding and error handler.
    Otherwise, returns the result of object.__str__() (if defined)
    or repr(object).
    encoding defaults to sys.getdefaultencoding().
    errors defaults to 'strict'.
    """

其中一個函數(shù)
    def capitalize(self): # real signature unknown; restored from __doc__
        """
        S.capitalize() -> str
        
        Return a capitalized version of S, i.e. make the first character
        have upper case and the rest lower case.
        """
        return ""
        
這個函數(shù)到底返回了什么？難道返回了一個空字符嗎？

    def endswith(self, suffix, start=None, end=None): # real signature unknown; restored from __doc__
        """
        S.endswith(suffix[, start[, end]]) -> bool
        
        Return True if S ends with the specified suffix, False otherwise.
        With optional start, test S beginning at that position.
        With optional end, stop comparing S at that position.
        suffix can also be a tuple of strings to try.
        """
        return False

這個函數(shù)，返回False ，什么意思？
    def find(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
        """
        S.find(sub[, start[, end]]) -> int
        
        Return the lowest index in S where substring sub is found,
        such that sub is contained within S[start:end].  Optional
        arguments start and end are interpreted as in slice notation.
        
        Return -1 on failure.
        """
        return 0
這個返回一個0 ？

    def format(self, *args, **kwargs): # known special case of str.format
        """
        S.format(*args, **kwargs) -> str
        
        Return a formatted version of S, using substitutions from args and kwargs.
        The substitutions are identified by braces ('{' and '}').
        """
        pass

這個是一pass結(jié)尾的，那么要這個函數(shù)有什么意義

但是我在實際應(yīng)用他們的時候，返回的并不是這樣的？

我現(xiàn)在的以為是：這個類里面的這些函數(shù)，函數(shù)體里面什么邏輯都沒有寫？那么函數(shù)是怎么運行的？