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'.

"""

其中一个函数

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 ""

这个函数到底返回了什么？难道返回了一个空字符吗？

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

这个函数，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

这个返回一个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

这个是一pass结尾的，那么要这个函数有什么意义

但是我在实际应用他们的时候，返回的并不是这样的？

我现在的以为是：这个类里面的这些函数，函数体里面什么逻辑都没有写？那么函数是怎么运行的？