I am making my first attempt to use type hinting in a new project, and
I'm quickly hitting areas that I'm having trouble understanding. One of
them is how to write type hints for a method decorator.
Here is an example that illustrates my confusion. (Sorry for the
length.)
import collections.abc
class BufferScanner(object):
def __init__(self, buf: str) -> None:
self._buffer = buf
self._index = 0
self._eof = False
self._line = 1
self._column = 1
@property
def eof(self) -> bool:
return self._eof
@staticmethod
def _check_eof(method: collections.abc.Callable -> (
collections.abc.Callable
):
def wrapper(*args, **kwargs):
self = args[0]
if not self._eof:
method(*args, **kwargs)
if self._index >= len(self._buffer):
self._eof = True
return self._eof
return wrapper
@_check_eof
def next_line(self) -> None:
"""Advance the scanner to the beginning of the next line."""
try:
i = self._buffer.index('\n', self._index)
except ValueError:
self._index = len(self._buffer) # decorator will set _eof
return
self._index = i + 1 # move past the newline
self._line += 1
self._column = 1
I cannot figure out how to correctly specify the Callable argument and
return type for _check_eof(). As indicated by the name, method should
be a method (of the BufferScanner class), so its first positional
argument should always be an instance of BufferScanner, but it could
have any combination of positional and/or keyword arguments after that.
I've read the TypeVar and ParamSpec documentation, and me head is
spinning, but neither one really seems to help with this situation.
Any pointers to good resources or the correct way to do this are
appreciated.
Thanks!
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