Pfthb

I have a @asynccontextmanager method named opened() that is an instance method of a class File. Sometimes I call it using a class by mistake like so File.opened(). It then fails because the object is not initialized (e.g. name) with an error that does not really express the problem.

AttributeError: 'str' object has no attribute 'opened'

Is there a way to prevent this?

Example

class File: 
 def __init__(self, file_name):
 self.file_name = file_name

 @asynccontextmanager
 async def opened(self):
 open(self.file_name)
 # do other things

This should be OK:

file = File('input.csv')
async with file.opened() as file_handle:
 #do stuff

But his should yield an error telling me that I can't use a instance method without creating an object first:

async with File.opened() as file_handle:
 # does not work, and should not be allowed

You can check if self is an instance of File so that you can raise an exception with a friendlier error message:

@asynccontextmanager
async def opened(self):
 if not isinstance(self, File):
 raise RuntimeError('opened() must be called as a method bound to a File instance.')
 open(self.file_name)