Base class for file-like objects? (a.k.a "Stream" in Java)

[Gabriel Genellina]

En Tue, 24 Jul 2007 19:51:30 -0300, Boris Dušek <boris.dusek at gmail.com>  
escribió:

> in Java, when I want to pass input to a function, I pass
> "InputStream", which is a base class of any input stream.
>
> In Python, I found that "file" objects exist. While specifying
> argument types in Python is not possible as in Java, it is possible to
> check whether an object is an instance of some class and that's what I
> need - I need to check if an argument is a "file"-like object, and if
> yes, behave accordingly, if not, treat the argument as string with
> URL.

No, it's not what you need, it's what you *think* you need :)

> P.S.: The code should finally look in esence something like this:

Posting this is much better that saying what you think you need.

> if isinstance(f, file):
>    pass
> elif isinstance(f, string):
>    f = urllib.urlopen(f)
> else:
>    raise "..."
> process_stream(f)

I can imagine that process_stream is something like this:

def process_stream(f):
   ...
   data = f.read()
   ...

or similar. Then, you dont need a file object: you need something with a  
read() method. So, this is what you should check in your code above.

if hasattr(f, "read"):
   pass
elif isinstance(f, basestring):
   f = urllib.urlopen(f)
else:
   raise TypeError, "Expecting either a readable file-like object or an URL"
process_stream(f)

Or perhaps:

if isinstance(f, basestring):
   f = urllib.urlopen(f)
process_stream(f)

and just let the exception happen below at f.read - which explains itself  
rather well.

-- 
Gabriel Genellina