Python Forum

you can detect if x is a float like:

if isinstance(x,float):
    ...

so how do you detect if x is a file?

isinstance(x, file)

file is no longer a built-in functions for Python 3.x.
This work Python 2.7 and 3.6.

>>> from io import IOBase

>>> f = open('hello.txt')
>>> isinstance(f, IOBase)
True

But remember type checking is really not good at all in Pythons,so use it sparse.

Quote:EAFP(Easier to ask for forgiveness than permission).

So let error occur then can catch it with try except.

LBYL(Look before you leap) check type before error occur,like in language like C/C++.

if you have the path you can check with os.path.isfile

i want to check if what is passed to a function in stdout= is a file or file descriptor. for file descriptor, checking for int is good enough. but assuming whatever is not int is a file i think is not good enough ... something might succeed with something else. i want an explicit test. right now i am checking if 'fileno' in stdout. i want this to work in the widest range of python versions as possible but at least 2.6-2.7 and 3.3-.

(Feb-11-2017, 02:42 AM)Skaperen Wrote: [ -> ]but assuming whatever is not int is a file i think is not good enough ... something might succeed with something else.

Why is that not good enough? If it quacks like a duck, treat it like a duck. If it doesn't quack, then just raise an exception.

I also don't understand what you mean about file descriptors. That sounds like C-talk. In Python, it's an object, not a numeric.

(Feb-11-2017, 03:54 AM)micseydel Wrote: [ -> ]I also don't understand what you mean about file descriptors. That sounds like C-talk. In Python, it's an object, not a numeric.

as in os.pipe() ... how i connect 2 or more processes together in a command pipeline.

Just ask nicely if it's a file?

>>> import os
>>> os.path.isfile("test.db")
True
>>> os.path.isfile("pipe://4433828") #...or whatever
False

File vs file descriptor is needed in C, when you have to deal with file handles.
I have never cared in python, and it hasn't hurt me yet.
If you want strict type checking then you should go back to programming in C.

In [1]: import os.path

In [2]: with open('39768.txt', 'r') as f:
   ...:     print(os.path.isfile(f.fileno()))
   ...:     
True

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