As you have already found out, the difference between exists and isfile is the fact that the former returns True in case the given path is a directory or a file, while the latter only returns True if the path points to a file.

Directories and files are quite similar from the technical point of view. A file can contain any kind of data. A directory is just a special entry in the file system (at least on Unix operating systems it is just a special file) that represents the fact that it may contain files and other directories. It is a helpful means for building up a data structure. Using directories, you can organize your data in a hierarchical structure.

Especially in the Windows world, directories are often called "folders". I am sure that you yourself are using "folders" for organizing your files.

A path is an unambiguous pointer to a resource in the file system. It can either point to a file or to a directory.

If the reason you're checking is so you can do something like if file_exists: open_it(), it's safer to use a try around the attempt to open it. Checking and then opening risks the file being deleted or moved or something between when you check and when you try to open it.

If you're not planning to open the file immediately, you can use os.path.isfile if you need to be sure it's a file.

Return True if path is an existing regular file. This follows symbolic links, so both islink() and isfile() can be true for the same path.

import os.path
os.path.isfile(fname)

pathlib

Starting with Python 3.4, the pathlib module offers an object-oriented approach (backported to pathlib2 in Python 2.7):

from pathlib import Path

my_file = Path("/path/to/file")
if my_file.is_file():
    # file exists

To check a directory, do:

if my_file.is_dir():
    # directory exists

To check whether a Path object exists independently of whether is it a file or directory, use exists():

if my_file.exists():
    # path exists

You can also use resolve(strict=True) in a try block:

try:
    my_abs_path = my_file.resolve(strict=True)
except FileNotFoundError:
    # doesn't exist
else:
    # exists