How do I check if a file exists using Python?

You can also use

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

if you need to be sure it's a file.

You have the os.path.isfile function:

import os.path
os.path.isfile(file_path)

Unlike isfile(), exists() will yield True for directories.
So depending on if you want only plain files or also directories, you'll use isfile() or exists().

>>> print os.path.isfile("/etc/passwd")
True
>>> print os.path.isfile("/etc")
False
>>> print os.path.isfile("/does/not/exist")
False
>>> print os.path.exists("/etc/passwd")
True
>>> print os.path.exists("/etc")
True
>>> print os.path.exists("/does/not/exist")
False

Use os.path.isfile() with os.access():

import os
import os.path

PATH='./file.txt'

if os.path.isfile(PATH) and os.access(PATH, os.R_OK):
    print "File exists and is readable"
else:
    print "Either file is missing or is not readable"

import os
os.path.exists(filename)

Prefer the try statement. It's considered better style and avoids race conditions.

Don't take my word for it. There's plenty of support for this theory. Here's a couple:

• Style: Section "Handling unusual conditions" of http://allendowney.com/sd/notes/notes11.txt
• Avoiding Race Conditions

This is the simplest way to check if a file exists. Just because the file existed when you checked doesn't guarantee that it will be there when you need to open it.

import os
fname = "foo.txt"
if os.path.isfile(fname):
    print "file does exist at this time"
else:
    print "no such file"

import os

if os.path.isfile(filename):

It doesn't seem like there's a meaningful functional difference between try/except and exists(), so you should use which one makes sense.

If you want to read a file, if it exists, do

try:
    f = open(filepath)
except IOError:
    print 'Oh dear.'

But if you just wanted to rename a file if it exists, and therefore don't need to open it, do

if os.path.exists(filepath):
    os.rename(filepath, filepath + '.old')

If you want to write to a file, if it doesn't exist, do

if not os.path.exists(filepath):
    f = open(filepath, 'w')

If you need file locking, that's a different matter.

You could try this: (safer)

try:
    # http://effbot.org/zone/python-with-statement.htm
    # with is more safe to open file
    with open('whatever.txt') as fh: 
        # do something with fh
except IOError as e:
    print("({})".format(e))

the ouput would be:

([Errno 2] No such file or directory: 'whatever.txt')

then, depending on the result, your program can just keep running from there or you can code to stop it if you want.

Python 3.4 has an object-oriented path module: pathlib. Using this new module, you can check whether a file exists like this:

import pathlib
p = pathlib.Path('path/to/file')
if p.exists():
    # do stuff

You can (and usually should) still use a try/except block when opening files:

try:
    with p.open() as f:
        # do awesome stuff
except OSError:
    print('Well darn.')

The pathlib module has lots of cool stuff in it: convenient globbing, checking file's owner, easier path joining, etc. It's worth checking out.

Just to add to the confusion, it seems that the try: open() approach suggested above doesn't work in Python, as file access isn't exclusive, not even when writing to files, c.f. What is the best way to open a file for exclusive access in Python?.

Additionally, os.access().

You should definitely use this one.

from os.path import exists

if exists("file") == True:
    print "File exists."
elif exists("file") == False:
    print "File doesn't exist."

root,dirs,files = os.walk(LOCATION).next()
if myfile in files:
   print "yes it exists"

This is helpful when checking for several files. Or you want to do a set intersection/ subtraction with an existing list.

You can simply use tempfile module to know whether file exists or not:

import tempfile

tempfile._exists('filename') # return True or False

If you want to do what in bash would be

if [ -e '$FILE' ]; then
    prog '$FILE'
fi

which I sometimes do when using Python to do more complicated manipulation of a list of names (as I sometimes need to use Python for), the try open(file): except: method isn't really what's wanted, as it is not the Python process that is intended to open the file. In one case, the purpose is to filter a list of names according to whether they exist at present (and there are no processes likely to delete the file, nor security issues since this is on my Raspberry Pi which has no sensitive files on its SD).

I'm wondering whether a 'Simple Patterns' site would be a good idea? So that, for example, you could illustrate both methods with links between them and links to discussions as to when to use which pattern.

You can write Brian's suggestion without the try:.

from contextlib import suppress

with suppress(IOError), open('filename'): 
    process()

supress is part of Python 3.4. In older releases you can quickly write your own supress:

from contextlib import contextmanager

@contextmanager
def suppress(*exceptions):
    try:
        yield
    except exceptions:
        pass

You can use following open method to check if file exists + readable

open(inputFile, 'r')

This sample function will test for a file's presence in a very Pythonic way using try .. except:

def file_exists(filename):
    try:
        with open(filename) as f:
            return True
    except IOError:
        return False