How do I check whether a file exists without exceptions?

Question

How do I check whether a file exists or not, without using the try statement?

Answer 1

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

Answer 2

Code:

import os
check_if_path_exists=lambda path:os.path.exists(path)

or:

import os
def check_if_path_exists(path):
    return os.path.exists(path)

This code checks whether the file or path specified by the argument path exists using the os.path.exists() function. It checks if the path exists and returns True if it exists and False if it doesn't exist. Example:

check_if_path_exists("C:/") #True
check_if_file_exists("ofhiafdajfihguihfa:/") #False 

Answer 3

Although almost every possible way has been listed in (at least one of) the existing answers (e.g. Python 3.4 specific stuff was added), I'll try to group everything together.

Note: every piece of Python standard library code that I'm going to post, belongs to version 3.5.3.

Problem statement:

1. Check file (arguable: also folder ("special" file) ?) existence

2. Don't use try / except / else / finally blocks

Possible solutions:

1. [Python.Docs]: os.path.exists(path)

Also check other function family members like os.path.isfile, os.path.isdir, os.path.lexists for slightly different behaviors:

Return True if path refers to an existing path or an open file descriptor. Returns False for broken symbolic links. On some platforms, this function may return False if permission is not granted to execute os.stat() on the requested file, even if the path physically exists.

All good, but if following the import tree:

• os.path - posixpath.py (ntpath.py)

  • genericpath.py - line ~20+

    def exists(path):
        """Test whether a path exists.  Returns False for broken symbolic links"""
        try:
            st = os.stat(path)
        except os.error:
            return False
        return True
    

it's just a try / except block around [Python.Docs]: os.stat(path, *, dir_fd=None, follow_symlinks=True). So, your code is try / except free, but lower in the framestack there's (at least) one such block. This also applies to other functions (including os.path.isfile).

1.1. [Python.Docs]: pathlib - Path.is_file()

• It's a fancier (and more [Wiktionary]: Pythonic) way of handling paths, but

• Under the hood, it does exactly the same thing (pathlib.py - line ~1330):

  def is_file(self):
      """
      Whether this path is a regular file (also True for symlinks pointing
          to regular files).
      """
      try:
          return S_ISREG(self.stat().st_mode)
      except OSError as e:
          if e.errno not in (ENOENT, ENOTDIR):
              raise
          # Path doesn't exist or is a broken symlink
          # (see https://bitbucket.org/pitrou/pathlib/issue/12/)
          return False
  

2. [Python.Docs]: With Statement Context Managers

Either:

• Create one:

  class Swallow:  # Dummy example
      swallowed_exceptions = (FileNotFoundError,)
  
      def __enter__(self):
          print("Entering...")
  
      def __exit__(self, exc_type, exc_value, exc_traceback):
          print("Exiting:", exc_type, exc_value, exc_traceback)
          # Only swallow FileNotFoundError (not e.g. TypeError - if the user passes a wrong argument like None or float or ...)
          return exc_type in Swallow.swallowed_exceptions
  

  • And its usage - I'll replicate the os.path.isfile behavior (note that this is just for demonstrating purposes, do not attempt to write such code for production):

    import os
    import stat
    
    
    def isfile_seaman(path):  # Dummy func
        result = False
        with Swallow():
            result = stat.S_ISREG(os.stat(path).st_mode)
        return result
    

• Use [Python.Docs]: contextlib.suppress(*exceptions) - which was specifically designed for selectively suppressing exceptions

But, they seem to be wrappers over try / except / else / finally blocks, as [Python.Docs]: Compound statements - The with statement states:

This allows common try...except...finally usage patterns to be encapsulated for convenient reuse.

3. Filesystem traversal functions

Search the results for matching item(s):

1. [Python.Docs]: os.listdir(path='.') (or [Python.Docs]: os.scandir(path='.') on Python v3.5+, backport: [PyPI]: scandir)

   • Under the hood, both use:

     • Nix: [Man7]: OPENDIR(3) / [Man7]: READDIR(3) / [Man7]: CLOSEDIR(3)

     • Win: [MS.Learn]: FindFirstFileW function (fileapi.h) / [MS.Learn]: FindNextFileW function (fileapi.h) / [MS.Learn]: FindClose function (fileapi.h)

     via [GitHub]: python/cpython - (main) cpython/Modules/posixmodule.c

   Using scandir() instead of listdir() can significantly increase the performance of code that also needs file type or file attribute information, because os.DirEntry objects expose this information if the operating system provides it when scanning a directory. All os.DirEntry methods may perform a system call, but is_dir() and is_file() usually only require a system call for symbolic links; os.DirEntry.stat() always requires a system call on Unix, but only requires one for symbolic links on Windows.

2. [Python.Docs]: os.walk(top, topdown=True, onerror=None, followlinks=False)

   • Uses os.listdir (os.scandir when available)

3. [Python.Docs]: glob.iglob(pathname, *, root_dir=None, dir_fd=None, recursive=False, include_hidden=False) (or its predecessor: glob.glob)

   • Doesn't seem a traversing function per se (at least in some cases), but it still uses os.listdir

Since these iterate over folders, (in most of the cases) they are inefficient for our problem (there are exceptions, like non wildcarded globbing - as @ShadowRanger pointed out), so I'm not going to insist on them. Not to mention that in some cases, filename processing might be required.

4. [Python.Docs]: os.access(path, mode, *, dir_fd=None, effective_ids=False, follow_symlinks=True)

Its behavior is close to os.path.exists (actually it's wider, mainly because of the 2^nd argument).

• User permissions might restrict the file "visibility" as the doc states:

  ... test if the invoking user has the specified access to path. mode should be F_OK to test the existence of path...

• Security considerations:

  Using access() to check if a user is authorized to e.g. open a file before actually doing so using open() creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it.

os.access("/tmp", os.F_OK)

Since I also work in C, I use this method as well because under the hood, it calls native APIs (again, via "${PYTHON_SRC_DIR}/Modules/posixmodule.c"), but it also opens a gate for possible user errors, and it's not as Pythonic as other variants. So, don't use it unless you know what you're doing:

• Nix: [Man7]: ACCESS(2)

  Warning: Using these calls to check if a user is authorized to, for example, open a file before actually doing so using open(2) creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it. For this reason, the use of this system call should be avoided.

• Win: [MS.Learn]: GetFileAttributesW function (fileapi.h)

As seen, this approach is highly discouraged (especially on Nix).

Note: calling native APIs is also possible via [Python.Docs]: ctypes - A foreign function library for Python, but in most cases it's more complicated. Before working with CTypes, check [SO]: C function called from Python via ctypes returns incorrect value (@CristiFati's answer) out.

(Win specific): since vcruntime###.dll (msvcr###.dll for older VStudio versions - I'm going to refer to it as UCRT) exports a [MS.Learn]: _access, _waccess function family as well, here's an example (note that the recommended [Python.Docs]: msvcrt - Useful routines from the MS VC++ runtime doesn't export them):

Python 3.5.3 (v3.5.3:1880cb95a742, Jan 16 2017, 16:02:32) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import ctypes as cts, os
>>> cts.CDLL("msvcrt")._waccess(u"C:\\Windows\\Temp", os.F_OK)
0
>>> cts.CDLL("msvcrt")._waccess(u"C:\\Windows\\Temp.notexist", os.F_OK)
-1

Notes:

• Although it's not a good practice, I'm using os.F_OK in the call, but that's just for clarity (its value is 0)

• I'm using _waccess so that the same code works on Python 3 and Python 2 (in spite of [Wikipedia]: Unicode related differences between them - [SO]: Passing utf-16 string to a Windows function (@CristiFati's answer))

• Although this targets a very specific area, it was not mentioned in any of the previous answers

The Linux (Ubuntu ([Wikipedia]: Ubuntu version history) 16 x86_64 (pc064)) counterpart as well:

Python 3.5.2 (default, Nov 17 2016, 17:05:23)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ctypes as cts, os
>>> cts.CDLL("/lib/x86_64-linux-gnu/libc.so.6").access(b"/tmp", os.F_OK)
0
>>> cts.CDLL("/lib/x86_64-linux-gnu/libc.so.6").access(b"/tmp.notexist", os.F_OK)
-1

Notes:

• Instead hardcoding libc.so (LibC)'s path ("/lib/x86_64-linux-gnu/libc.so.6") which may (and most likely, will) vary across systems, None (or the empty string) can be passed to CDLL constructor (ctypes.CDLL(None).access(b"/tmp", os.F_OK)). According to [Man7]: DLOPEN(3):

  If filename is NULL, then the returned handle is for the main program. When given to dlsym(3), this handle causes a search for a symbol in the main program, followed by all shared objects loaded at program startup, and then all shared objects loaded by dlopen() with the flag RTLD_GLOBAL.

• Main (current) program (python) is linked against LibC, so its symbols (including access) will be loaded

• This has to be handled with care, since functions like main, Py_Main and (all the) others are available; calling them could have disastrous effects (on the current program)

• This doesn't also apply to Windows (but that's not such a big deal, since UCRT is located in "%SystemRoot%\System32" which is in %PATH% by default). I wanted to take things further and replicate this behavior on Windows (and submit a patch), but as it turns out, [MS.Learn]: GetProcAddress function (libloaderapi.h) only "sees" exported symbols, so unless someone declares the functions in the main executable as __declspec(dllexport) (why on Earth the common person would do that?), the main program is loadable, but it is pretty much unusable

5. 3^rd-party modules with filesystem capabilities

Most likely, will rely on one of the ways above (maybe with slight customizations).
One example would be (again, Win specific) [GitHub]: mhammond/pywin32 - Python for Windows (pywin32) Extensions, which is a Python wrapper over WinAPIs.

But, since this is more like a workaround, I'm stopping here.

6. SysAdmin approach

I consider this a (lame) workaround (gainarie): use Python as a wrapper to execute shell commands:

• Win:

  (py35x64_test) [cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q000082831]> "e:\Work\Dev\VEnvs\py35x64_test\Scripts\python.exe" -c "import os; print(os.system('dir /b \"C:\\Windows\\Temp\" > nul 2>&1'))"
  0
  
  (py35x64_test) [cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q000082831]> "e:\Work\Dev\VEnvs\py35x64_test\Scripts\python.exe" -c "import os; print(os.system('dir /b \"C:\\Windows\\Temp.notexist\" > nul 2>&1'))"
  1
  

• Nix ([Wikipedia]: Unix-like) - Ubuntu:

  [cfati@cfati-5510-0:/mnt/e/Work/Dev/StackOverflow/q000082831]> python3 -c "import os; print(os.system('ls \"/tmp\" > /dev/null 2>&1'))"
  0
  [cfati@cfati-5510-0:/mnt/e/Work/Dev/StackOverflow/q000082831]> python3 -c "import os; print(os.system('ls \"/tmp.notexist\" > /dev/null 2>&1'))"
  512
  

Bottom line:

• Do use try / except / else / finally blocks, because they can prevent you running into a series of nasty problems

• A possible counterexample that I can think of, is performance: such blocks are costly, so try not to place them in code that it's supposed to run hundreds of thousands times per second (but since (in most cases) it involves disk access, it won't be the case)

Answer 4

Here's a one-line Python command for the Linux command line environment. I find this very handy since I'm not such a hot Bash guy.

python -c "import os.path; print os.path.isfile('/path_to/file.xxx')"

Answer 5

Use:

import os
#Your path here e.g. "C:\Program Files\text.txt"
#For access purposes: "C:\\Program Files\\text.txt"
if os.path.exists("C:\..."):
    print "File found!"
else:
    print "File not found!"

Importing os makes it easier to navigate and perform standard actions with your operating system.

For reference, also see How do I check whether a file exists without exceptions?.

If you need high-level operations, use shutil.

Answer 6

if os.path.isfile(path_to_file):
    try:
        open(path_to_file)
            pass
    except IOError as e:
        print "Unable to open file"

Raising exceptions is considered to be an acceptable, and Pythonic, approach for flow control in your program. Consider handling missing files with IOErrors. In this situation, an IOError exception will be raised if the file exists but the user does not have read permissions.

Source: Using Python: How To Check If A File Exists

Answer 7

If the file is for opening you could use one of the following techniques:

with open('somefile', 'xt') as f: # Using the x-flag, Python 3.3 and above
    f.write('Hello\n')

if not os.path.exists('somefile'): 
    with open('somefile', 'wt') as f:
        f.write("Hello\n")
else:
    print('File already exists!')

---

Note: This finds either a file or a directory with the given name.

Answer 8

It doesn't seem like there's a meaningful functional difference between try/except and isfile(), 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.isfile(filepath):
    os.rename(filepath, filepath + '.old')

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

# Python 2
if not os.path.isfile(filepath):
    f = open(filepath, 'w')

# Python 3: x opens for exclusive creation, failing if the file already exists
try:
    f = open(filepath, 'wx')
except IOError:
    print 'file already exists'

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

Answer 9

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 these course notes for Software Design (2007)
• Avoiding Race Conditions

Answer 10

Unlike isfile(), exists() will return True for directories. So depending on if you want only plain files or also directories, you'll use isfile() or exists(). Here is some simple REPL output:

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

Answer 11

Use os.path.exists to check both files and directories:

import os.path
os.path.exists(file_path)

Use os.path.isfile to check only files (note: follows symbolic links):

os.path.isfile(file_path)

Answer 12

Use:

import os

# For testing purposes the arguments defaulted to the current folder and file.
# returns True if file found
def file_exists(FOLDER_PATH='../', FILE_NAME=__file__):
    return os.path.isdir(FOLDER_PATH) \
        and os.path.isfile(os.path.join(FOLDER_PATH, FILE_NAME))

It is basically a folder check, and then a file check with the proper directory separator using os.path.join.

Answer 13

Check file or directory exists

You can follow these three ways:

1. Using isfile()

Note 1: The os.path.isfile used only for files

import os.path
os.path.isfile(filename) # True if file exists
os.path.isfile(dirname) # False if directory exists

2. Using exists

Note 2: The os.path.exists is used for both files and directories

import os.path
os.path.exists(filename) # True if file exists
os.path.exists(dirname) # True if directory exists

3. The pathlib.Path method (included in Python 3+, installable with pip for Python 2)

from pathlib import Path
Path(filename).exists()

Answer 14

Date: 2017-12-04

Every possible solution has been listed in other answers.

An intuitive and arguable way to check if a file exists is the following:

import os

os.path.isfile('~/file.md')  # Returns True if exists, else False

# Additionally, check a directory
os.path.isdir('~/folder')  # Returns True if the folder exists, else False

# Check either a directory or a file
os.path.exists('~/file')

I made an exhaustive cheat sheet for your reference:

# os.path methods in exhaustive cheat sheet
{'definition': ['dirname',
               'basename',
               'abspath',
               'relpath',
               'commonpath',
               'normpath',
               'realpath'],
'operation': ['split', 'splitdrive', 'splitext',
               'join', 'normcase'],
'compare': ['samefile', 'sameopenfile', 'samestat'],
'condition': ['isdir',
              'isfile',
              'exists',
              'lexists'
              'islink',
              'isabs',
              'ismount',],
 'expand': ['expanduser',
            'expandvars'],
 'stat': ['getatime', 'getctime', 'getmtime',
          'getsize']}

Answer 15

TL;DR
The answer is: use the pathlib module

---

Pathlib is probably the most modern and convenient way for almost all of the file operations. For the existence of a file or a folder a single line of code is enough. If file is not exists, it will not throw any exception.

from pathlib import Path

if Path("myfile.txt").exists(): # works for both file and folders
    # do your cool stuff...

The pathlib module was introduced in Python 3.4, so you need to have Python 3.4+. This library makes your life much easier while working with files and folders, and it is pretty to use. Here is more documentation about it: pathlib — Object-oriented filesystem paths.

BTW, if you are going to reuse the path, then it is better to assign it to a variable.

So it will become:

from pathlib import Path

p = Path("loc/of/myfile.txt")
if p.exists(): # works for both file and folders
    # do stuffs...
#reuse 'p' if needed.

Answer 16

Another possible option is to check whether the filename is in the directory using os.listdir():

import os
if 'foo.txt' in os.listdir():
    # Do things

This will return true if it is and false if not.

Answer 17

This is how I found a list of files (in these images) in one folder and searched it in a folder (with subfolders):

# This script concatenates JavaScript files into a unified JavaScript file to reduce server round-trips

import os
import string
import math
import ntpath
import sys

#import pyodbc

import gzip
import shutil

import hashlib

# BUF_SIZE is totally arbitrary, change for your app!
BUF_SIZE = 65536  # Let’s read stuff in 64 kilobyte chunks

# Iterate over all JavaScript files in the folder and combine them
filenames = []
shortfilenames = []

imgfilenames = []
imgshortfilenames = []

# Get a unified path so we can stop dancing with user paths.
# Determine where files are on this machine (%TEMP% directory and application installation directory)
if '.exe' in sys.argv[0]: # if getattr(sys, 'frozen', False):
    RootPath = os.path.abspath(os.path.join(__file__, "..\\"))

elif __file__:
    RootPath = os.path.abspath(os.path.join(__file__, "..\\"))

print ("\n storage of image files RootPath: %s\n" %RootPath)

FolderPath = "D:\\TFS-FARM1\\StoneSoup_STS\\SDLC\\Build\\Code\\StoneSoup_Refactor\\StoneSoupUI\\Images"
print ("\n storage of image files in folder to search: %s\n" %FolderPath)

for root, directories, filenames2 in os.walk(FolderPath):
    for filename in filenames2:
        fullname = os.path.join(root, filename)
        filenames.append(fullname)
        shortfilenames.append(filename)

for i, fname in enumerate(shortfilenames):
        print("%s - %s" % (i+1, fname))

for root, directories, filenames2 in os.walk(RootPath):
    for filename in filenames2:
        fullname = os.path.join(root, filename)
        imgfilenames.append(fullname)
        imgshortfilenames.append(filename)

for i, fname in enumerate(imgshortfilenames):
        print("%s - %s" % (i+1, fname))

for i, fname in enumerate(imgshortfilenames):
        if fname in shortfilenames:
            print("%s - %s exists" % (i+1, fname))
        else:
            print("%s - %s ABSENT" % (i+1, fname))

Answer 18

import os

if os.path.isfile(filepath):
   print("File exists")

Answer 19

Use os.path.exists() to check whether file exists or not:

def fileAtLocation(filename,path):
    return os.path.exists(path + filename)
 

filename="dummy.txt"
path = "/home/ie/SachinSaga/scripts/subscription_unit_reader_file/"


if fileAtLocation(filename,path):
   print('file found at location..')
else:
   print('file not found at location..')

Answer 20

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.is_file():  # or p.is_dir() to see if it is a directory
    # 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. If you're on an older Python (version 2.6 or later), you can still install pathlib with pip:

# installs pathlib2 on older Python versions
# the original third-party module, pathlib, is no longer maintained.
pip install pathlib2

Then import it as follows:

# Older Python versions
import pathlib2 as pathlib

Answer 21

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

import os

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

Answer 22

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

file = open(inputFile, 'r')
file.close()

Answer 23

exists() and is_file() methods of 'Path' object can be used for checking if a given path exists and is a file.

Python 3 program to check if a file exists:

# File name:  check-if-file-exists.py

from pathlib import Path

filePath = Path(input("Enter path of the file to be found: "))

if filePath.exists() and filePath.is_file():
    print("Success: File exists")
else:
    print("Error: File does not exist")

Output:

$ python3 check-if-file-exists.py

Enter path of the file to be found: /Users/macuser1/stack-overflow/index.html

Success: File exists

$ python3 check-if-file-exists.py

Enter path of the file to be found: hghjg jghj

Error: File does not exist

Answer 24

If you imported NumPy already for other purposes then there is no need to import other libraries like pathlib, os, paths, etc.

import numpy as np
np.DataSource().exists("path/to/your/file")

This will return true or false based on its existence.

Answer 25

import os
os.path.exists(path) # Returns whether the path (directory or file) exists or not
os.path.isfile(path) # Returns whether the file exists or not

Answer 26

How do I check whether a file exists, using Python, without using a try statement?

Now available since Python 3.4, import and instantiate a Path object with the file name, and check the is_file method (note that this returns True for symlinks pointing to regular files as well):

>>> from pathlib import Path
>>> Path('/').is_file()
False
>>> Path('/initrd.img').is_file()
True
>>> Path('/doesnotexist').is_file()
False

If you're on Python 2, you can backport the pathlib module from pypi, pathlib2, or otherwise check isfile from the os.path module:

>>> import os
>>> os.path.isfile('/')
False
>>> os.path.isfile('/initrd.img')
True
>>> os.path.isfile('/doesnotexist')
False

Now the above is probably the best pragmatic direct answer here, but there's the possibility of a race condition (depending on what you're trying to accomplish), and the fact that the underlying implementation uses a try, but Python uses try everywhere in its implementation.

Because Python uses try everywhere, there's really no reason to avoid an implementation that uses it.

But the rest of this answer attempts to consider these caveats.

Longer, much more pedantic answer

Available since Python 3.4, use the new Path object in pathlib. Note that .exists is not quite right, because directories are not files (except in the unix sense that everything is a file).

>>> from pathlib import Path
>>> root = Path('/')
>>> root.exists()
True

So we need to use is_file:

>>> root.is_file()
False

Here's the help on is_file:

is_file(self)
    Whether this path is a regular file (also True for symlinks pointing
    to regular files).

So let's get a file that we know is a file:

>>> import tempfile
>>> file = tempfile.NamedTemporaryFile()
>>> filepathobj = Path(file.name)
>>> filepathobj.is_file()
True
>>> filepathobj.exists()
True

By default, NamedTemporaryFile deletes the file when closed (and will automatically close when no more references exist to it).

>>> del file
>>> filepathobj.exists()
False
>>> filepathobj.is_file()
False

If you dig into the implementation, though, you'll see that is_file uses try:

def is_file(self):
    """
    Whether this path is a regular file (also True for symlinks pointing
    to regular files).
    """
    try:
        return S_ISREG(self.stat().st_mode)
    except OSError as e:
        if e.errno not in (ENOENT, ENOTDIR):
            raise
        # Path doesn't exist or is a broken symlink
        # (see https://bitbucket.org/pitrou/pathlib/issue/12/)
        return False

Race Conditions: Why we like try

We like try because it avoids race conditions. With try, you simply attempt to read your file, expecting it to be there, and if not, you catch the exception and perform whatever fallback behavior makes sense.

If you want to check that a file exists before you attempt to read it, and you might be deleting it and then you might be using multiple threads or processes, or another program knows about that file and could delete it - you risk the chance of a race condition if you check it exists, because you are then racing to open it before its condition (its existence) changes.

Race conditions are very hard to debug because there's a very small window in which they can cause your program to fail.

But if this is your motivation, you can get the value of a try statement by using the suppress context manager.

Avoiding race conditions without a try statement: suppress

Python 3.4 gives us the suppress context manager (previously the ignore context manager), which does semantically exactly the same thing in fewer lines, while also (at least superficially) meeting the original ask to avoid a try statement:

from contextlib import suppress
from pathlib import Path

Usage:

>>> with suppress(OSError), Path('doesnotexist').open() as f:
...     for line in f:
...         print(line)
... 
>>>
>>> with suppress(OSError):
...     Path('doesnotexist').unlink()
... 
>>> 

For earlier Pythons, you could roll your own suppress, but without a try will be more verbose than with. I do believe this actually is the only answer that doesn't use try at any level in the Python that can be applied to prior to Python 3.4 because it uses a context manager instead:

class suppress(object):
    def __init__(self, *exceptions):
        self.exceptions = exceptions
    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_value, traceback):
        if exc_type is not None:
            return issubclass(exc_type, self.exceptions)

Perhaps easier with a try:

from contextlib import contextmanager

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

Other options that don't meet the ask for "without try":

isfile

import os
os.path.isfile(path)

from the docs:

os.path.isfile(path)

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.

But if you examine the source of this function, you'll see it actually does use a try statement:

# This follows symbolic links, so both islink() and isdir() can be true
# for the same path on systems that support symlinks
def isfile(path):
    """Test whether a path is a regular file"""
    try:
        st = os.stat(path)
    except os.error:
        return False
    return stat.S_ISREG(st.st_mode)

>>> OSError is os.error
True

All it's doing is using the given path to see if it can get stats on it, catching OSError and then checking if it's a file if it didn't raise the exception.

If you intend to do something with the file, I would suggest directly attempting it with a try-except to avoid a race condition:

try:
    with open(path) as f:
        f.read()
except OSError:
    pass

os.access

Available for Unix and Windows is os.access, but to use you must pass flags, and it does not differentiate between files and directories. This is more used to test if the real invoking user has access in an elevated privilege environment:

import os
os.access(path, os.F_OK)

It also suffers from the same race condition problems as isfile. From the docs:

Note: Using access() to check if a user is authorized to e.g. open a file before actually doing so using open() creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it. It’s preferable to use EAFP techniques. For example:

if os.access("myfile", os.R_OK):
    with open("myfile") as fp:
        return fp.read()
return "some default data"

is better written as:

try:
    fp = open("myfile")
except IOError as e:
    if e.errno == errno.EACCES:
        return "some default data"
    # Not a permission error.
    raise
else:
    with fp:
        return fp.read()

Avoid using os.access. It is a low level function that has more opportunities for user error than the higher level objects and functions discussed above.

Criticism of another answer:

Another answer says this about os.access:

Personally, I prefer this one because under the hood, it calls native APIs (via "${PYTHON_SRC_DIR}/Modules/posixmodule.c"), but it also opens a gate for possible user errors, and it's not as Pythonic as other variants:

This answer says it prefers a non-Pythonic, error-prone method, with no justification. It seems to encourage users to use low-level APIs without understanding them.

It also creates a context manager which, by unconditionally returning True, allows all Exceptions (including KeyboardInterrupt and SystemExit!) to pass silently, which is a good way to hide bugs.

This seems to encourage users to adopt poor practices.

Answer 27

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 exists at this time")

Answer 28

In 2016 the best way is still using os.path.isfile:

>>> os.path.isfile('/path/to/some/file.txt')

Or in Python 3 you can use pathlib:

import pathlib
path = pathlib.Path('/path/to/some/file.txt')
if path.is_file():
    ...

Answer 29

I'm the author of a package that's been around for about 10 years, and it has a function that addresses this question directly. Basically, if you are on a non-Windows system, it uses Popen to access find. However, if you are on Windows, it replicates find with an efficient filesystem walker.

The code itself does not use a try block… except in determining the operating system and thus steering you to the "Unix"-style find or the hand-buillt find. Timing tests showed that the try was faster in determining the OS, so I did use one there (but nowhere else).

>>> import pox
>>> pox.find('*python*', type='file', root=pox.homedir(), recurse=False)
['/Users/mmckerns/.python']

And the doc…

>>> print pox.find.__doc__
find(patterns[,root,recurse,type]); Get path to a file or directory

    patterns: name or partial name string of items to search for
    root: path string of top-level directory to search
    recurse: if True, recurse down from root directory
    type: item filter; one of {None, file, dir, link, socket, block, char}
    verbose: if True, be a little verbose about the search

    On some OS, recursion can be specified by recursion depth (an integer).
    patterns can be specified with basic pattern matching. Additionally,
    multiple patterns can be specified by splitting patterns with a ';'
    For example:
        >>> find('pox*', root='..')
        ['/Users/foo/pox/pox', '/Users/foo/pox/scripts/pox_launcher.py']

        >>> find('*shutils*;*init*')
        ['/Users/foo/pox/pox/shutils.py', '/Users/foo/pox/pox/__init__.py']

>>>

The implementation, if you care to look, is here: https://github.com/uqfoundation/pox/blob/89f90fb308f285ca7a62eabe2c38acb87e89dad9/pox/shutils.py#L190

Answer 30

How do I check whether a file exists, without using the try statement?

In 2016, this is still arguably the easiest way to check if both a file exists and if it is a file:

import os
os.path.isfile('./file.txt')    # Returns True if exists, else False

isfile is actually just a helper method that internally uses os.stat and stat.S_ISREG(mode) underneath. This os.stat is a lower-level method that will provide you with detailed information about files, directories, sockets, buffers, and more. More about os.stat here

Note: However, this approach will not lock the file in any way and therefore your code can become vulnerable to "time of check to time of use" (TOCTTOU) bugs.

So raising exceptions is considered to be an acceptable, and Pythonic, approach for flow control in your program. And one should consider handling missing files with IOErrors, rather than if statements (just an advice).