How to determine whether a file exists using Python

Usually before reading and writing files, you need to determine whether the file or directory exists, otherwise some processing methods may cause program errors. So it is best to determine whether the file exists before doing any operation.

Here will introduce three methods to determine whether a file or folder exists, using the os module, Try statement, and pathlib module respectively.

1. Use the os module

The os.path.exists() method in the os module is used to check whether the file exists.

Judge whether the file exists

import os
os.path.exists(test_file.txt)
#True
os.path.exists(no_exist_file.txt)
#False

Judge whether the folder exists

import os
os.path.exists(test_dir)
#True
os.path.exists(no_exist_dir)
#False

It can be seen that the os.path.exists() method is used to judge whether the file and the folder are the same.

In fact, there is still a problem with this method. Suppose you want to check whether the file "test_data" exists, but there is a folder called "test_data" under the current path, so a misjudgment may occur. In order to avoid this situation, you can do this:

Only check the file

import os
os.path.isfile("test-data")

With this method, False will be returned if the file "test-data" does not exist, and True will be returned otherwise.

Even if the file exists, you may also need to determine whether the file can be read and written.

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Determine whether the file can be read and written

Use the os.access() method to determine whether the file can be read and written.

Syntax:

os.access(path, mode)

path is the file path, mode is the operating mode, there are several types:

os.F_OK: Check whether the file exists;

os.R_OK: Check whether the file is readable;

os.W_OK: Check whether the file can be written;

os.X_OK: Check whether the file can be executed

The method returns True or False by determining whether the file path exists and the permissions of various access modes.

import os
if os.access("/file/path/foo.txt", os.F_OK):
    print "Given file path is exist."
if os.access("/file/path/foo.txt", os.R_OK):
    print "File is accessible to read"
if os.access("/file/path/foo.txt", os.W_OK):
    print "File is accessible to write"
if os.access("/file/path/foo.txt", os.X_OK):
    print "File is accessible to execute"

2. Use the Try statement

You can use the open() method directly in the program to check whether the file exists and is readable and writable.

Syntax:

open()

If the file you open does not exist, the program will throw an error, use the try statement to catch this error.

The program cannot access the file. There may be many reasons:

If the file you open does not exist, a FileNotFoundError exception will be thrown;

The file exists, but there is no permission. Access will throw a PersmissionError exception.

So you can use the following code to determine whether the file exists:

try:
    f =open()
    f.close()
except FileNotFoundError:
    print "File is not found."
except PersmissionError:
    print "You don't have permission to access this file."

In fact, there is no need to handle each exception in such detail. The above two exceptions are subclasses of IOError. So you can simplify the program:

try:
    f =open()
    f.close()
except IOError:
    print "File is not accessible."

Use the try statement to make judgments and handle all exceptions very simply and elegantly. And compared with others, there is no need to introduce other external modules.

3. Use the pathlib module

The pathlib module is a built-in module in the Python3 version, but in Python2, third-party modules need to be installed separately.

Using pathlib requires first using the file path to create a path object. This path can be a file name or a directory path.

Check if the path exists

path = pathlib.Path("path/file")
path.exist()

Check if the path is a file

path = pathlib.Path("path/file")
path.is_file()

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