Python – How to change/choose the file path in Python

pythonpython-3.x

I'm trying to access a .txt file in Python and I can't figure out how to open the file. I ended up copying the contents into a list directly but I would like to know how to open a file for the future.

If I run this nothing prints. I think it's because Python is looking in the wrong folder/directory but I don't know how to change file paths.

sourcefile = open("CompletedDirectory.txt").read()
print(sourcefile)

Best Answer

The file CompletedDirectory.txt is probably empty.

If Python could not find the file, you would get a FileNotFoundError exception:

>>> sourcefile = open("CompletedDirectory.txt").read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: 'CompletedDirectory.txt'

Note that using read() in this way is not recommended. You're not closing the file properly. Use a context manager:

with open("CompletedDirectory.txt") as infile:
    sourcefile = infile.read()

This will automatically close infile on leaving the with block.

Related Solutions

Python – How to check whether a file exists without exceptions

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

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)

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

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

Python – How to execute a program or call a system command

Use the subprocess module in the standard library:

import subprocess
subprocess.run(["ls", "-l"])

The advantage of subprocess.run over os.system is that it is more flexible (you can get the stdout, stderr, the "real" status code, better error handling, etc...).

Even the documentation for os.system recommends using subprocess instead:

The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in the subprocess documentation for some helpful recipes.

On Python 3.4 and earlier, use subprocess.call instead of .run:

subprocess.call(["ls", "-l"])

Best Answer

Related Solutions

Python – How to check whether a file exists without exceptions

Python – How to execute a program or call a system command

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