try/exception using isfile

[paul18fr]

Hi,

I'm just wondering if it's possible to use an exception with isfile without opening it (ot course it/then/else do the job): just a reflexion

try:
    os.path.isfile(os.path.join(os.getcwd(), 'file.txt'))
    # open(os.path.join(os.getcwd(), 'file.txt'), 'r')
    
except FileNotFoundError:
    print("file not found")

[Axel_Erfurt]

try:
    with open('file.txt', 'r') as f:
        print("file found")
except FileNotFoundError:
    print("file not found")

[snippsat]

Your code won't work as expected because os.path.isfile() doesn't raise a FileNotFoundError exception,
it simply returns True or False.
So for simple existence checks:

filepath = os.path.join(os.getcwd(), 'file.txt')
if os.path.isfile(filepath):
    # File exists
    pass
else:
    print("file not found")

Code over only check if File exists and raise exception for other errors,
A better appoch coud be using pathlib with exceptions (EAFP approach):

from pathlib import Path

path = Path.cwd() / "file.txt"
try:
    with path.open("r", encoding="utf-8") as f:
        for line in f:
            print(line.rstrip())
except OSError as e:
    # Any OS-level I/O failure (missing file, perms, dir vs file, etc.)
    print(f"I/O error: {e}")

Or maybe give a own print messag for each error,to make it clearer.

from pathlib import Path

path = Path.cwd() / "file.txt"
try:
    with path.open("r", encoding="utf-8") as f:
        for line in f:
            # do stuff with the line
            print(line.rstrip())
except FileNotFoundError:
    print(f"file not found: {path}")
except IsADirectoryError:
    print(f"path is a directory: {path}")
except PermissionError:
    print(f"no permission to read: {path}")
except OSError as e:
    # covers other I/O problems (e.g., too many open files, invalid name)
    print(f"I/O error: {e}")

[paul18fr]

ok, my question is stupid: either we use the exception and we've to open the file, either with use isfile but without the exception: both cannot be used at the same time

Thanks

[snippsat]

Yes, Path.is_file() or os.path.isfile returns a boolean and won’t raise FileNotFoundError,
Ok for simple if/else test,not for exception-driven flow.
Simplest form.

from pathlib import Path

if (Path.cwd() / "file.txt").is_file():
    print("file found:")
else:
    print("file not found:")

If look at more complete exampes and read a little about LBYL vs EAFP.
look before you leap (LBYL)

from pathlib import Path

path = Path.cwd() / "file.txt"
if not path.exists():
    print("file not found")
elif path.is_dir():
    print("path is a directory")
else:
    with path.open("r", encoding="utf-8") as f:
        for line in f:
            print(line.rstrip())

easier to ask forgiveness than permission (EAFP)

from pathlib import Path

path = Path.cwd() / "file.txt"
try:
    with path.open("r", encoding="utf-8") as f:
        for line in f:
            print(line.rstrip())
except OSError as e:
    # Any OS-level I/O failure (missing file, perms, dir vs file, etc.)
    print(f"I/O error: {e}")

[DeaD_EyE]

Checking whether a resource is the available, is the wrong approach.

Simple example:

1. Your program checks whether a path is a file.
   
2. Result: True.
   
3. Another process deletes the file.
   
4. Your program tries to open the file and then throws an exception.
   

Your program only knows whether it can open a file without errors when it tries to open the file.