Open all files in different directory python

Question

I need to open a file from a different directory without using it's path while staying in the current directory.

When I execute the below code:

for file in os.listdir(sub_dir):
    f = open(file, "r")
    lines = f.readlines()
    for line in lines:
        line.replace("dst=", ", ")
        line.replace("proto=", ", ")
        line.replace("dpt=", ", ")

I get the error message FileNotFoundError: [Errno 2] No such file or directory: because it's in a sub directory.

Question: Is there an os command I can use that will locate and open the file in sub_dir?

Thanks! -let me know if this is a repeat, I searched and couldn't find one but may have missed it.

Answer 1

os.listdir() lists only the filename without a path. Prepend these with sub_dir again:

for filename in os.listdir(sub_dir):
    f = open(os.path.join(sub_dir, filename), "r")

If all you are doing is loop over the lines from the file, just loop over the file itself; using with makes sure that the file is closed for you when done too. Last but not least, str.replace() returns the new string value, not change the value itself, so you need to store that return value:

for filename in os.listdir(sub_dir):
    with open(os.path.join(sub_dir, filename), "r") as f:
        for line in f:
            line = line.replace("dst=", ", ")
            line = line.replace("proto=", ", ")
            line = line.replace("dpt=", ", ")