Python FileNotFoundError when using open()

Question

I'm using with open('myFile', 'rb') as file: to read a file. When running the program with python myProgram.py everything works fine. But as soon I try to run it without cd-ing into the directory of myProgram.py and use an absolute path instead (like python /home/myName/myCode/myProgram.py I always get this error message: FileNotFoundError: [Errno 2] No such file or directory.

So why does open() behave differently depending on how the Python program is started? And is there a way to make things work even if starting with an absolute path?

I've already tried open('/home/myName/myCode/myfile', 'rb') but without success...

run 'pwd' in the directory where you are able to run the program. post results. — WildCard
– WildCard, Commented May 25, 2016 at 17:53
The file is in the same directory as the python program. WHen I runpwd in the directory where the program works it returns /home/myName/myCode. So that's exactly the directory where both my program and the file are. — lsgng
– lsgng, Commented May 25, 2016 at 18:13
The current working directory of a process and the directory that contains the script are not necessarily the same thing. — chepner
– chepner, Commented May 25, 2016 at 18:25

0x5453 · Accepted Answer · 2016-05-25 18:10:46Z

4

So why does open() behave differently depending on how the Python program is started? And is there a way to make things work even if starting with an absolute path?

Because that is standard behavior. Not just for Python, but for all applications (at least all that I know of). A relative path (like 'myfile') is assumed to be in the current directory. That path will change depending on what directory you are sitting in when you launch the script from a shell. If you don't give an absolute path, how would Python know which file to use in a directory structure like this?

root
|-- dir1
|   `-- myFile
`-- dir2
    `-- myFile

You were on the right track with open('/home/myName/myCode/myfile', 'rb').

answered May 25, 2016 at 18:10

0x5453

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1 Comment

lsgng Over a year ago

Thank you, this completely makes sense. I tried again with open('/home/myName/myCode/myfile', 'rb') and now it's working!

chepner · Accepted Answer · 2016-05-25 18:28:31Z

1

Let's say you run pwd and it returns /home/myName. If you then run /home/myName/code/myProgram.py, the working directory of your program is not /home/myName/code; it's /home/myName. The working directory of a process in inherited from the parent process, not set based on where the script is located.

answered May 25, 2016 at 18:28

chepner

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