Python – py2exe and the file system

configurationfilepy2exepython

I have a Python app. It loads config files (and various other files) by
doing stuff such as:

_path = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
CONFIG_DIR = os.path.join(_path, 'conf')

This works fine. However, when I package the app with py2exe, bad things happen:

  File "proj\config.pyc", line 8, in <module>
WindowsError: [Error 3] The system cannot find the path specified: 'C:\\proj\
\dist\\library.zip\\conf'

Obviously that's an invalid path… What's a more robust way of doing this? I don't
want to specify absolute paths in the program because it could be placed in different
folders. Should I just say "if it says the folder name is 'library.zip', then go
one more level down to the 'dist' folder"?

Note that I have pretty nested directory hierarchies… for example, I have
a module gui.utils.images, stored in "gui/utils/images.py", and it uses its path
to access "gui/images/ok.png", for example. Right now the py2exe version
would try to access "proj/dist/library.zip/gui/images/ok.png", or something,
which just won't work.

Best Solution

What do you think about using relative paths for all of the included files? I guess it should be possible to use sys.path.append(".." + os.path.sep + "images") for your example about ok.png, then you could just open("ok.png", "rb"). Using relative paths should fix the issues with the library.zip file that's generated by py2exe, at least that's what it does for me.

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 Solution

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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