Reading file using relative path in python project

问题

Say I have a python project that is structured as follows:

project
    /data
        test.csv
    /package
        __init__.py
        module.py
    main.py

__init__.py:

from .module import test

module.py:

import csv

with open("..data/test.csv") as f:
    test = [line for line in csv.reader(f)]

main.py:

import package

print(package.test)

When I run main.py I get the following error:

 C:\Users\Patrick\Desktop\project>python main.py
Traceback (most recent call last):
  File "main.py", line 1, in <module>
    import package
  File "C:\Users\Patrick\Desktop\project\package\__init__.py", line 1, in <module>
    from .module import test
  File "C:\Users\Patrick\Desktop\project\package\module.py", line 3, in <module>
    with open("../data/test.csv") as f:
FileNotFoundError: [Errno 2] No such file or directory: '../data/test.csv'

However, if I run module.py from the package directory I get no errors. So it seems that the relative path used in open(...) is only relative to where the originating file is being run from (i.e __name__ == "__main__")? I don't want to use absolute paths. What are some ways to deal with this?

回答1:

Relative paths are relative to current working directory. If you do not your want your path to be, it must be absolute.

But there is an often used trick to build an absolute path from current script: use its __file__ special attribute:

import csv
import os.path

my_path = os.path.abspath(os.path.dirname(__file__))
path = os.path.join(my_path, "../data/test.csv")
with open(path) as f:
    test = list(csv.reader(f))

Note, from python 3.4, __file__ is always absolute for imported modules and you can drop the os.path.abspath part in this example.

Better yet with python 3.4+, use the Path module as jpyams suggested in the comment below:

from pathlib import Path

path = Path(__file__).parent / "../data/test.csv"
with path.open() as f:
    test = list(csv.reader(f))

回答2:

For Python 3.4+:

import csv
from pathlib import Path

base_path = Path(__file__).parent
file_path = (base_path / "../data/test.csv").resolve()

with open(file_path) as f:
    test = [line for line in csv.reader(f)]

回答3:

My Python version is Python 3.5.2 and the solution proposed in the accepted answer didn't work for me. I've still were given an error

FileNotFoundError: [Errno 2] No such file or directory

when I was running my_script.py from the terminal. Although it worked fine when I run it through Run/Debug Configurations from PyCharm IDE (PyCharm 2018.3.2 (Community Edition)).

Solution:

instead of using:

my_path = os.path.abspath(os.path.dirname(__file__)) + some_rel_dir_path

as suggested in the accepted answer, I used:

my_path = os.path.abspath(os.path.dirname(os.path.abspath(__file__))) + some_rel_dir_path

Explanation: Changing os.path.dirname(__file__) to os.path.dirname(os.path.abspath(__file__)) solves the following problem:

When we run our script like that: python3 my_script.py the __file__ variable has a just a string value of "my_script.py" without path leading to that particular script. That is why method dirname(__file__) returns an empty string "". That is also the reson why my_path = os.path.abspath(os.path.dirname(__file__)) + some_rel_dir_path is actually the same thing as my_path = some_rel_dir_path. Consequently FileNotFoundError: [Errno 2] No such file or directory is given when trying to use open method because there is no directory like "some_rel_dir_path".

Running script from PyCharm IDE Running/Debug Configurations worked because it runs a command python3 /full/path/to/my_script.py (where "/full/path/to" is specified by us in "Working directory" variable in Run/Debug Configurations) instead of justpython3 my_script.py like it is done when we run it from the terminal.

Hope that will be useful.

来源：https://stackoverflow.com/questions/40416072/reading-file-using-relative-path-in-python-project

标签

python

python-3.x

relative-path

python-import