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How to read a file in Python function and call that function from some other python file?

Folder structure:
MainFolder
__init__.py
FolderA
Config.json
ConfigHelper.py
testA.py
FolderB
Test.py
ConfigHelper.py file:
import json
class ConfigHelper:
def read_config(self):
fileName = "Config.json"
with open(fileName, "r") as jsonfile:
return json.load(jsonfile)
When calling ConfigHelper.read_config() function from FolderB-->Test.py file , then
Getting Error: No such file or directory: 'config.json'
But if calling it from TestA.py file, No error is coming.
Look like it is taking path relative from the calling place.
Please tell me , How I can fix it?

When you are in FolderB there is no config.json file there.
Solutions
Run your script from MainFolder and pass correct path (FolderA/config.json).
Add folders to path, see.
Change working directory to FolderB before trying to read config.json, see.

You need to provide the full path to the file. You are right that it is looking for the relative path. When you are just passing the Config.json path it is looking in your current working directory for this.

path = os.getcwd()
print("Current Directory", path)
filepath = path + "/MainFolder/FolderA/Config.json"
Gave Full Path as above to fix the problem.

How to read a file in a module by its relative path to the module?

The directory structure:
├--- mod
| ├--- __init__.py
| └--- abc.data
└--- test.py
__init__.py:
with open("abc.data", 'r') as f:
pass # read and process the data
test.py:
import mod
The program above is expected to read the data in the file abc.data, but it gives an error instead:
FileNotFoundError: [Errno 2] No such file or directory: 'abc.data'
And this is because the current directory of Python interpreter is the parent directory of test.py.
So how to read abc.data in the module mod regardless of the location of test.py?
Actually the following code works:
__init__.py:
import os
filepath = os.path.join(os.path.dirname(os.path.realpath(__file__)), "abc.data")
with open(filepath, 'r') as f:
pass # read and process the data
But this solution is a bit dirty especially when there are many files to be read in __init__.py. Is there a more elegant solution?

I believe that's as good as it gets. Even larger libraries use the same method:
# Extracted From selenium/webdriver/firefox/firefox_profile.py
# ...
if not FirefoxProfile.DEFAULT_PREFERENCES:
with open(os.path.join(os.path.dirname(__file__),
WEBDRIVER_PREFERENCES)) as default_prefs:
FirefoxProfile.DEFAULT_PREFERENCES = json.load(default_prefs)
# ...
Another example:
# Extracted from pipenv/vendor/yaspin/spinners.py
# ...
THIS_DIR = os.path.dirname(os.path.realpath(__file__))
SPINNERS_PATH = os.path.join(THIS_DIR, "data/spinners.json")
# ...
If it was an importable object (e.g. .py files) then you can use . conventions to indicate the relative path.

Python - How to open a file inside a module?

I've something like this in my program:
A main script main.py inside a folder named 'OpenFileinaModule'. There's a folder called 'sub' inside it with a script called subScript.py and a file xlFile.xlsx, which is opened by subScript.py.
OpenFileinaModule/
main.py
sub/
__init__.py (empty)
subScript.py
xlFile.xlsx
Here is the code:
sub.Script.py:
import os, openpyxl
class Oop:
def __init__(self):
__file__='xlFile.xlsx'
__location__ = os.path.realpath(
os.path.join(os.getcwd(), os.path.dirname(__file__)))
print os.path.join(__location__, __file__)
self.wrkb = openpyxl.load_workbook(os.path.join(__location__,
__file__),read_only=True)
main.py:
import sub.subScript
objt=sub.subScript.Oop()
When I execute main.py, I get the error:
IOError: [Errno 2] No such file or directory: 'C:\\Users\\...\\OpenFileInaModule\\xlFile.xlsx'
It jumps the sub folder...
I've tried
__file__='sub/xlFile.xlsx'
But then the "sub" folder is duplicated:
IOError: [Errno 2] No such file or directory: 'C:\\Users\\...\\OpenFileInaModule\\sub\\sub/xlFile.xlsx'
How to open xlFile.xlsx with subScript.py from main.py?

you're overriding __file__ with __file='xlFile.xlsx', do you mean to do this?
I think you want something like
import os
fname = 'xlFile.xlsx'
this_file = os.path.abspath(__file__)
this_dir = os.path.dirname(this_file)
wanted_file = os.path.join(this_dir, fname)
I'd suggest always using the absolute path for a file, especially if you're on windows when a relative path might not make sense if the file is on a different drive (I actually have no idea what it would do if you asked it for a relative path between devices).

Please avoid using __file__ and __location__ to name your variables, these are more like builtin variables which might cause a confusion.
Note something here:
__location__ = os.path.realpath(
os.path.join(os.getcwd(), os.path.dirname(__file__)))
You have not included sub directory and the above joins only the CWD + os.path.dirname(__file__). This doesn't get you to the file. Please read the documentation of os.path.dirname: os.path.dirname(__file__) returns an empty string here.
def __init__(self):
file = 'xlFile.xlsx'
location = os.path.join('sub', file)
location = os.path.abspath(location) # absolute path to file
location = os.path.realpath(location) # rm symbolic links in path
self.wrkb = openpyxl.load_workbook(location)

Reading a file using a relative path in a Python project

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 don’t get any 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?

Relative paths are relative to current working directory.
If you do not want your path to be relative, it must be absolute.
But there is an often used trick to build an absolute path from current script: use its __file__ special attribute:
from pathlib import Path
path = Path(__file__).parent / "../data/test.csv"
with path.open() as f:
test = list(csv.reader(f))
This requires python 3.4+ (for the pathlib module).
If you still need to support older versions, you can get the same result with:
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))
[2020 edit: python3.4+ should now be the norm, so I moved the pathlib version inspired by jpyams' comment first]

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)]

This worked for me.
with open('data/test.csv') as f:

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 the 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 reason 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.

Try
with open(f"{os.path.dirname(sys.argv[0])}/data/test.csv", newline='') as f:

I was surprised when the following code worked.
import os
for file in os.listdir("../FutureBookList"):
if file.endswith(".adoc"):
filename, file_extension = os.path.splitext(file)
print(filename)
print(file_extension)
continue
else:
continue
So, I checked the documentation and it says:
Changed in version 3.6: Accepts a path-like object.
path-like object:
An object representing a file system path. A path-like object is
either a str or...
I did a little more digging and the following also works:
with open("../FutureBookList/file.txt") as file:
data = file.read()

Open file in a relative location in Python

Suppose my python code is executed a directory called main and the application needs to access main/2091/data.txt.
how should I use open(location)? what should the parameter location be?
I found that below simple code will work.. does it have any disadvantages?
file = "\2091\sample.txt"
path = os.getcwd()+file
fp = open(path, 'r+');

With this type of thing you need to be careful what your actual working directory is. For example, you may not run the script from the directory the file is in. In this case, you can't just use a relative path by itself.
If you are sure the file you want is in a subdirectory beneath where the script is actually located, you can use __file__ to help you out here. __file__ is the full path to where the script you are running is located.
So you can fiddle with something like this:
import os
script_dir = os.path.dirname(__file__) #<-- absolute dir the script is in
rel_path = "2091/data.txt"
abs_file_path = os.path.join(script_dir, rel_path)

This code works fine:
import os
def read_file(file_name):
file_handle = open(file_name)
print file_handle.read()
file_handle.close()
file_dir = os.path.dirname(os.path.realpath('__file__'))
print file_dir
#For accessing the file in the same folder
file_name = "same.txt"
read_file(file_name)
#For accessing the file in a folder contained in the current folder
file_name = os.path.join(file_dir, 'Folder1.1/same.txt')
read_file(file_name)
#For accessing the file in the parent folder of the current folder
file_name = os.path.join(file_dir, '../same.txt')
read_file(file_name)
#For accessing the file inside a sibling folder.
file_name = os.path.join(file_dir, '../Folder2/same.txt')
file_name = os.path.abspath(os.path.realpath(file_name))
print file_name
read_file(file_name)

I created an account just so I could clarify a discrepancy I think I found in Russ's original response.
For reference, his original answer was:
import os
script_dir = os.path.dirname(__file__)
rel_path = "2091/data.txt"
abs_file_path = os.path.join(script_dir, rel_path)
This is a great answer because it is trying to dynamically creates an absolute system path to the desired file.
Cory Mawhorter noticed that __file__ is a relative path (it is as well on my system) and suggested using os.path.abspath(__file__). os.path.abspath, however, returns the absolute path of your current script (i.e. /path/to/dir/foobar.py)
To use this method (and how I eventually got it working) you have to remove the script name from the end of the path:
import os
script_path = os.path.abspath(__file__) # i.e. /path/to/dir/foobar.py
script_dir = os.path.split(script_path)[0] #i.e. /path/to/dir/
rel_path = "2091/data.txt"
abs_file_path = os.path.join(script_dir, rel_path)
The resulting abs_file_path (in this example) becomes: /path/to/dir/2091/data.txt

It depends on what operating system you're using. If you want a solution that is compatible with both Windows and *nix something like:
from os import path
file_path = path.relpath("2091/data.txt")
with open(file_path) as f:
<do stuff>
should work fine.
The path module is able to format a path for whatever operating system it's running on. Also, python handles relative paths just fine, so long as you have correct permissions.
Edit:
As mentioned by kindall in the comments, python can convert between unix-style and windows-style paths anyway, so even simpler code will work:
with open("2091/data/txt") as f:
<do stuff>
That being said, the path module still has some useful functions.

I spend a lot time to discover why my code could not find my file running Python 3 on the Windows system. So I added . before / and everything worked fine:
import os
script_dir = os.path.dirname(__file__)
file_path = os.path.join(script_dir, './output03.txt')
print(file_path)
fptr = open(file_path, 'w')

Try this:
from pathlib import Path
data_folder = Path("/relative/path")
file_to_open = data_folder / "file.pdf"
f = open(file_to_open)
print(f.read())
Python 3.4 introduced a new standard library for dealing with files and paths called pathlib. It works for me!

Code:
import os
script_path = os.path.abspath(__file__)
path_list = script_path.split(os.sep)
script_directory = path_list[0:len(path_list)-1]
rel_path = "main/2091/data.txt"
path = "/".join(script_directory) + "/" + rel_path
Explanation:
Import library:
import os
Use __file__ to attain the current script's path:
script_path = os.path.abspath(__file__)
Separates the script path into multiple items:
path_list = script_path.split(os.sep)
Remove the last item in the list (the actual script file):
script_directory = path_list[0:len(path_list)-1]
Add the relative file's path:
rel_path = "main/2091/data.txt
Join the list items, and addition the relative path's file:
path = "/".join(script_directory) + "/" + rel_path
Now you are set to do whatever you want with the file, such as, for example:
file = open(path)

import os
def file_path(relative_path):
dir = os.path.dirname(os.path.abspath(__file__))
split_path = relative_path.split("/")
new_path = os.path.join(dir, *split_path)
return new_path
with open(file_path("2091/data.txt"), "w") as f:
f.write("Powerful you have become.")

If the file is in your parent folder, eg. follower.txt, you can simply use open('../follower.txt', 'r').read()

Get the path of the parent folder, then os.join your relative files to the end.
# get parent folder with `os.path`
import os.path
BASE_DIR = os.path.dirname(os.path.abspath(__file__))
# now use BASE_DIR to get a file relative to the current script
os.path.join(BASE_DIR, "config.yaml")
The same thing with pathlib:
# get parent folder with `pathlib`'s Path
from pathlib import Path
BASE_DIR = Path(__file__).absolute().parent
# now use BASE_DIR to get a file relative to the current script
BASE_DIR / "config.yaml"

Python just passes the filename you give it to the operating system, which opens it. If your operating system supports relative paths like main/2091/data.txt (hint: it does), then that will work fine.
You may find that the easiest way to answer a question like this is to try it and see what happens.

Not sure if this work everywhere.
I'm using ipython in ubuntu.
If you want to read file in current folder's sub-directory:
/current-folder/sub-directory/data.csv
your script is in current-folder
simply try this:
import pandas as pd
path = './sub-directory/data.csv'
pd.read_csv(path)

When I was a beginner I found these descriptions a bit intimidating. As at first I would try
For Windows
f= open('C:\Users\chidu\Desktop\Skipper New\Special_Note.txt','w+')
print(f)
and this would raise an syntax error. I used get confused alot. Then after some surfing across google. found why the error occurred. Writing this for beginners
It's because for path to be read in Unicode you simple add a \ when starting file path
f= open('C:\\Users\chidu\Desktop\Skipper New\Special_Note.txt','w+')
print(f)
And now it works just add \ before starting the directory.

In Python 3.4 (PEP 428) the pathlib was introduced, allowing you to work with files in an object oriented fashion:
from pathlib import Path
working_directory = Path(os.getcwd())
path = working_directory / "2091" / "sample.txt"
with path.open('r+') as fp:
# do magic
The with keyword will also ensure that your resources get closed properly, even if you get something goes wrong (like an unhandled Exception, sigint or similar)