Importerror: attempted relative import with no known parent package.

Question

Problem :

I am very new to Python. Now I am trying to import my function from the another file in a same directory. I am able to do it sometimes with the use of .mymodule import myfunction but most of the times I face below error:

“Importerror: attempted relative import with no known parent package”.

I am unable to understand the above error and also couldn't find any relevant explanation about it. It seems completely random to me. I am looking for someone who is expert in Python and who can help me in fixing above error.

Answer 1

I had also faced the same Python error in the past. I also had to spend a lot of time in fixing it. I found a  workaround which is importing with the use of if/else block as shown below:

if __name__ == '__main__':
    from mymodule import as_int
else:
    from .mymodule import as_int

# Exported Add function
def expadd(a, b):
    return as_int(a) + as_int(b)

# Test the function for the module  
def _exptest():
    assert expadd('1', '1') == 2

if __name__ == '__main__':
    _exptest()

If above solution is not working for you and if both of your packages are in the import path (i.e. sys.path), and your module or class you want is in the example/example.py, then to access your class without the relative import you can try:

from example.example import fkt

Answer 2

unfortunately, this module requires to be within the package, and it also requires to be runnable as a script, occasionally. Any idea how I could achieve that?

It's quite usual to have a layout like this

main.py
mypackage/
    __init__.py
    mymodule.py
    myothermodule.py

.with a mymodule.py like this

#!/usr/bin/env python3

# Exported function
def as_int(a):
    return int(a)

# Test function for module  
def _test():
    assert as_int('1') == 1

if __name__ == '__main__':
    _test()

..a myothermodule.py like this…

#!/usr/bin/env python3

from .mymodule import as_int

# Exported function
def add(a, b):
    return as_int(a) + as_int(b)

# Test function for module  
def _test():
    assert add('1', '1') == 2

if __name__ == '__main__':
    _test()

..and a main.py like this…

#!/usr/bin/env python3

from mypackage.myothermodule import add

def main():
    print(add('1', '1'))

if __name__ == '__main__':
    main()

...which performs fine at the time you run main.py or mypackage/mymodule.py, however fails with mypackage/myothermodule.py, due to the relative import…

from .mymodule import as_int

The way you're inferred to run it is…

python3 -m mypackage.myothermodule

however it's somewhat verbose, and doesn't mix well with a shebang line like #!/usr/bin/env python3.

The easiest solve for this instance, pretending the name mymodule is globally unique, would be to avoid employing relative imports, and just use…

from mymodule import as_int

Though, in case it's not unique, or your package structure is more complex, you'll require to add the directory bearing your package directory in PYTHONPATH, and do it like this…

from mypackage.mymodule import as_int

...or in case you want it to perform "out of the box", you can frob the PYTHONPATH in code first with this…

import sys
import os

PACKAGE_PARENT = '..'
SCRIPT_DIR = os.path.dirname(os.path.realpath(os.path.join(os.getcwd(), os.path.expanduser(__file__))))
sys.path.append(os.path.normpath(os.path.join(SCRIPT_DIR, PACKAGE_PARENT)))

from mypackage.mymodule import as_int

I'm -1 on this and on any other raised twiddlings of the __main__ machinery. The only employ instance appears to be running scripts that occur to be living within a module's directory, which I've always view as an antipattern. To make me change my mind you'd have to convince me that it isn't.

Whether running scripts within a package is an antipattern or not is subjective, however personally I trace it truly helpful in a package I have which comprise few custom wxPython widgets, so I can run the script for any of the source files to display a wx.Frame bearing just that widget for testing purposes.

Answer 3

Whenever you get an error produced by the interpreter or compiler read it carefully. The error message says all about the cause of encountered error in a nutshell. You are having an ImportError in this case. As you’ve mentioned, you are trying to import a user-defined function from another file within the same directory. Let me give an example. Assume you have a file named foo.py that contains below functions:

def function():
	# do something herea
	return 1
def another_function():
	# do something herea
	return 2

And now, you want to import the file in bar.py as a module to use the functions available in foo.py. You should simply do:

from foo import function, another_function

Yes! It is as simple as this. This has to be work all you need to make sure that the files are in the same directory. Good day!