Relative import between modules

Question

I've written a group of functions that I wanted to use for my computation and I've organize them in some .py file, say functions1.py and functions2.py. Within the same folder I have also another file main.py, then:

root\ 
- functions1.py
- functions2.py 
- main.py

---

Inside functions1.py suppose I have the following code:

import numpy as np

def mycos(x): 
    return np.cos(x)

def mysin(x):
    return np.sin(x)

While inside functions2.py:

from .functions1 import mysin, mycos

def mytan(x):
    return mysin(x)/mycos(x)

---

Now suppose that main.py contain:

import numpy as np
from .functions2 import mytan

angle = np.pi/3
if mytan(angle) == np.tan(angle):
    print('OK')

Then, If I execute main.py I got the following error:

Traceback (most recent call last):
  File "functions2.py", line 6, in <module>
    from .functions1 import mysin, mycos
ImportError: attempted relative import with no known parent package

Did I miss something in the use of relative import?

Answer 1

i think this is because when you run the code you are not executing in the project directory, try adding these few lines at the beginning of the code of main.py

import os # don't add this line if you have already imported os
os.chdir(os.path.dirname(os.path.abspath(__file__)))

let me know if this works, if it doesn't... can you share the full code to understand better your problem?

---

EDIT
the problem should be that the file functions1.py and functions2.py are not actually modules, to fix this i am gonna suggest you two solutions:

---

Create a folder

as the two function file are not taken as a module, create a folder and put them inside it like so

MAINDIR
– main.py
– functions
–– functions1.py
–– functions2.py

the code is this

main.py

import numpy as np
from functions.functions2 import mytan

angle = np.pi/3
if mytan(angle) == np.tan(angle):
    print('OK')

functions1.py

import numpy as np

def mycos(x):
    return np.cos(x)

def mysin(x):
    return np.sin(x)

functions2.py

from .functions1 import mysin, mycos

def mytan(x):
    return mysin(x)/mycos(x)

---

Use __init__.py

MAINDIR
– main.py
– functions
–– __init__.py
–– functions1.py
–– functions2.py

and this is the code

init.py

import functions1, functions2

(and all other files just like the first solution)
note that this solution is a bit longer, but this should be the most "correct" way to do this

And then?

if you wanna understand better why it wasn't working i would like to suggest you to read this well done articles:
real python
geeks for geeks

Cheers J.Bloom