Call a function from another file?

Question

Set_up: I have a .py file for each function I need to use in a program.

In this program, I need to call the function from the external files.

I've tried:

from file.py import function(a,b)

But I get the error:

ImportError: No module named 'file.py'; file is not a package

How do I fix this problem?

Solution 1

There isn't any need to add file.py while importing. Just write from file import function, and then call the function using function(a, b). The reason why this may not work, is because file is one of Python's core modules, so I suggest you change the name of your file.

Note that if you're trying to import functions from a.py to a file called b.py, you will need to make sure that a.py and b.py are in the same directory.

Solution 2

First of all you do not need a .py.

If you have a file a.py and inside you have some functions:

def b():
  # Something
  return 1

def c():
  # Something
  return 2

And you want to import them in z.py you have to write

from a import b, c

Solution 3

If your file is in the different package structure and you want to call it from a different package, then you can call it in that fashion:

Let's say you have following package structure in your python project:

in - com.my.func.DifferentFunction python file you have some function, like:

def add(arg1, arg2):
    return arg1 + arg2

def sub(arg1, arg2) :
    return arg1 - arg2

def mul(arg1, arg2) :
    return arg1 * arg2

And you want to call different functions from Example3.py, then following way you can do it:

Define import statement in Example3.py - file for import all function

from com.my.func.DifferentFunction import *

or define each function name which you want to import

from com.my.func.DifferentFunction import add, sub, mul

Then in Example3.py you can call function for execute:

num1 = 20
num2 = 10

print("\n add : ", add(num1,num2))
print("\n sub : ", sub(num1,num2))
print("\n mul : ", mul(num1,num2))

Output:

 add :  30

 sub :  10

 mul :  200

Solution 4

You can do this in 2 ways. First is just to import the specific function you want from file.py. To do this use

from file import function

Another way is to import the entire file

import file as fl

Then you can call any function inside file.py using

fl.function(a,b)

Solution 5

You can call the function from a different directory as well, in case you cannot or do not want to have the function in the same directory you are working. You can do this in two ways (perhaps there are more alternatives, but these are the ones that have worked for me).

Alternative 1 Temporarily change your working directory

import os

os.chdir("**Put here the directory where you have the file with your function**")

from file import function

os.chdir("**Put here the directory where you were working**")

Alternative 2 Add the directory where you have your function to sys.path

import sys

sys.path.append("**Put here the directory where you have the file with your function**")

from file import function

View more solutions

Comments

[user2977230]

The "file" was just a placeholder for the question I am asking, not the actual file name. Thank you though. I will try this and get back to you.

[m3nda]

I don't know if my fail is about python versions. What i do choosing this example is import fn (without extension) and using them directly on the main file fn.my_funcion(). When i use import fn.py tries to load py.py file, wich doesn't exist. Using from fn.py import funcname didn't work too. Thank you.

[DarkRose]

I tried this, but it is still showing the error: Has it got anything to do with Python 3, or is a general problem?

[Dimitar Marinov]

you can also import *

[Tom]

@GamesBrainiac, what if the file you want to import functions from is in a different directory? Can I include the filepath preceeding the filename, or is there something more complicated?

[Games Brainiac]

@Tom You have to add that path to the PYTHONPATH variable if it is not already in there.

[Nirvan Sengupta]

Is there a way to import functions from a.py to a file b.py if they are not in the same directory?

[Karlo]

@DimitarMarinov With * replaced by the filename?

[Dimitar Marinov]

@Karlo, no, just *

[Francisco Gutiérrez]

using "import *" is considered a bad practice. Explicit is better than implicit.

[Mohan]

Oh sure it doesn't. I didn't meant to type .py It's a typo

[Jason]

newbies try "import file", which should execute only once (singleton)

[Aditya C]

If a.py is in a folder say fol1, then how shall it be imported? @dimitar-marinov

[GoodDeeds]

@AdityaC add the folder to your PYTHONPATH is one way

[quantik]

Do you have to import all dependencies from file that are used in function as well?

[alex]

In Python 2 it looks like this either (a) executes the entire script you're referencing with from foo import ... or (b) does not work if foo.py has references to the argparse library.

[Birish]

isn't it the same as adding path to PYTHONPATH?

[jdhao]

glob import is discouraged.

[duXing]

Dimitar Marinov means this: from a import *

[JeffCharter]

I don't think you can have . or - in the file names

[0xc0de]

Can't resist to point out the Java like file structure... com.my.example.. kinda pokes into my eyes, though it might be just me.

[abanmitra]

:)...actually I am from a java background

[Pe Dro]

WHat should be the working directory to run the code ?

[abanmitra]

I am executing this addition or multiplication function from the "Example3.py" file.

[Pieter21]

This is the one that worked for me in a special case where I wanted to 'borrow-call' some external code without copy or modification.

[Antti]

I would rate this a correct answer. Concise and clear solution.

[Haha]

Any explanation about this please ?

[Shubh]

saved my day, thanks . '.' points to current working directory

[nuKs]

@DarkRose Same for me, I fixed it by changing the order of the imports within init.py file, making sure root dependencies were loaded after their transitive dependencies.

[PatrickT]

Didn't work with a hyphen in the filename, e.g. from fil-e import *.

[Shiri]

@jdhao Thanks for the constructive alternative.