Imagine if you're a data scientist and you have a number of common preprocessing scripts that you want to run on data and you simply want to keep those on your system and you want to be able to call them whenever you're working on programs in the repl.

That is a very common convention and a helpful tool. However, there is also another use case for importing and that is when you're building out your own programs and you want to call one of your modules from another file. And so that's what we're going to walk through in this guide. We're going to see how we can create a custom module just like we have right here with our helper.py file and our greeter function.

Then we are going to create another file and then import it directly in, later on in the guide we're going to expand our knowledge, and we're also going to see how we can call our helper functions from outside of the current directory. And so we're going to cover all of that in this guide. Let's first go with the base case and so what we're going to do is create a new file here.

It's going to be called main.py y I'm going to save this file and if I come and refresh the tree here on the left-hand side you can see we have a main.py file.

Now, in order to import this, it's actually the exact same syntax that we used for the repl so I can say import helper. So what Python is going to do by default is it's going to look inside of the current directory and it's going to look for a helper.py file and then it's going to import that module and the functions inside of it. So I'm going to import the helper and then I'm going to create a function called render and it's not gonna take any arguments and from there I'm simply going to print out helper.greeting and then pass in the string, so I'll say 'Tiffany', 'Hudgens' and that's all I need to do.

helper.py

def render():
  print(helper.greeting('Tiffany', 'Hudgens'))

main.py

def greeting(first, last):
  return f'Hi {first} {last}'

I'm also going to call this render function so that it runs automatically whenever the main file is called. And now if I open up the terminal right inside this directory and that is a very key if you're running this script make sure that you are inside of whatever directory. Both of these files and MCSA python and then main. Why. And if I run this you can see that it works perfectly.

It went, it grabbed the helper module it brought it into the main file, and then it had access to the greeting function. So far everything is looking really good. Now, that is what happens whenever you want to import a helper module or any kind of module directly within the same directory.

However, many times you're going to want to keep all of your scripts in different directories and so when you want to do that you have to add a few more steps and so I'm going to recreate that by creating a directory here called lib's and then I'm going to move our helper module into the Libs directory. So everything's going to be identical except now if I come down and hit refresh you can see that I have a lib's directory and that is where the helper.py file is located.

Now if I go into main and I don't make any changes and try to run this you're going to see that we run into an error. So if I run this you can see it gives the error that inside of the main.py file on line 1 for import helper the module was not found.

The reason for that goes directly to the default behavior of how python import's modules. Whenever you're using this kind of syntax import helper python is going to look at the default set paths so it's going to look inside of the current directory and then it's also going to look and see any third-party packages that you've imported because those by default get added to the python import path.

Now in order to have our own custom set of modules accessible we're going to have to work with the system so we're going to add a couple more lines here. We're going to first import the system library. Now, this is directly available to us inside of the Python language, and then from here, we're going to add a new path. So we simply need to take our libs directory and add it to the path that Python looks for whenever it's looking for modules that it can import.

So here I can say sys.path.insert and then pass in first the place where in the path I want this accessible. So what insert is going to do is it's going to take the full list of paths that Python looks at, and it's going to say at the very first spot I want you to insert this new path. This is only going to be set for this current file, it's not going to affect any other programs that you have on your system and then the second argument is the path itself.

Now if this file is located exactly where we have it you can't simply call lib's instead we have to explicitly say './libs' and what that's going to do is it's going to tell python that I want you to look inside of the working directory where we're at and then look for a directory called lib's and then it's going to insert that path. So I'm gonna save this file. And now we're going to try to rerun this code and if I run this now you can see that it is working properly.

So congratulations if you went through that you now know how to create a custom python module call it from either the current directory that your other files are in or even a directory somewhere else on your system entirely.

Code

# libs/helper.py file
def greeting(first, last):
    return f'Hi {first} {last}!'

# main.py file
import sys
sys.path.insert(0, './libs')
import helper

def render():
    print(helper.greeting('Kristine', 'Hudgens'))


render()