What importing a file means in Python

Importing a file in Python means loading code from another file so you can use it in the file you are working on right now. When you import, Python reads that other file, runs any setup code in it, and makes its functions, variables, and classes available to your current script. This saves you from rewriting the same code over and over.

Python has three main ways to import: you can import an entire file (called a module), import specific pieces from a file, or import a file under a different name. Which one you use depends on what code you need and how much of it you want to bring in.

Key Takeaways

  • The import statement loads a Python file so you can use the functions and variables inside it.
  • A module is just a Python file with a .py extension that contains code you want to reuse.
  • You can import an entire module, import only specific functions, or import a module under a shorter name to type less.
  • Python looks for imported files in specific folders on your computer, and you may need to move your file to the right location for Python to find it.
  • The most common import error happens when Python cannot find the file you are trying to import, usually because it is in the wrong folder.

The three ways to import a file

The simplest import is import modulename. If you have a file called math_tools.py that contains a function called add_numbers, you would write import math_tools at the top of your script. Then you call the function by typing math_tools.add_numbers(5, 3). You have to use the module name every time, which is longer but makes it clear where the function came from.

The second way is from modulename import functionname. Using the same example, you would write from math_tools import add_numbers. Now you can call it directly as add_numbers(5, 3) without typing the module name first. This is shorter to type but less clear about where the function lives.

The third way is import modulename as shortname. You would write import math_tools as mt, then call mt.add_numbers(5, 3). This is useful when a module name is long or when you are importing multiple modules and want to keep the names short and distinct.

Where Python looks for files to import

When you write an import statement, Python does not search your entire computer. It looks in specific folders in a specific order. First, it checks the folder where your current script is located. Then it checks a list of standard folders where Python keeps its built-in modules. You can see this list by typing import sys and then print(sys.path) in your script.

If the file you want to import is in the same folder as your script, Python finds it when ready. If it is in a different folder, you have two options: move the file to the same folder as your script, or add the folder to Python's search path using sys.path.append(). The first option is simpler for beginners.

Importing from the Python standard library

Python comes with hundreds of built-in modules that you can import without installing anything. Common ones include math (for mathematical functions), random (for generating random numbers), datetime (for working with dates and times), and os (for interacting with your operating system). You import these the same way you import your own files: import math or from random import choice.

These modules are already on your computer because they came with Python. You do not need to read them or put them in a special folder. This makes them the easiest way to start learning about imports.

Importing files you downloaded or installed

When you read a Python package from the internet or install one using a tool called pip, the files go into a special folder that Python knows to search. For example, if you install a package called requests (used for downloading web pages), you can import it with import requests even though you did not write it yourself.

To install a package, you open your computer's command line (Terminal on Mac, Command Prompt on Windows) and type pip install packagename. Python downloads the package and puts it in the right place automatically. After that, you can import it in any script on your computer.

The most common import errors and how to fix them

The error ModuleNotFoundError: No module named 'modulename' means Python looked in all its search folders and could not find the file. If you are importing your own file, check that the .py file is in the same folder as your script and that you spelled the name correctly (Python is case-sensitive). If you are importing a downloaded package, check that you installed it with pip and spelled the name right.

Another common mistake is forgetting the .py extension. You write import math_tools, not import math_tools.py. Python adds the extension automatically when it searches.

If you see ImportError: cannot import name 'functionname', it means Python found the module but could not find that specific function inside it. Check that the function exists in the file you are importing from and that you spelled it correctly.

Organizing your code with imports

As your Python projects grow, you will write more and more code. Imports let you split that code into separate files organized by what they do. You might have one file for functions that work with numbers, another for functions that work with text, and another for functions that talk to a database. Your main script then imports from all three.

This makes your code easier to read, easier to test, and easier to reuse in other projects. A function you write once can be imported into ten different scripts. If you need to fix a bug in that function, you fix it in one place and all ten scripts benefit.

Frequently Asked Questions

Can I import a file that is in a different folder?

Yes. The simplest way is to move the file to the same folder as your script. If you cannot do that, you can add the folder to Python's search path using sys.path.append('/path/to/folder') at the top of your script, replacing the path with the actual location of the folder.

What is the difference between import and from import?

import modulename loads the entire module and you access its contents by typing the module name first (like modulename.function()). from modulename import functionname loads only that specific function and you can call it directly. Use the first when you need many things from a module; use the second when you need only one or two.

Do I need to install Python packages to import them?

Only if they are not built-in. Modules that come with Python (like math, random, and datetime) are already installed. Packages you read from the internet must be installed first using pip install packagename in your command line.

What does "ModuleNotFoundError" mean?

It means Python looked for the file you tried to import but could not find it. Check that the file is in the same folder as your script, that you spelled the name correctly (including uppercase and lowercase letters), and that the file ends in .py. If you are importing a downloaded package, check that you installed it with pip.

Can I import the same file twice in one script?

Python only imports a file once, even if you write the import statement multiple times. The first time it runs the file and loads everything; the second time it skips the file and uses what it already loaded. This prevents code from running twice and keeps your script efficient.