How do I call a function from another .py file?

Steer clear of module naming collisions

In Python, naming is crucial. When you import a file, Python uses the name to locate the right module. If the file's name matches one in Python's standard library, you'll get a naming conflict. Conflicts can cause strange behavior and bugs.

# NOT ok: will import Python's in-build math module, not your file
import math

# OK: unique name, no collision
import my_math_functions
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Remember: unique names, you'll save headaches 😊

Different Flavors of Imports

Python's import system is flexible. We can import individual functions like we've seen or import the entire file as a module and reference functions using the filename. This is called module importation.

import other_file
other_file.function_name()
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You can even simplify module names with the as keyword.

# Importing... Renaming to avoid typographical strain 😜
import other_file as of
of.function_name()
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Location, Location, Location!

By default, Python will search for files to import in the current directory. If other_file.py isn't in the current directory, Python's sys.path can help out.

import sys
# Adding a directory to Python's "list" of searchable directories
sys.path.append("/path/to/your/file_directory")
from other_file import function_name
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You can also switch to the import file's directory using os.

import os

os.chdir("/path/to/your/file_directory")  # Switch directories
from other_file import function_name      # Import after switch

# If necessary, switch back to the original directory.
os.chdir("/path/to/your/original_directory")
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Remember, Python's like a dog—it needs directions! 🐶

Diving into Packages

If you've neatly organized your code using packages (directories containing an __init__.py file), you'll need to reflect this in your import statement.

from package.subpackage.other_file import function_name
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Relative and absolute imports ensure smooth navigation of your code's maritime trade routes when dealing with complex directory structures.

Making the Correct Function Call

After calling card to import, make sure you use the correct function names and arguments. Now, you can call that imported function as if it was one of your locals—you've given it a visa!

from other_file import function_name as fn
fn()  # Easier name to use
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Dynamically Importing Functions

The importlib library allows importing dynamically—right when you need it. This dynamic import feature is perfect if you don't know which file to import from ahead of time.

from importlib import import_module

dynamic_file = import_module('dynamic_file_name')
dynamic_file.dynamic_function()  # Operation successful!! 🚀
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Breaking Circular Imports

You might face a circular import situation—two modules importing each other. This can mess up initialization order, causing problems. To remedy this:

1. Rearrange your code to eliminate circular dependencies.
2. Delay the import by moving it within a function.
3. Import the entire module and use dot syntax to reference functions.

def some_function():
    import problem_module  # Delay import
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"An import a day** keeps the circular imports away!" 🍏