Modules and Imports
As your programs get larger, it's good practice to split your code into multiple files. In Python, each file is considered a "module". You can use the import statement to use functions, classes, and variables from one module in another.
Basic Import
Let's say you have a file named my_math.py:
# my_math.py
def add(a, b):
return a + b
PI = 3.14159
You can import this module in another file, like main.py, to use its contents.
# main.py
import my_math
result = my_math.add(5, 3)
print(result) # => 8
print(my_math.PI) # => 3.14159
Specific Imports
You can also import specific functions or variables from a module using the from keyword.
from my_math import add, PI
result = add(10, 20)
print(result) # => 30
print(PI) # => 3.14159
You can also use * to import everything, but this is generally discouraged as it can lead to naming conflicts.
from my_math import *
Aliasing
You can rename a module or an imported function using the as keyword. This is useful for shortening long names or avoiding conflicts.
import my_math as mm
from my_math import add as addition
result = mm.add(2, 2)
print(result) # => 4
result2 = addition(1, 1)
print(result2) # => 2
The if __name__ == "__main__" block
Sometimes you want to have code in a file that runs only when that file is executed directly, not when it's imported as a module. You can do this by placing that code inside an if __name__ == "__main__" block.
When you run a Python file directly, Python sets the special variable __name__ for that file to "__main__". When the file is imported, __name__ is set to the module's name (the filename).
# my_math.py
def add(a, b):
return a + b
# This code will only run when my_math.py is executed directly
if __name__ == "__main__":
print("Running my_math.py as a script!")
print(add(10, 5))
If you run python my_math.py, it will print:
Running my_math.py as a script!
15
If you import it from main.py, that block will not run.
