ይህ ትምህርት ገና ወደ አማርኛ አልተተረጎመም፤ ስለዚህ በእንግሊዝኛ ቀርቧል። የእንግሊዝኛውን ገጽ ክፈቱ

Modules and imports

4 min read

Your programs are getting long, and some functions, like a VAT calculation, are useful in more than one of them. By the end of this lesson you'll split a program into files, import your own functions from another file, and finally understand the if __name__ == "__main__": line from lesson 5.8.

A file other files can use

Any Python file is a modulemoduleA Python file whose functions and names other files can use, by its name without .py: money.py is the module money.: a file whose functions other files can use. This runner has two files. Look at money.py in its tab, then run main.py:

import money

print(money.vat(200))
print(money.santim_to_birr(250))

def vat(price):
    return price * 15 // 100


def santim_to_birr(santim):
    return santim / 100

Ctrl or Cmd + Enter runs

importimportLoad a module so this file can use it: import money, then money.vat(200). money finds money.py (the module's name is the file's name without .py), runs it, and gives you the name money. You reach its functions with a dot, money.vat, just like random.randint in lesson 3.5. Change 15 to 10 in the money.py tab and run again: the first line becomes 20.

There are three ways to write an import:

import money
from money import vat
import money as m

print(money.vat(200))
print(vat(200))
print(m.vat(200))

def vat(price):
    return price * 15 // 100


def santim_to_birr(santim):
    return santim / 100

Ctrl or Cmd + Enter runs

import money keeps every name behind money., so you can always see where a function came from. from money import vat brings in just vat, to use without the dot. as gives a module a shorter name, as in import statistics as stats; use it for long names.

An import runs the file, once

Importing a module runs its whole file, top to bottom. This money.py has a print at the top, and main.py imports it twice. Predict:

ውጤቱን ገምቱ

Decide before you look. Guessing wrong is how this sticks.

import money
import money

print(money.vat(200))

Also in the folder with main.py:

money.py

print("Loading money")


def vat(price):
    return price * 15 // 100

Python prints

Loading money
30

The first import runs money.py, which prints. Python remembers modules it has already loaded, so the second import does nothing.

If you picked the first answer, you thought import only collects the functions; it runs the file, print and all. If you picked the last, you thought each import runs it again. Python runs a module the first time it's imported and remembers it for the rest of the run, so the second import money just gives you the same module. Run the program again and it starts fresh: Loading money prints again, once.

if name == "main":

Every module gets a name __name__. Here money.py prints its own __name__. First, main.py imports it. Predict:

ውጤቱን ገምቱ

Decide before you look. Guessing wrong is how this sticks.

import money

Also in the folder with main.py:

money.py

print("money.py sees", __name__)

Python prints

money.py sees money

An imported module's __name__ is its own module name: money. Only the file you run gets __main__.

Now run money.py itself, with python money.py. Predict again:

ውጤቱን ገምቱ

Decide before you look. Guessing wrong is how this sticks.

print("money.py sees", __name__)

Command

python money.py

Python prints

money.py sees __main__

The file Python starts from gets the name __main__, whatever the file is called.

The file you run gets __name__ set to "__main__"; a file that's imported gets its module name, "money". That's what lesson 5.8 promised: if __name__ == "__main__": means "only when this file is the one being run". Code under it runs when you run the file, and not when another file imports it. Here, money.py checks itself:

from money import vat

print(vat(300))

def vat(price):
    return price * 15 // 100


if __name__ == "__main__":
    print("Checking vat:", vat(200) == 30)

Ctrl or Cmd + Enter runs

The check doesn't print, because money.py was imported. In a terminal, python money.py would print Checking vat: True. That's why main() goes under that line: other files can import your functions without starting your whole program.

ጥያቄ

Inside money.py, what is __name__ when main.py does import money?

Names that clash

Python looks for a module in the folder of the file you ran first, before the standard library's files. (Only the few modules built into Python itself, like sys, are found before that.) So a file of yours named like a standard module takes its place:

የተለመደ ስህተት

This breaks

main.py

import random

print(random.randint(1, 6))

Also in the folder with main.py:

random.py

# Hana's dice practice
print("Rolling...")

Python says

AttributeError: module 'random' has no attribute 'randint' (consider renaming '/home/learner/random.py' since it has the same name as the standard library module named 'random' and prevents importing that standard library module)

The fix

# Rename random.py to dice_practice.py. Now this imports Python's random:
import random

print(random.randint(1, 6))

import random found Hana's random.py and ran it ("Rolling..." prints first), and her file has no randint. Read the last line: Python 3.14 even says to rename the file. Never name your files random.py, json.py, csv.py, or math.py.

One more kind of clash: from math import * brings in every name from math, and they replace yours without a word:

e = "Elias"
from math import *

print(e)

Ctrl or Cmd + Enter runs

math has a name e (a number), and it replaced Elias. With import math you'd write math.e, and your e would be safe. Avoid import *.

መልመጃ

Move the grade functions

grades.py already has the grade functions from lesson 5.8. main.py still has its own copies. Delete the copies from main.py and import grade_for and grade_points from grades instead. The program should print the same thing.

Output

Score (0-100): 85
Grade: A (4.0 points)

Your code

def grade_for(score):
    if score >= 85:
        return "A"
    elif score >= 70:
        return "B"
    elif score >= 50:
        return "C"
    else:
        return "F"


def grade_points(letter):
    points = {"A": 4.0, "B": 3.0, "C": 2.0, "F": 0.0}
    return points[letter]


def main():
    score = int(input("Score (0-100): "))
    grade = grade_for(score)
    print(f"Grade: {grade} ({grade_points(grade)} points)")


if __name__ == "__main__":
    main()

def grade_for(score):
    if score >= 85:
        return "A"
    elif score >= 70:
        return "B"
    elif score >= 50:
        return "C"
    else:
        return "F"


def grade_points(letter):
    points = {"A": 4.0, "B": 3.0, "C": 2.0, "F": 0.0}
    return points[letter]

Ctrl or Cmd + Enter runs

Input

One answer per line, given to input() in order.

መፍትሄውን አሳይ

This is one way to solve it, not the only one. If yours prints the same thing, it works.

from grades import grade_for, grade_points


def main():
    score = int(input("Score (0-100): "))
    grade = grade_for(score)
    print(f"Grade: {grade} ({grade_points(grade)} points)")


if __name__ == "__main__":
    main()

ዋና ዋና ነጥቦች

A module is a Python file other files can use; import money loads money.py.
import money (then money.vat) or from money import vat; avoid import *.
Importing runs the module's file once per program, however many times you import it.
__name__ is "__main__" in the file you run and the module's name when it's imported; code under if __name__ == "__main__": runs only when the file is run.
Python looks in your own folder first: never name a file random.py or json.py.