Modules: import, from, search path

You will be able to

• ✓ Treat a module as a .py file of names that import can load
• ✓ Keep import quiet — no receipt at load time
• ✓ Know the search path is why a USB script fails on the lab PC (reload is interactive only)

import loads a file of names once

fees.py holds late_fee and maybe CONFIG. import fees loads that file and binds the module name. from fees import late_fee copies the function into your file’s names. Either way, running the import must not print a hostel receipt. If it does, every test and every dashboard that imports fees prints a receipt. The door stays in the next lesson; the habit starts here: functions at the top, silence at load.

Python searches a list of folders (sys.path on a laptop) for fees.py. “It works on my USB” fails when the lab PC’s path does not include that stick. Put the project in one folder, run from that folder, or install the package. Do not copy fees.py into site-packages by hand.

# fees.py
def late_fee(days):
    if days <= 0:
        return 0
    return 25

# app.py
import fees
from fees import late_fee
print(late_fee(4))
# importlib.reload(fees)  # REPL only, not a nightly job

from and reload are easy to misuse

from fees import late_fee is convenient. from fees import * is how names collide — avoid it until you meet __all__. importlib.reload is an interactive habit after you edited a file in a long REPL session. Production jobs start a new process; they do not reload. This sandbox cannot import, so you practise two functions in one file-shaped program: the “module” stays quiet until the “app” prints.

Words that matter

Module

A Python file whose names can be imported.

import

Load the file once; bind the module (or copy names with from).

Search path

Folders Python walks to find fees.py — why USB ≠ lab PC.

reload

Interactive re-load after an edit — not a production pattern.

Common mistakes

On a full Python install — your own module

Save late_fee in fees.py and import it from app.py. Import must stay silent. Search path is the project folder.

No pip — files you wrote.

Quiet import, one public function.

# fees.py
def late_fee(days):
    if days <= 0:
        return 0
    return 25

# app.py
from fees import late_fee

print(late_fee(4))

Example program — Two callers, one module-shaped function

Kiosk and batch both call late_fee. Neither copies the 25.

Your turn — Silent rule, loud caller

Define gst(amount) as amount * 118 / 100. Print only gst(100) so 118 appears.

Self-assessment

Check your understanding before you mark the lesson complete.