Modules — import, from…import, as aliasing

1.3.1 · Coding › Python Intermediate

Modules KYUN exist karte hain?

`import` par ACTUALLY kya hota hai

Figure — Modules — import, from…import, as aliasing

KAISE import karein — char forms

Form 1: `import module`

import math
print(math.pi)        # 3.14159...
print(math.sqrt(16))  # 4.0

Form 2: `from module import name`

from math import pi, sqrt
print(pi)        # prefix ki zaroorat nahi
print(sqrt(16))  # 4.0

Form 3: `import module as alias`

import numpy as np
np.array([1, 2, 3])

Form 4: `from module import name as alias`

from datetime import datetime as dt
now = dt.now()

Ye clash avoid karne ke liye use hota hai (yahan module datetime aur class datetime ka naam ek hi hai).

Python KAHAN dekhta hai? (`sys.path`)

Worked examples

Worked example Example 1 — clean prefixed import

import math
area = math.pi * math.pow(3, 2)   # circle radius 3
print(round(area, 2))             # 28.27

math.pi kyun? Kyunki import math ne sirf naam math bind kiya; pi uske andar rehta hai. round kyun? math.pi ek lamba float hai; hum display ke liye trim karte hain — round built-in hai, koi import ki zaroorat nahi.

Worked example Example 2 — saaf padhne ke liye selective import

from statistics import mean, median
data = [3, 1, 4, 1, 5, 9, 2]
print(mean(data))    # 3.571...
print(median(data))  # 3

from … import kyun? Math English jaisi padhi jaati hai (mean(data)), statistics. ka koi shor nahi. Dono naam list kyun? Explicit imports clearly document karte hain ki ye file kya depend karti hai.

Worked example Example 3 — clash avoid karne ke liye aliasing

from datetime import datetime as dt, timedelta
tomorrow = dt.now() + timedelta(days=1)
print(tomorrow.date())

as dt kyun? Class datetime module datetime ke andar rehti hai; aliasing confusion rokti hai aur calls chhoti karta hai. timedelta un-aliased kyun? Uska naam pehle se clear aur unique hai — rename karne ki koi wajah nahi.

Worked example Example 4 — prove karna ki "import sirf ek baar run hota hai"

# mymod.py
print("mymod is being executed!")
x = 42

# main.py
import mymod   # prints "mymod is being executed!"
import mymod   # KUCH nahi print hota — sys.modules mein cached hai
print(mymod.x) # 42

Doosri baar kuch kyun nahi? Python pehle sys.modules check karta hai; mymod wahan pehle se milne par, wo re-execution skip kar deta hai. Ye kyun matter karta hai: module-level code (DB connections, prints) exactly ek baar run hota hai — predictable aur fast.

Recall Feynman: ek 12-saal ke bachche ko samjhao (click karke kholein)

Socho tumhare toy box mein ek calculator toy hai (math). Tum keh sakte ho "toy box, apna calculator do" (import math, phir math.sqrt) — tum apne har toy se pehle "toy box ka" kehte ho taaki apne toys ke saath mix na ho. Ya tum calculator bahar nikalke apni desk pe rakh sakte ho (from math import sqrt) aur seedha pakad sakte ho — lekin dhyan raho, agar tumhare desk pe pehle se koi cheez "calculator" naam ki thi, to nayi cheez usse dhak degi! Aur as bas toy pe ek nickname sticker lagana hai taaki tum use kuch chhota bol sako.

Flashcards

Python module kya hota hai?

Ek single .py file jisme reusable code (functions, classes, variables) hota hai.

Module aur package mein kya fark hai?

Module ek .py file hoti hai; package ek folder hota hai modules ka jisme __init__.py hoti hai.

import math ke baad sqrt kaise call karein?

math.sqrt(...) — tumhe math. prefix use karna hoga.

from math import sqrt ke baad sqrt kaise call karein?

Bas sqrt(...) — naam tumhare namespace mein copy ho gaya, koi prefix nahi.

Import mein as kya karta hai?

Imported module/naam ko ek alias (nickname) deta hai — wahi object, chhota label.

from module import * kyun discourage kiya jaata hai?

Ye sab public names tumhare namespace mein dump kar deta hai, origins chhupa deta hai aur tumhare apne variables ko silently overwrite kar sakta hai.

Repeated imports par Python ek module ka top-level code kitni baar execute karta hai?

Sirf ek baar — baad ke imports sys.modules cache se serve hote hain.

Python import ke liye module kahan dhundta hai?

sys.path mein listed folders mein (script dir, PYTHONPATH, phir standard/installed libs), pehla match jeet jaata hai.

Apni file ka naam random.py rakhne se import random kyun toot jaata hai?

Tumhari local file sys.path par pehle milti hai aur real standard-library module ko shadow kar deti hai.

Modules ke context mein namespace kya hota hai?

Namen ka container; import module module ke naamon ko uske prefix ke peeche rakhta hai taaki wo tumhare se clash na karein.

Connections

Python Functions — modules zyaadatar reusable functions bundle karte hain.
Namespaces and Scope — import fundamentally namespaces mein naam bind karne ke baare mein hai.
sys and os modules — sys.path aur sys.modules import resolution control karte hain.
Packages and __init__.py — ek file se kai files tak scale karna.
Virtual Environments and pip — third-party modules sys.path par kaise aate hain.
DRY Principle — wo design idea jo modules ko motivate karta hai.