Lesson 05 � Foundation

EK VALUE NAHI.
POORA COLLECTION.

Aapke paas sirf ek learner nahi, learners ki list hai. Ek task nahi, daily tasks hain. List ordered, mutable collection hai�yani values ki sequence jise aap later change kar sakte ho.

WHAT: list square brackets mein banti hai

skills = ["Python", "SQL", "Pandas"]

print(skills[0]) # Python
print(len(skills)) # 3

WHEN: collection ko update karna

append() end mein add karta hai; remove() matching value ko hatata hai; pop() index se item nikalta hai. Production code mein item exists karta hai ya nahi, woh check karna bhi zaruri hota hai.

tasks = ["Variables revise", "Strings practice"]
tasks.append("Lists exercise")
tasks[0] = "Variables project"

print(tasks)
# ['Variables project', 'Strings practice', 'Lists exercise']

WHERE: simple task tracker

List aapke first mini-project ka building block hai. Abhi loop complete nahi hua, fir bhi aap collection ko create/update aur display kar sakte ho.

Useful list operations

• items.sort() mutates the list; sorted(items) new sorted list deta hai.
• items[:2] slicing ke saath first two items deta hai.
• "Python" in skills membership check karta hai.
• Nested list tab use hoti hai jab collection ke andar collection ho; soon matrices aur tabular data se connect karoge.

Common mistakes

• Invalid index: list ke 3 items hain to items[3] error karega; last valid index 2 hai.
• remove() missing item ke saath error deta hai�external input par check karna seekho.
• sort() ka result variable mein assign mat karo; woh list ko in-place change karta hai aur None return karta hai.