git commit -m
"Code likho, Debug karo,
Clean rakho"

Week 7 basically "software development in practice" ke baare me hai. Ab tak humne design, requirements waghera dekha — is week hum dekhte hain ki actual me code likhte, share karte, debug karte aur measure kaise karte hain.

Flask kya hai?

Flask ek web application framework hai Python ka, aur ye ek micro-framework hai. "Micro" ka matlab — ye aap par zyada restrictions impose nahi karta: kaunsa database use karna hai, kaunsa web server — sab aapki choice. Lightweight aur flexible.

Problem kya solve kar rahe hain?

Developers badi teams me kaam karte hain. Toh issues aate hain:

Iska efficient solution = Version Control System (VCS).

Centralized vs Distributed VCS

Git — free & open source, Linus Torvalds ne 2005 me Linux kernel development ke liye banaya tha. GitHub = online Git repository hosting service (web GUI, access control, bug tracking, task management, CI, wikis).

Git ke 3 States — sabse important concept! 🔑

Staging area kyu hai? Socho aapne 10 files modify ki, but 3 sirf testing ke liye thi. Staging se aap sirf wahi files select kar sakte ho jo actually commit karni hain. Baaki chhod do.

Core Git Commands

$ git add lib file1.py
$ git commit -m "adding new files"

Branching

Branch = code ki ek independent line of development. Har feature / bug-fix ke liye alag branch banao, master ko stable rakho.

# nayi branch banao aur usme kaam karo
$ git checkout -b feature1
# changes karo...
$ git add changed_file.py
$ git commit -m "user story implemented"

Merging

Merge = ek ya zyada branches ke changes ko ek single branch me combine karna (taaki final software build ban sake).

$ git checkout master        # pehle master par aao
$ git merge feature1         # feature1 ke changes master me merge

Agar master aage badh chuka ho (koi aur commit aa gaya), toh Git three-way merge karta hai — no conflicts ho toh automatic, warna conflicts manually resolve karke merge karo.

Conflict kab hota hai? 😤

Jab do branches ne same file ki same lines ko alag-alag tarike se change kiya ho. Git confuse ho jata hai ki kaunsa version rakhe — developer ko decide karna padta hai.

Git Rebase

Scenario: Aap feature1 par kaam kar rahe the. Beech me priority issue aaya → issueP branch banai → fix karke (function fun1 add kiya) master me merge kar di. Ab feature1 me wapas aaye — but aapko fun1 chahiye jo feature1 me hai hi nahi (kyunki branch purane commit se bani thi)!

$ git checkout feature1
$ git rebase master          # feature1 ko master ke latest commit par le aao
# ab fun1() available hai — use karo, test karo
$ git checkout master
$ git merge feature1         # conflicts rebase me hi resolve ho chuke

Issue Tracking kya hai?

Jab developer / tester / user ko koi bug ya problem milti hai, wo ek issue report karta hai. Issue ko fix hone tak save aur track karna zaroori hai — warna bhool jayenge!

Pull Request (PR) + Code Review flow

Issue page se hi branch banao toh PR automatically issue se link ho jaata hai. Reviewer PR kholta hai, "Files changed" tab me changes dekhta hai, specific line numbers par comments add karta hai. Sab comments address hone ke baad reviewer Approve mark karta hai. Fir merge button se changes source branch me merge — aur linked issue apne aap close!

3 Key Terms — Error, Failure, Fault

Debugging = failure ka cause dhoondhna + code rectify karna taaki failure chala jaye. Steps: Reproduce the problem → Find the cause → Investigate & implement the fix → Test.

Debugging Techniques (tools/tarike) 🛠️

Debugging Strategies (approach/soch) 🧠

Python Debugger (pdb)

# tarika 1: command line se
$ python -m pdb myprogram.py

# tarika 2: code ke andar se
import pdb
pdb.set_trace()   # yahan execution pause hoga

Execution pause hota hai, aap line-by-line step kar sakte ho. Exit karne ke liye Ctrl+Z.

Software metrics = code ki complexity ko quantitatively measure karna. Complex code = samajhna mushkil = bugs ka zyada risk. Python me tool: Radon (pip install radon).

A. Cyclomatic Complexity (CC)

Formula ekdum simple: CC = number of decisions + 1

def lsearch(key, lst):
    for i in lst:        # decision 1
        if i == key:      # decision 2
            print("key found")
            return
    print("key not found")

Radon CC Ranks (A se F)

CC zyada ho toh solution: function ko chhote functions me split karo (refactoring). Radon command: radon cc -s file.py

B. Raw Metrics

Difference example: agar ek line ko \ (backslash) se do lines me todo, toh SLOC me 2 lines count hongi but LLOC me sirf 1. Command: radon raw file.py

C. Halstead Metrics

Code ki measurable properties aur unke relationships par based:

In 4 se calculate hote hain: vocabulary, program length, volume, difficulty, effort etc. Command: radon hal file.py

Code smells = code ki problematic/inelegant characteristics. Code kaam toh karta hai, but "kuch sahi nahi lag raha". Reference book: Clean Code by Robert Martin (63 code smells!).

Comments se related smells 💬

Functions se related smells 🔧

General smells 🌐

Pylint — static code analyzer

$ pip install pylint
$ pylint myfile.py

Pylint source code scan karke batata hai: naming convention issues (Python me snake_case chahiye), missing docstrings, unused variables, unreachable code. Message types: C = convention, W = warning. Doosre tools: flake8, Vulture. Zyaadatar IDEs (VS Code) me linters pre-installed hote hain.