Mastering Python: Understanding Conditionals and Loops for Efficient Programming

CSE1300 Python (Continued)

Why Learn Conditionals and Loops? Core of Programming Logic: Conditionals and loops enable decision- making and repetition, two fundamental pillars of programming. Common Scenarios: Conditionals: Checking user input validity, responding to different cases. Loops: Automating tasks that repeat, iterating over data structures.

Conditionals Conditionals let your program choose different paths based on true/false conditions. if if-else if-elif-else Syntax: if condition: # code executed if condition is True else: # code executed if condition is False

The if Statement age = 18 if age >= 18: print("You are an adult!") Explanation: Checks if age >= 18. If that s true, it executes the print() statement inside the block. If it s false, the program skips that block. Indentation: Remember to indent the code (usually 4 spaces) inside the if block.

The if-else Statement age = 16 if age >= 18: print("You are an adult.") else: print("You are a minor.") Explanation: If the condition in if is met, the first block runs. Otherwise (else), the second block runs. Use Case: Perfect for an either/or scenario (adult vs. minor, success vs. failure, etc.).

The if-elif-else Statement grade = 85 if grade >= 90: print("A") elif grade >= 80: print("B") elif grade >= 70: print("C") else: print("F")

The if-elif-else Statement Multiple Checks: First if checks one condition; if not met, elif checks the next, etc. else covers any scenario not already handled by previous conditions. Avoid Long Chains: If conditions get too long, consider other structures (e.g., dictionaries, lookup tables).

Nested Conditionals Placing an if-else block inside another if-else block. x = 5 if x > 0: print("x is positive") if x % 2 == 0: print("and even") else: print("and odd") When to Use: Handling sub-conditions within a main condition. Caution: Too many nested levels can make code hard to read strive for clarity.

Best Practices for Conditionals 1. Keep Conditions Simple: Use straightforward comparisons. 2. Combine Logical Operators: (x > 5) and (x < 10), for example. 3. Limit Nesting: Deeply nested code is hard to maintain. 4. Descriptive Variables: Improves readability (e.g., is_logged_in instead of x). 5. Consistency: Always maintain proper indentation.

Loops A loop repeatedly executes a block of code while a condition holds or through a sequence of items. Two Main Loop Types in Python: 1. for loop 2. while loop Use Cases: Iterating over a range of numbers. Processing each item in a list. Repeating a piece of code until a condition is met.

The for Loop for item in sequence: # do something with item Sequence Examples: Lists, strings, ranges, or any iterable object. fruits = ["apple", "banana", "cherry"] for fruit in fruits: print(fruit) Prints each item in the fruits list.

Using range() with for for i in range(5): print(i) Outputs: 0, 1, 2, 3, 4 Why Use range(): Generates a sequence of integers. Variants: range(start, stop): start inclusive, stop exclusive. range(start, stop, step): control step size.

The while Loop while condition: # code block Execution: Continues to run as long as condition is True. count = 0 while count < 5: print("Count is:", count) count += 1 Key Point: Make sure the loop eventually ends (e.g., incrementing count).

Controlling Loops break and continue break: Exits the loop immediately. for i in range(10): if i == 5: break print(i) # stops printing at 4 continue: Skips the rest of the current iteration and moves to the next. for i in range(5): if i == 2: continue print(i) # skips printing 2

Controlling Loops break and continue Use Cases: break: Exit early if a certain condition is met. continue: Skip unwanted iterations.

Nested Loops A loop inside another loop. for i in range(3): for j in range(2): print(i, j) When to Use: Iterating over multi-dimensional structures (e.g., 2D lists). Performance Caution: Nested loops can grow the number of operations quickly use carefully for large datasets.

Best Practices for Loops Use Meaningful Names: Avoid for x in y:; choose descriptive variable names. Keep Loop Bodies Simple: Complex logic can be split into functions. Watch for Infinite Loops: Make sure while loops will eventually become false. Use enumerate() or zip(): Helps manage indices and multiple sequences more cleanly.

Built-In Libraries Definition: Python s standard library is a collection of modules that come pre-installed, offering a wide range of functionalities. Why Use Them: Save time: No need to reinvent the wheel for common tasks. High reliability: Maintained and tested by the Python core team

import math Use math or any other built-in module. Provides mathematical functions (trigonometry, exponentiation, etc.). import math print(math.sqrt(16)) # 4.0 print(math.pow(2, 3)) # 8.0 print(math.pi) # 3.141592653589793 Efficiently handle many common math operations without writing them yourself.

import random Generating random numbers, picking random items. import random print(random.random()) # between 0.0 and 1.0 print(random.randint(1, 10)) # integer between 1 and 10 fruits = ["apple", "banana", "cherry"] print(random.choice(fruits)) # picks a random fruit Usage: Great for small games, simulations, or testing.

import datetime Work with dates and times. from datetime import datetime now = datetime.now() print("Current date and time:", now) print("Year:", now.year) print("Month:", now.month) print("Day:", now.day) Use Cases: Logging events, scheduling tasks, or formatting time.

os and sys os: Interact with your operating system (create directories, list files, etc.). import os print(os.getcwd()) # current working directory sys: Access system-specific parameters and functions (like command- line arguments). import sys print(sys.argv) # list of command-line arguments

How to Import Modules Import Methods: 1. Basic: import math 2. Alias: import math as m 3. Selective: from math import sqrt, pi 4. Wildcard (not recommended): from math import * Why Different Methods? Alias shortens module names. Selective imports only bring in the parts you need. Wildcard can cause name conflicts.

Exploring the Python Standard Library Documentation Official Docs: docs.python.org Organization: Categorized by module name, e.g., math, random, datetime, etc. Why Use Docs?: See what functions and classes are available. Learn about parameters, return values, and examples.

Combining Conditionals, Loops, and Libraries Example: Guessing Game import random secret_number = random.randint(1, 10) attempts = 0 while True: guess = int(input("Guess a number between 1 and 10: ")) attempts += 1 if guess < secret_number: print("Too low! Try again.") elif guess > secret_number: print("Too high! Try again.") else: print(f"Correct! It took you {attempts} tries.") break

Explanation: 1. Uses random to generate a secret number. 2. Uses a while True loop to keep asking until guessed correctly. 3. Conditionals (if-elif-else) to guide the user s guesses. 4. break to exit the loop after the correct guess.

Debugging & Common Errors Infinite Loops: Forgetting to update a loop variable in a while loop. Indentation Issues: Misaligned blocks can cause unexpected logic flow or errors. NameError: Not importing a module but trying to use it. SyntaxError: Typos, missing colons, or parentheses in conditionals/loops. Fix Strategies: Print debugging statements, check variable updates, and carefully review indentation.