For Loops: Python

Introduction

• A for loop executes a block of code repeatedly
• For loops are used when the number of iterations is known in advance

Syntax of a for Loop

• Requires a variable placeholder and a sequence to iterate over
• The code block executes once for each item in the sequence

Using the range() Function

• The range() function generates a sequence of numbers
• range(start, stop, step) parameters include:
  • start refers to the starting number which is inclusive (default is 0)
  • stop refers to the ending number which is exclusive
  • step refers to the increment or decrement between numbers (default is 1)

Examples of for Loops

• Printing numbers from 1 to 5 involves using range(1,6) within the for loop and printing the iterator variable
• Looping through a list of strings accesses each string element
• Iterating through a string accesses each character

Using else with for Loops

• The else block executes after the loop finishes normally, which means it was not terminated by a break statement

Nested Loops

• Nested loops are loops inside other loops
• The inner loop completes all iterations for each iteration of the outer loop

Common Mistakes and Errors

• Indentation errors occur if the code inside the loop is not properly indented
• Off-by-one errors can occur with range boundaries
• Modifying the sequence while iterating should be avoided

Practice Problems

• To calculate the sum of numbers from 1 to 100:

  • Initialize a variable sum to 0
  • Iterate from 1 to 100 (inclusive) using a for loop
  • Add each number to sum
  • Print the final sum

• To calculate the factorial of a number:

  • Initialize a variable factorial to 1
  • Iterate from 1 to n (inclusive) using a for loop
  • Multiply each number with factorial
  • Print the final factorial

Conclusion

• The for loop is used for efficient programming with repetitive tasks
• Effectively using for loops is crucial for making code more efficient