Loops and Range()

The range() Function

The range() function generates a sequence of numbers, which is essential for loops in Python.

One Parameter: range(stop)

• Generates numbers from 0 up to (but not including) the stop value
• Example: range(5) produces: 0, 1, 2, 3, 4
• Why exclude the stop value? Makes it easier to count items since Python uses 0-based indexing
• If you want 5 numbers, use range(5) → gives you indices 0 to 4

Two Parameters: range(start, stop)

• Specify where to start and where to stop
• Start value is included, stop value is excluded
• Example: range(1, 5) produces: 1, 2, 3, 4
• To calculate how many numbers: stop - start (5 - 1 = 4 numbers)

Three Parameters: range(start, stop, step)

• Third parameter controls the increment (step size)
• Default step is 1
• Positive step: range(1, 5, 2) produces: 1, 3
  • Start at 1, increase by 2 each time, stop before 5
  • Number of items: (stop - start) / step = (5 - 1) / 2 = 2 numbers
• Negative step: range(1, -3, -1) produces: 1, 0, -1, -2
  • Creates a decreasing sequence
  • Start at 1, decrease by 1 each time, stop before -3
  • Number of items: (1 - (-3)) / 1 = 4 numbers

Key Point: range() is the essential tool for generating number sequences for loops.