Loops

for i in range(1, n + 1) runs the loop body once for each integer from 1 up to (but not including) n + 1 - so range(1, 6) gives 1, 2, 3, 4, 5. That + 1 trips everyone up at first: range's upper bound is exclusive, so you add one to actually include n.

A common pattern is a running total: start a variable at 0 before the loop, then add to it on every pass. By the time the loop ends, it holds the answer you built up one step at a time.

Your task: write total_up_to(n), returning the sum of every integer from 1 to n, inclusive, using a loop.

You'll practice:

Looping with for and range()
Accumulating a result in a variable

{
  "language": "python",
  "starterCode": "# Write total_up_to(n): sum of integers from 1 to n, inclusive.\ndef total_up_to(n):\n    pass",
  "solution": "def total_up_to(n):\n    total = 0\n    for i in range(1, n + 1):\n        total += i\n    return total",
  "hints": ["range(1, n + 1) gives 1, 2, ..., n - range's upper bound is exclusive.", "Start a total at 0 before the loop, then add each i to it.", "total_up_to(5) should be 15 (1+2+3+4+5)."],
  "tests": [
    { "name": "total_up_to(5) is 15", "code": "assert total_up_to(5) == 15, 'total_up_to(5) should be 15'" },
    { "name": "total_up_to(1) is 1", "code": "assert total_up_to(1) == 1, 'total_up_to(1) should be 1'" },
    { "name": "total_up_to(10) is 55", "code": "assert total_up_to(10) == 55, 'total_up_to(10) should be 55'" }
  ]
}