Lesson 11: For Loops & Ranges#

Overview & Introduction#

This lesson introduces the ‘for loop’, a programming structure that repeats a block of code for each item in a known sequence or range. In the previous lesson, students used ‘while loops’ to repeat actions as long as a condition remained true, which is ideal when the stopping point depends on changing program state. The ‘for loop’, by contrast, provides a simpler and more predictable approach when the number of repetitions, or the data to iterate over, is known ahead of time. By exploring how Python’s range() function generates controlled sequences, students will learn when a ‘for loop’ is the more appropriate choice and how it builds on their earlier understanding of condition-driven repetition.

Learning Objectives#

By the end of this 50-minute class, students will be able to identify and explain the syntax and structure of a for loop, use the range() function to control repetition, iterate over lists, strings, and tuples to process each element, and compare for loops and while loops to determine which construct is most appropriate for a given problem. Each objective is directly assessed through in-class coding activities and the exit ticket.

Prerequisites#

Students should already understand variables, lists, and basic while loops. Each student needs a computer with Python installed (Thonny, IDLE, or Replit). The instructor should have a projector or shared screen and handouts with short practice prompts. All tasks can be done in person or remotely.

Lesson Outline#

1. Warm-Up (5 minutes)#

Ask students:

Start with a real-world prompt such as, “How could a computer print every student’s name in the class automatically?” Connect this to the prior lesson’s while loop and emphasize that for loops remove the need for manual counters. State that this lesson will show how to repeat tasks for known amounts of data

2. For Loop Syntax (10 minutes)#

Concept Explanation:

A for loop lets you repeat a block of code for every item in a sequence or for a specific number of iterations.

Syntax:

for *variable* in *sequence*:

Example:

for i in [1, 2, 3]:
    print("Value of i:", i)

Discussion:

Explain that the loop variable takes each value from the sequence and that indentation defines the block. Briefly show a diagram of the iteration cycle and demonstrate an indentation error to reinforce syntax rules. Keep discussion short but interactive—ask what happens if indentation is removed.

3. The Range Function (15 minutes)#

Concept Explanation:

range() generates a sequence of numbers — often used with for loops when the number of repetitions is known.

Examples:

for i in range(5):
    print(i)    # 0, 1, 2, 3, 4

for i in range(2, 6):
    print(i)    # 2, 3, 4, 5

for i in range(10, 0, -2):
    print(i)    # 10, 8, 6, 4, 2

Activity:

Ask students to predict outputs before execution. Clarify that range() returns a range object, not a list, by printing both range(5) and list(range(5)). Explain that Python’s _range() follows a half-open interval convention, also known as an open-ended or open-closed range, which means it includes the starting value but excludes the ending value. For example, range(2, 6) produces [2, 3, 4, 5] but does not include 6 . Conclude with a quick edge-case demo, range(5, 5), to illustrate empty ranges.

4. Iterating Over Sequences (20 minutes)#

Concept Explanation:

for loops aren’t just for numbers — they can iterate over any iterable sequence such as lists, strings, or tuples.

Examples:

(a) Iterating Over a List

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

(b) Iterating Over a String

for letter in "hello":
    print(letter)

(c) Iterating Over a Tuple

coordinates = (3, 5, 7)
for value in coordinates:
    print(value)

(d) Using ``range(len(sequence))``

fruits = ["apple", "banana", "cherry"]
for i in range(len(fruits)):
    print(i, fruits[i])

Assign two short collaborative coding challenges:

Number Squares – Display each number 1–5 and its square.
Counting Vowels – Ask the user for a word and count its vowels.

Students should work in pairs, test their code, and explain results to one another. If time allows, add a quick bonus: “Sum the numbers in [2, 4, 6, 8, 10].”

Exercise 1:

Print the square of every number from 1 to 5.

for i in range(1, 6):
    print(i, "squared is", i**2)

Exercise 2:

Count how many vowels are in a word.

word = input("Enter a word: ")
count = 0
for letter in word:
    if letter in "aeiou":
        count += 1
print("Vowels:", count)

Exercise 3:

Sum numbers in a list.

numbers = [2, 4, 6, 8, 10]
total = 0
for n in numbers:
    total += n
print("Sum:", total)

6. Reflection and Assessment (5 minutes)#

Lead a short discussion: How does a for loop differ from a while loop? Ask one or two students to rewrite a for loop as a while loop aloud. Finish with the exit ticket:

“Write a for loop that prints every other even number from 0 to 10.” Collect responses or review verbally to verify understanding of range(start, stop, step).

Quick Exit Question:

“Write a for loop that prints all even numbers from 0 to 10.”

Optional Homework#

For reinforcement, assign one small program: Print each letter in a word along with its position using range().

Optional challenge: use a nested loop to print coordinate pairs ((0 :raw-latex:`\leq `x, y :raw-latex:`leq 2`)).

Formative assessment occurs through predictions, debugging, and peer explanations. Summative evaluation is based on the guided practice and exit question. Students who meet all objectives will demonstrate correct syntax, logical use of range(), and the ability to adapt the loop to different sequence types.

This lesson condensed the fundamentals of the for loop, its syntax, use of range(), and application to lists, strings, and tuples. Students should now understand when to apply for loops for known repetitions. Next class, they will extend this knowledge to practice combining loops with conditionals.

📝 Luce, Jason Please see my overall review and detailed section-by-section suggestions/comments.

High-level review:

Category	Strengths	Areas for Improvement
Organization/Alignment	Clear flow from warmup, to explanation, to examples, to practice, to reflection.	Could add more explicit connections to Lesson 10 (While Loops).
Learning Objectives	Concise and relevant to basic Python concepts	N/A
Concept Accuracy	Explanations and syntax are correct. Examples of range and sequence iteration are accurate and varied.	See specific suggestions to expand examples.
Pedagogy	Good flow, promotes reflection/discussion/interaction. Good mix of prediction/execution. Clear formative vs summative evaluation.	Pair programming and real-world examples could be expanded.
Materials	Clear materials and is adaptable.	Could add a worksheet or provide code snippets for students to come further, reducing typing time.

Per-section suggestions/comments:#

Section/Title	Suggested Change	Details
Materials Needed	Edit	Rephrase “computer with Python …” to “computer with Python installed”.
Warm-up	Add	Add some follow-up questions to deepen the real-world connection. E.g., “How would a computer do this for a list of 1000 names?”
For Loop Syntax	Add	Include a simple diagram or visual representation of the loop iteration process.
For Loop Syntax	Add	After example, explicitly ask “what happens if we remove the indentation?”
The Range Function	Add	Clarify that `range()` returns a range object, not a list, and demonstrate: `r = range(5)` then `print(r)` vs `print(list(r))`.
The Range Function	Add	Include an example showing an empty range, e.g., `range(5, 5)`.
Iterating Over Sequences	Add	Might briefly introduce `enumerate()` as an advanced option. For example: `for index, item in enumerate(fruits): print(index, item)`.
Iterating Over Sequences	Edit	Visually separate the `range(len(...))` example to better highlight the relative complexity compared to directly iterating over a string or list.
Guided Practice / Mini-Projects	Edit/Add	Instead of providing full code, jump straight to the prompt. Let students write the input/code. Using partially finished templates could help. Students should reason through the code more actively.

Lesson 11: For Loops & Ranges

Contents

Lesson 11: For Loops & Ranges#

Overview & Introduction#

Learning Objectives#

Prerequisites#

Lesson Outline#

1. Warm-Up (5 minutes)#

2. For Loop Syntax (10 minutes)#

3. The Range Function (15 minutes)#

4. Iterating Over Sequences (20 minutes)#

6. Reflection and Assessment (5 minutes)#

Optional Homework#

Per-section suggestions/comments:#