CSE 160 Section 2

Loops and Range!

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TA1 & TA2

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CSE 160

CSE 160: Section 2

Logistics

• Homework: Practical (due Friday 4/10 @ 11:59pm)
• Submitting file on Gradescope - don’t change the file name!
• Wait for autograder!
• Section Assignment 2 (due Friday 4/10 @ 11:59pm)

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• Programming Practice 2 (due Tuesday 4/14 @ 11:59pm)
• Homework: DNA Analysis (due Friday 4/17 @ 11:59pm)
• Quest 1 in lecture (on Friday 4/17 @ 1:30pm)

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CSE 160: Section 2

Homework: Practical Tips

• Reminders:
• To run the file: %run FILE_NAME.py
• Check for formatting errors - flake8: !flake8 FILE_NAME.py
• Don’t change the filenames!
• Your output should exactly match the expected output.
• blanks should be replaced with your answers

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Diffchecker.com

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CSE 160: Section 2

DiffChecker Example

Diffchecker.com

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Problem 1 solution follows:

Root 1: ____

Root 2: ____

Problem 1 solution follows:

Root 1 : ____

Root 2 : ____

CSE 160: Section 2

DiffChecker Example

Diffchecker.com

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Problem 1 solution follows:

Root 1: ____

Root 2: ____

Problem 1 solution follows:

Root 1 : ____

Root 2 : ____

CSE 160: Section 2

Lecture Review: Range

CSE 160: Section 2

Range

• range(start, stop, step)
• range(start, stop)
• (inclusive, exclusive)
• Step is assumed to be 1
• range(stop)
• (exclusive)
• Step is assumed to be 1; Start is assumed to be 0

Example: range(0, 6, 2) loops through 0 → 2 → 4

Equivalent to: range(0, 5, 2)

Python Tutor

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CSE 160: Section 2

Lecture Review: Loops

CSE 160: Section 2

Loops

• Any variable name can be used in place of i (for good style, pick a variable name that fits the context)
• Indentation is a requirement to indicate loop body

for i in range(1, 4):

print(i)

PythonTutor

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CSE 160: Section 2

Loops

• Avoid redundancy
• More readable
• Avoid bugs
• Can easily make changes in code body,

or number of times loop is repeated

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CSE 160: Section 2

Nested Loops Overview

CSE 160: Section 2

Nested Loops

• A for loop within the body of another for loop

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Example:

for i in range(0, 3):

for j in range(0, 2):

print(i)

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CSE 160: Section 2

Nested Loops

• Nested loop structure
• Outer loop
• Inner loop

for i in range(0, 3):

for j in range(0, 2):

print(i)

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• Variable names i and j should be different for clarity

CSE 160: Section 2

Nested Loops

• Lets see what this outputs!

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Example:

for i in range(0, 3):

for j in range(0, 2):

print(i)

PythonTutor

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CSE 160: Section 2

Boolean Zen

• Minimize the use of if statements where possible!
• More readable
• Easier to debug

num = 0

if num == 2:

is_two = True

else:

is_two = False

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num = 0

is_two = num == 2

Without boolean zen:

With boolean zen:

CSE 160: Section 2

Section Handout Problems

CSE 160: Section 2

Ranges and Loops

2. Write a for loop that will print the result of multiplying 3 by the numbers 8 through 12.

The example solution is two lines long. Your output should read:

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24

27

30

33

36

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CSE 160: Section 2

Ranges and Loops

2. Possible solutions appear below:

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for value in range(8, 13):

print(3 * value)

for value in range(24, 37, 3):

print(value)

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*You’ll learn about lists soon!

for value in [8, 9, 10, 11, 12]:

print(3 * value)

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CSE 160: Section 2

Nested Loops

3. What is the output printed by the following program?

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sum = 0

for i in range(1, 4):

for j in range(1, 4):

sum = sum + i

print(sum)

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Answer: Python Tutor

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CSE 160: Section 2

Ranges and Loops

4. What is the output printed by the following program?

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for value in range(1, 6, 2):

print(value + value ** 2)

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CSE 160: Section 2

Ranges and Loops

4. What is the output printed by the following program?

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for value in range(1, 6, 2):

print(value + value ** 2)

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Output:

2

12

30

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CSE 160: Section 2

Additional Practice Problems

CSE 160: Section 2

Nested Loops

5. What is the output printed by the following program?

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for i in range(1, 4):

for j in range(1, 4):

print(i + j)

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Answer: Python Tutor

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CSE 160: Section 2

Ranges and Loops

6. What is the output printed by the following program?

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for value in range(1, 4):

print(value + value ** 2)

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CSE 160: Section 2

Section Code:

CSE 160: Section 2

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Looking ahead: Functions, Lists, and Nested Lists

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Be sure to remember the Section Code!

CSE 160: Section 2