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Topic 2: Lists

Learning Outcomes:

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(f) Identify pre-defined list functions (len( ), min( ), max( ), � sum( ) and a method (append( ))

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Table of Contents

len() function

min() function

max() function

sum() function

In this lecture, we’ll mainly focus on these four (4) pre defined functions & one (1) method in list:

append() method

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4. The sum() function

What does it do?

  • The sum() function returns the sum of all the numerical values in a list.
  • Syntax of sum() function

sum(iterable,start)

The list of numbers to sum up.

(Optional) The value that is added to the sum of elements. The default is 0.

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Example 1: Sum of numbers in a list

numbers = [1, 2, 3, 4, 5]

total_sum = sum(numbers)

print("Sum of all elements in the list:", total_sum)

Output

Sum of all elements in the list: 15

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Example 2: Sum with a starting value.

numbers = [1, 2, 3, 4, 5]

total_sum = sum(numbers,100)

print("Sum of all elements in the list:", total_sum)

Output

Sum of all elements in the list: 115

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Example 3: sum() function on string list.

# List of strings

string_list = ["apple", "kiwi"]

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# Find the minimum string

sum_string = sum(string_list)

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print(sum_string)

Output

ERROR!

Traceback (most recent call last):

File "<main.py>", line 5, in <module>

TypeError: unsupported operand type(s) for +: 'int' and 'str'

=== Code Exited With Errors ===

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Difference between a function and a method

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​

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METHOD

FUNCTION

VS

how to call/invoke

NOTE:

Method is similar to function but attached to an object. Later, you will use this in lists etc.

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5. The append( ) method in Python

What does it do?

  • The append() method in Python is used to add an element to the end of a list.
  • It modifies the list in place and does not return a new list.
  • Syntax of append()

list.append(element)

The list you want to modify.

The item you want to add to the list.

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Example 1: Using append() with a List.

fruits = ["apple", "banana", "cherry"]

fruits.append("orange")

print(fruits)

Output

['apple', 'banana', 'cherry', 'orange']

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Example 2: Using append() with a Condition

numbers_list = [1, 2, 3, 4, 5]

new_number = 6

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if new_number not in numbers_list:

numbers_list.append(new_number)

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print(numbers_list)

Output

[1, 2, 3, 4, 5, 6]

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not in means that the number is not in the list

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Example 3: Using append() in a Function.

def add_item(my_list, item):

if item: # Ensures item is not empty or None

my_list.append(item)

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items = ["pen", "pencil"]

add_item(items, "eraser")

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print(items)

Output

['pen', 'pencil', 'eraser']

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Example 4: Appending Numbers from a Range

number_list = [] # Empty list

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for i in range(5):

number_list.append(i) # Add each number to the list

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print(number_list)

Output

[0, 1, 2, 3, 4]

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Example 5: Appending even numbers only

even_numbers = []

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for i in range(10):

if i % 2 == 0: # Check if number is even

even_numbers.append(i)

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print(even_numbers)

Output

[0, 2, 4, 6, 8]

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Example 6: Apply what you’ve learned so far. Count the number of positive number and find their sum

def sum_count_positiveNumbers(numbers_list):

positive_numbers = []

for num in numbers_list:

if num > 0:

positive_numbers.append(num)

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sum_of_positives = sum(positive_numbers)

count_of_positives = len(positive_numbers)

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print("Sum of positive numbers:", sum_of_positives)

print("Count of positive numbers:", count_of_positives)

# Example usage:

sample_list = [-1, 2, 3, -4, 5]

result = sum_count_positiveNumbers(sample_list )

Output

Sum of positive numbers: 10

Count of positive numbers: 3

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Write a Python program that allows the user to enter a series of numbers. The program should:

  • Add each number to a list using the append() method.
  • Calculate and display the total sum of all numbers using the sum() function.

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