Introduction to Python Programming D2 chap 1

Python and Artificial Intelligence

• Created by Guido van Rossum in the late 1980s.
• Design focuses on code conciseness and readability.
• Used by companies like Instagram and Spotify.

Program Development

• Algorithms can be expressed in pseudocode but computers cannot understand it.
• Python programming language is used to communicate with computers.

From Pseudocode to Programming Languages

• Example: Calculating area of a square in Python:

  print("This is to find the area of a square!")
  length = input("Please enter a side length for a square: ")
  length = float(length)
  area = length * length
  print(area)

• Example: Calculating area of a square in C++:

  #include <iostream>
  using namespace std;
  int main() {
   float area, length;
   cout << "This is to find the area of a square!" << endl;
   cout << "Please enter a side length for a square: ";
   cin >> length;
   area = length * length;
   cout << area;
  }

Python Integrated Development Environment (IDE)

• IDE is an application with a code editor and programming-related functions.

Hello World!

• Simplest program to print "Hello World!".

Activity 4.1: Debugging "Hello World!"

Error 1

• Program Code:

  print "Hello World!"

• Error Message: SyntaxError: invalid syntax
• Cause of Error: Missing brackets.

Error 2

• Program Code:

  print(Hello World!)

• Error Message: SyntaxError: invalid syntax
• Cause of Error: Missing quotation marks around "Hello World!".

Error 3

• Program Code:

  print("Hello World!"

• Error Message: SyntaxError: unexpected EOF while parsing
• Cause of Error: Unclosed brackets; brackets must come in pairs. Quotation marks must also come in pairs.
• Case Sensitivity: Python is case-sensitive (e.g., "Print" is different from "print").
• print() function: Prints the text within the quotation marks; the content does not affect the program's execution.

Basic Programming Concepts

• Programming languages have keywords and similar concepts.

Variables

• Most programming languages require declaring the name and data type of a variable.
• The name becomes the identifier of the variable.

Common Data Types in Python

• Integer (int): Integers (positive and negative). Examples: 288, -101
• Float (float): Integers and decimals (positive and negative). Examples: 56.5, -30.0, -0.382
• Boolean (bool): True or False. 1 (True), 0 (False)
• String (str): Series of characters. Examples: "abc", "P%ssword123", "1", "k"

Assignment Operator

• Python uses "=" to assign data to a variable.
• Example:
  • Pseudocode: length <- 12
  • Python: length = 12
  • Output: <class ‘int’>
• Variables can switch between different data types in Python.

Built-in Functions for Data Type Conversion

• int(): Converts the input to an integer (rounds down if float).

  length = "12"
  print(length)  # Output: 12
  print(type(length))  # Output: <class ‘str’>
  length = int(length)
  print(length)  # Output: 12
  print(type(length))  # Output: <class ‘int’>

• float(): Converts the input to a float.

  length = 12
  print(length)  # Output: 12
  print(type(length))  # Output: <class ‘int’>
  length = float(length)
  print(length)  # Output: 12.0
  print(type(length))  # Output: <class ‘float’>

• str(): Converts the input to a string.

  length = 12.1
  print(length)  # Output: 12.1
  print(type(length))  # Output: <class ‘float’>
  length = str(length)
  print(length)  # Output: 12.1
  print(type(length))  # Output: <class ‘str’>

Activity 4.2: Debugging Data Types

Error 1

• Program Code:

  length = "12.1"
  length = int(length)

• Error Message: ValueError: invalid literal for int() with base 10: '12.1'
• Cause of Error: A decimal string cannot be directly converted to an integer. Convert to float first, then to int.

  length = "12.1"
  length = float(length)
  length = int(length)
  print(length)
  print(type(length))

Error 2

• Program Code:

  length = "ten"
  length = int(length)

• Error Message: ValueError: invalid literal for int() with base 10: 'ten'
• Cause of Error: Text in a string cannot be converted to numbers.

Constants

• Variables with fixed data, e.g., $\pi = 3.14159$.

Arithmetic Expressions

• Store the result of an arithmetic expression in a variable: variable = expression
• Arithmetic expressions are formed by data (numbers, variables, or constants) and arithmetic operators.

Python Arithmetic Operators

Activity 4.3: Debugging Variables

Error 1

• Code:

  “code” = 404
  print(“code”)

• Cause of error: The variable name does not include the double quotation marks.

Error 2

• Code:

SUBJECT = “ICT”
print(subject)

• Cause of error: Python is case-sensitive; SUBJECT and subject are two different variables.

Error 3

• Code:

B = A + 1
print(B)

• Cause of error: The undeclared variable A is used.

Error 4

• Code:

import = “5**”
print(import)

• Cause of error: “import” is a keyword, thus it cannot be used as the name of a variable.

Error 5

• Code:

fullname = “Peter Chan”
nickname = fullname – “Chan”

• Cause of error: Arithmetic operators are not applicable to the string data type.

Activity 4.4

Problem 1

A = 5
B = 9
C = A + B
print(C)

A = 3
B = A + 6
C = A * B
print(C - B)

Output: 14, 18

Problem 2

A = 3
B = 2
B = 2 * (A + B)
C = B ** 3
print(C - B)

A = 9
B = A * 5
print(A % B)
print(A // B)

Output: 990, 9, 0

Problem 3

a = 12
b = a + 10
c = b % 10
a = a**c
print(a//b)
print(type(a//b))

Output: 6,

Checkpoint 4.1

Problem 1.a

length = 20
width = 15
area = length * width
print(area)

Problem 1.b

length = 35
width = 10
perimeter = (length + width) * 2
print( perimeter )

Problem 1.c

PI = 3.14
r = 5
area = PI * r * r
print( area )

Problem 1.d

a = 13
b = 26
h = 5
area = ((a + b) * h) / 2
print(area)

Output and Input Statements:

• The print() function prints the content within the brackets (strings, variables, or expressions).

Examples:

• String:

  print(“Text”)
  

  Output: Text

• Variable:

  length = 10
  print(length)
  

  Output: 10

• Expression:
  python name = "Sam" print("Hi", name)
  Output: Hi Sam

Lab 4.2

name = "David"
mark = 89
print("Hi", name)
print("Your mark is", mark)

name = "David"
mark = 89
print("Hi", name, "your mark is", mark)

Output:

Hi David
Your mark is 89
Hi David your mark is 89

print("print something \"special\"")
name = "Sam"
print("Hi")
print(name)
print("Bye")
name = "Sam"
print("Hi", end="")
print(name, end="")
print("Bye")

Output:

print something "special"
Hi
Sam
Bye
HiSamBye

Input Statement:

• Programs require users to input the values of the variables using input().
• Input obtained by Python through the input() function will be stored as a string in a variable.

Example:

• Pseudocode: Input length
• Python: length = input()

Lab 4.3

length = input()
print(type(length))
length = int(input())
print(type(length))
width = float(input())
print(type(width))

Output:

<class ‘str’>
<class ‘int’>
<class ‘float’>

length = int(input())
width = float(input())
area = length * width
print(area)
print(type(area))
A = input()
B = input()
sum = A + B
print(sum)
print(type(sum))

Output:

300.0
<class ‘float’>
11
<class ‘str’>

Debugging Input:

Error 1

• Code:

  mark = int(input()
  print(mark)

• Cause of error: The brackets must come in pairs.

Error 2

• Code:

  mark1 = input()
  mark2 = input()
  avg_mark = (mark1 + mark2) / 2
  print(avg_mark)

• Cause of error: Arithmetic operators are not applicable to string data types. Need to convert mark1 and mark2 to float or int before calculate.

Checkpoint 4.2 Solutions:

Problem 1:

d = float(input("Please enter the diameter of the cylinder: "))
h = float(input("Please enter the height of the cylinder: "))
PI = 3.14
vol = PI * ((d/2)**2) * h
area = 2 * PI * (d/2) * h + 2 * PI * (d/2)**2
print("The volume of the cylinder is:", vol)
print("The surface area of the cylinder is:", area)

Problem 2:

name = input("Please enter your name: ")
test1 = float(input("Please enter the first test result: "))
test2 = float(input("Please enter the second test result: "))
exam = float(input("Please enter the exam result: "))
TEST1_WEIGHT = 0.2
TEST2_WEIGHT = 0.3
EXAM_WEIGHT = 0.5
overall = test1*TEST1_WEIGHT + test2*TEST2_WEIGHT + exam*EXAM_WEIGHT
print(name , end = "")
print(", your overall result of ICT is:", overall )

Problem 3:

print("This is a BMI Calculator!")
height = float(input("Please enter your height in meters: "))
weight = float(input("Please enter your weight in kg: "))
bmi = weight / (height**2)
print("Your BMI is", bmi)

Problem 4:

time = int(input("Input the number of seconds: "))
minutes = time // 60
seconds = time % 60
print("Your record is", minutes, "minute(s) and", seconds, "second(s).")

Functions:

• Python has many built-in functions, like print(), input(), type(), and int().

More built-in functions

Mathematical Functions

• To use functions not built-in, import a library (e.g., math).
• Some mathematical functions in the “math” library include:

Checkpoint 4.3

import math
a = float(input("One side of right triangle: "))
b = float(input("Another side of right triangle: "))
c = math.sqrt(a**2 + b**2)
print("The length of hypotenuse side is", c)

Random Functions

Problem 4.4

import random
DrawNumber = random.randint(1, 100)
print(DrawNumber)

Output: A single random integer between 1 and 100

Selection:

• The selection control structure allows the program to make decisions based on specified conditions.

Boolean Expressions:

Binary-way Selection:

"if…then" in Python:

• Pseudocode:

  if {condition} then
   {“then” body}

• Python:

  if {condition}:
   {“then” body}

• Example:

  mark = 70
  if mark >= 50:
   grade = "Pass"
   print(grade)

"if…then…else" in Python:

• Pseudocode:

  if {condition} then
   {“then” body}
  else
   {“else” body}

• Python:

  if {condition}:
   {“then” body}
  else:
   {“else” body}

• Example:

  mark = 70
  if mark >= 50:
   grade = "Pass"
  else:
   grade = "Fail"
  print(grade)

Debugging Conditional Statements:

Error 1:

• Code:

  mark = 70
  if mark >= 50
  print("Pass")

• Cause of error: Colon ":" should be added after the condition.

Error 2:

• Code:

  mark = 100
  if mark = 100:
  print("Congratulation!")

• Cause of error: Instead of assignment operator "=", relational operator "==" should be used in the condition.

Error 3:

• Code:

  mark = 70
  if mark >= 50:
  print("Pass")
  else:
  print("Fail")

• Cause of error: Indentation should be added before `print(