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Programming Essentials in Python Lecture 2 ​

Python Number Types: Integers, Floats, and Complex Numbers ​

Integers ​

  • Integers are whole numbers (zero, positive, or negative) without any fractional part. They are of unlimited precision in Python.
  • All integer literals or variables belong to the int class.

You can use type() to verify the class of an integer:

python
x = 10
print(type(x))  # Output: <class 'int'>

Integer Literals ​

  • Integers can be represented in binary, octal, and hexadecimal forms:
    • Binary: Prefix 0b
    • Octal: Prefix 0o
    • Hexadecimal: Prefix 0x
python
print(0b1010)  # Binary, Output: 10
print(0o12)    # Octal, Output: 10
print(0xa)     # Hexadecimal, Output: 10
  • Leading Zeros: Non-zero integers cannot have leading zeros (e.g., 0123 is invalid).
  • Underscores: Use _ as a separator in large numbers for readability.
python
x = 1_234_567
print(x)  # Output: 1234567
  • Integer Conversion: Convert strings or floats to integers using int().
python
print(int("100"))      # Output: 100
print(int("5.5"))      # Truncates to Output: 5
print(int("100", 2))   # Binary '100' to int, Output: 4

Floating-Point Numbers (Floats) ​

  • Floats represent real numbers with fractional parts, using a decimal or scientific notation (E or e).
python
z = 1.5
print(z)               # Output: 1.5
print(type(z))         # Output: <class 'float'>
print(3e3)             # Output: 3000.0
  • Scientific Notation: Floats can represent very large or small numbers using scientific notation (e.g., 1e-5 represents 1×10−5).
python
x = 6.022e23
print("x =", x)        # Output: 6.022e+23
  • Underscore Separator: Floats can include underscores for readability.
python
f = 123_42.222_013
print(f)               # Output: 12342.222013
  • Convert to Float: Convert strings or integers to floats using float().
python
print(float("5.5"))    # Output: 5.5
print(float("1e3"))    # Output: 1000.0
print(float("-inf"))   # Output: -inf

Complex Numbers ​

  • Complex Numbers in Python have both real and imaginary parts, written as a + bj, where j represents the imaginary unit.
python
# Define complex numbers
a = 8 + 3j
b = 2 + 1j

print(a)               # Output: (8+3j)
print(type(b))         # Output: <class 'complex'>

# Basic operations
addition = a + b       # (10+4j)
subtraction = b - a    # (-6-2j)
multiplication = a * b # (13+14j)
division = a / b       # (3.8-0.4j)

Strings ​

  • Strings are defined with either single or double quotes. Escape special characters with a backslash \.
python
print("Did you know that 'word' is a word?")
print('Did you know that "word" is a word?')
print('Did you know that \'word\' is a word?')
print("Did you know that \"word\" is a word?")

Converting Strings to Numbers and Vice Versa ​

  • Convert strings to integers or floats with int() and float() respectively. Convert numbers to strings with str().
python
print(int("54"))       # Output: 54
print(str(81))         # Output: '81'

Control Codes in Strings ​

  • Special characters within strings use control codes:
    • \n: Newline
    • \t: Tab
    • \b: Backspace
    • \a: Alert (beep)
python
print("P\nQ\nR")       # Outputs on new lines
print("S\tU\tV")       # Outputs with tabs
print("WX\bYZ")        # Removes the character before 'Y'
print("\a")            # Starts an alert sound 'Beep'

User Input ​

  • Getting User Input: Use input() to get input from users, and int() or float() to convert it to the desired type.
  • Example: A simple calculator that adds two integers.
python
# Get two integer inputs and print their sum
num1 = int(input("Please enter an integer value: "))
num2 = int(input("Please enter another integer value: "))
print(num1, "+", num2, "=", num1 + num2)

Variable Naming Rules and Identifiers ​

  • Identifiers: Variable names (identifiers) must start with a letter or underscore, followed by letters, numbers, or underscores.
  • Reserved Words: Keywords (e.g., if, while, True) cannot be used as identifiers.