Variables and Data Types - Deep Dive

Now that you understand the basics, let's explore variables and data types in much more depth.

Multiple Assignment

Python allows you to assign values to multiple variables in one line:

# Multiple assignment
x, y, z = 10, 20, 30
print(x, y, z)  # Output: 10 20 30

# Assign same value to multiple variables
a = b = c = 100
print(a, b, c)  # Output: 100 100 100

# Swap values (Python's elegant way!)
x, y = 5, 10
x, y = y, x
print(x, y)     # Output: 10 5

Advanced Numeric Types

Integers with Underscores

For readability with large numbers:

# Use underscores for readability
population = 7_800_000_000
print(population)  # Output: 7800000000

# Python integers can be arbitrarily large
huge = 123456789012345678901234567890
print(huge)

Floating-Point Numbers

price = 19.99
temperature = -5.5
pi = 3.14159

# Scientific notation
speed_of_light = 3.0e8  # 3.0 × 10^8
print(speed_of_light)   # Output: 300000000.0

# Very small numbers
planck = 6.626e-34
print(planck)

Complex Numbers

z = 3 + 4j
print(z)           # Output: (3+4j)
print(z.real)      # Output: 3.0
print(z.imag)      # Output: 4.0

Advanced String Operations

String Indexing

word = "Python"

# Positive indexing (starts at 0)
print(word[0])    # Output: P
print(word[-1])   # Output: n (last character)

String Slicing

word = "Python"

print(word[0:3])  # Output: Pyt
print(word[2:])   # Output: thon
print(word[:4])   # Output: Pyth
print(word[::2])  # Output: Pto (every 2nd character)
print(word[::-1]) # Output: nohtyP (reverse)

String Methods

text = "Hello, World!"

# Case conversion
print(text.upper())      # HELLO, WORLD!
print(text.lower())      # hello, world!
print(text.title())      # Hello, World!

# Searching
print(text.find("World")) # 7
print(text.count("l"))    # 3

# Replacing
print(text.replace("World", "Python"))  # Hello, Python!

Type Conversion in Depth

Converting Between Types

# String to Integer
age_str = "25"
age_int = int(age_str)
print(age_int + 5)  # 30

# String to Float
price_str = "19.99"
price_float = float(price_str)
print(price_float * 2)  # 39.98

# Number to String
score = 100
score_str = str(score)
print("Your score is " + score_str)

# Integer to Float
x = 5
y = float(x)
print(y)  # 5.0

# Float to Integer (truncates decimal)
pi = 3.14159
pi_int = int(pi)
print(pi_int)  # 3

Handling Conversion Errors

# This will cause an error
try:
    num = int("hello")  # ValueError
except ValueError:
    print("Cannot convert 'hello' to integer!")

# Check before converting
text = "123"
if text.isdigit():
    number = int(text)
    print(number)

The None Type

Represents the absence of a value:

result = None
print(result)  # Output: None
print(type(result))  # <class 'NoneType'>

# Checking for None
if result is None:
    print("No value assigned")

Boolean Operations

# Boolean values
is_raining = True
is_sunny = False

# Boolean from comparisons
age = 18
is_adult = age >= 18
print(is_adult)   # Output: True

# Boolean operations
print(True and False)   # False
print(True or False)    # True
print(not True)         # False

Truthy and Falsy Values

# Falsy values (evaluate to False)
print(bool(0))           # False
print(bool(""))          # False (empty string)
print(bool([]))          # False (empty list)
print(bool(None))        # False

# Truthy values (evaluate to True)
print(bool(1))           # True
print(bool("Hello"))     # True
print(bool([1, 2]))      # True

Best Practices

Variable Naming

# Good - descriptive names
student_count = 30
max_temperature = 75
user_email = "alice@example.com"

# Bad - unclear
x = 30
temp = 75
ue = "alice@example.com"

Constants

# Use UPPERCASE for constants
PI = 3.14159
MAX_ATTEMPTS = 3
DEFAULT_COLOR = "blue"

Practice Exercises

1. Create variables with different data types and swap their values
2. Convert between different numeric types and observe the results
3. Use string slicing to extract parts of a sentence
4. Check if values are truthy or falsy
5. Practice type conversion with error handling

Next Lesson: Operators and Expressions