Variables and Data Types

String methods — built-in actions you can call on any string

message = "  Hello, World!  "

print(message.upper())      # "  HELLO, WORLD!  "  — all caps
print(message.lower())      # "  hello, world!  "  — all lowercase
print(message.strip())      # "Hello, World!"       — removes surrounding spaces
print(message.replace("World", "Python"))  # "  Hello, Python!  "

name = "alice"
print(name.capitalize())    # "Alice"  — first letter uppercase only
print(name.title())         # "Alice"  — title case (good for names)

Methods are called using a dot . after the variable name. Python has dozens of string methods — these are the most useful ones to start with.

Multiline strings — triple quotes

Need to store text that spans multiple lines? Use three quotes:

poem = """
Roses are red,
Violets are blue,
Python is awesome,
And so are you!
"""
print(poem)

Triple quotes preserve all line breaks and indentation exactly as written. Very useful for long messages, templates, or documentation.

Escape characters — special characters inside strings

print("Line 1\nLine 2")      # \n = new line
print("Col1\tCol2")          # \t = tab (indent)
print("He said \"Hello\"")  # \" = literal quote inside string

The backslash \ tells Python "this next character is special". The most common are \n (new line) and \t (tab).

Checking string length

password = "securePass123"
print(len(password))          # 13

# Useful for validation:
if len(password) >= 8:
    print("Password is long enough")  # You'll learn 'if' in Lesson 3!

len() works on any string. It counts every character — letters, numbers, spaces, and symbols.

Assign multiple variables in one line

# Instead of three separate lines:
x = 5
y = 10
z = 15

# You can write one line:
x, y, z = 5, 10, 15

# Check they worked:
print(x, y, z)    # 5 10 15

The number of variables on the left must exactly match the number of values on the right — otherwise Python raises a ValueError.

Assign the same value to multiple variables

# Set multiple counters to zero at once:
lives = score = level = 0
print(lives, score, level)    # 0 0 0

# Useful for initialising several related variables:
red = green = blue = 255

Swapping two variables — Python's elegant trick

In most languages, swapping two variables requires a temporary "placeholder" variable. Python doesn't:

a = 5
b = 10
temp = a   # save a
a = b      # overwrite a
b = temp   # restore old a

a = 5
b = 10
a, b = b, a   # swap!
print(a, b)   # 10 5

This works because Python evaluates the entire right side first, then assigns. It's one of the small reasons developers enjoy writing Python.

What works and what doesn't

# ✅ These work:
int("42")        # → 42    (text digits → integer)
float("3.14")    # → 3.14  (text decimal → float)
str(100)         # → "100" (number → text)
bool(0)          # → False
bool("hello")    # → True

# ❌ These FAIL with a ValueError:
int("3.14")      # ERROR — can't convert decimal string to int directly
int("hello")     # ERROR — not a number at all
float("abc")     # ERROR

The two-step conversion trick

To convert "3.14" to an integer, you need to go through float first:

text = "3.14"

# ❌ This fails:
result = int(text)          # ValueError!

# ✅ This works — convert to float first, then to int:
result = int(float(text))   # → 3  (decimal is dropped, not rounded)

Notice: int() truncates (drops the decimal) rather than rounding. int(3.9) gives 3, not 4.

Full conversion reference