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Syntax, Statements, and Output

What You'll Learn​

How Python reads code line by line, why indentation matters, and how to use print() to display results.

Python Is Indentation-Sensitive​

Most languages use {} braces to group code. Python uses indentation (spaces/tabs) instead.

This is correct:

if True:
    print("Inside the if block")
print("Outside the if block")

This will cause an error:

if True:
print("Missing indentation!")  # IndentationError

Rule: Use 4 spaces per indentation level. Never mix spaces and tabs.

Statements​

A statement is one instruction for Python to execute. Each line is usually one statement:

name = "Alice"       # statement 1: assign a value
age = 30             # statement 2: assign another value
print(name, age)     # statement 3: display them

You can split a long statement across lines using \:

total = 100 + 200 + \
        300 + 400
print(total)  # 1000

The print() Function​

print() displays text or values in the terminal. It's the most important tool for learning Python.

print("Hello, World!")
print(42)
print(3.14)
city = "Tokyo"
print(city)
print("Name:", "Alice", "Age:", 30)
# Output: Name: Alice Age: 30

Custom separator​

print("2024", "01", "15", sep="-")
# Output: 2024-01-15

Custom ending (default is newline)​

print("Loading", end="...")
print("Done")
# Output: Loading...Done
print("Line 1")
print("Line 2")
print("Line 3")
print()

F-Strings (Formatted Output)​

The cleanest way to embed variables in text:

name = "Bob"
score = 95

print(f"Player {name} scored {score} points!")
# Output: Player Bob scored 95 points!

You can put any expression inside {}:

width = 10
height = 5
print(f"Area: {width * height}")
# Output: Area: 50

Indentation in Practice​

temperature = 35

if temperature > 30:
    print("It's hot!")
    print("Drink water.")
else:
    print("It's comfortable.")

print("End of weather check.")

Output:

It's hot!
Drink water.
End of weather check.

Common Mistakes​

MistakeExampleFix
Missing colon after if/forif x > 0Add : → if x > 0:
Wrong indentation2 spaces instead of 4Stick to 4 spaces
Missing quotesprint(hello)Write print("hello")
Unclosed parenthesisprint("hi"Add closing )

Quick Reference​

# Basic print
print("text")
print(42)
print(variable)

# Multiple values
print("a", "b", "c")          # a b c
print("a", "b", sep="-")      # a-b

# No newline at end
print("hello", end=" ")

# F-string
name = "Alice"
print(f"Hi {name}")            # Hi Alice

# Blank line
print()

Practice Exercises​

  1. Indent it: Write an if block that prints "Positive!" when a number is greater than 0.
  2. Format: Use an f-string to print your name and age on one line.
  3. Separator: Print the date 2024/06/15 using print("2024", "06", "15", sep="/").
  4. No newline: Print "Loading..." without a newline, then "Done!" on the same line.

What's Next​

→ Lesson 3: Variables, Names, and Casting