Python: Pythonの基本構文と変数

# ✅ Correct: consistent indentation within a block
if 3 > 1:
    print("3 is greater than 1")
    print("This line is also inside the if block")

# ❌ Error: inconsistent indentation
if 3 > 1:
    print("3 is greater than 1")
  print("Wrong indentation!")  # IndentationError

# Indentation in a for loop
for i in range(3):
    print(i)          # This line is inside the loop
    print("---")      # This line is also inside the loop
print("Done")         # This line is NOT inside the loop

# This is a single-line comment
print("Hello")  # Comment after code

# Multi-line comments use multiple # symbols
# This is line two
# This is line three

"""
This is a multi-line comment
Useful for writing function descriptions
Or temporarily blocking out large blocks of code
"""
print("The multi-line string above won't execute")

name = "Alice"    # str
age = 25          # int
height = 1.75     # float
is_student = True  # bool

# ✅ Variables: lowercase with underscores (snake_case)
user_name = "Alice"
total_price = 99.9
max_value = 100

# ✅ Constants: ALL_CAPS with underscores
PI = 3.14159
MAX_SIZE = 1024

# ❌ Not recommended
userName = "Alice"     # CamelCase (Java style)
UserName = "Alice"     # Looks like a class name

# Assign multiple values at once
a, b, c = 1, 2, 3
print(a, b, c)  # 1 2 3

# Swap two variables (other languages need a temporary variable)
x, y = 10, 20
x, y = y, x
print(x, y)  # 20 10

# Assign the same value to multiple variables
m = n = p = 0
print(m, n, p)  # 0 0 0

# Define variables of different types
name = "Alice"
age = 25
height = 1.68
is_student = True

# Print variable info
print(f"{name} is {age} years old, {height}m tall")
print(f"Student status: {is_student}")

# Swap two variables
a, b = 10, 20
print(f"Before: a={a}, b={b}")
a, b = b, a
print(f"After: a={a}, b={b}")

# Check types
print(f"name type: {type(name)}")
print(f"age type: {type(age)}")
print(f"height type: {type(height)}")

Alice is 25 years old, 1.68m tall
Student status: True
Before: a=10, b=20
After: a=20, b=10
name type: <class 'str'>
age type: <class 'int'>
height type: <class 'float'>

x = 42
y = 3.14
z = "Hello"
w = True

print(f"x = {x}, type = {type(x).__name__}")
print(f"y = {y}, type = {type(y).__name__}")
print(f"z = {z}, type = {type(z).__name__}")
print(f"w = {w}, type = {type(w).__name__}")

print(f"\nint(y) = {int(y)}")
print(f"float(x) = {float(x)}")
print(f"str(x) = {str(x)}")
print(f"bool(0) = {bool(0)}, bool(1) = {bool(1)}")

var = 100
print(f"\nvar = {var}, type = {type(var).__name__}")
var = "now a string"
print(f"var = {var}, type = {type(var).__name__}")

x = 42, type = int
y = 3.14, type = float
z = Hello, type = str
w = True, type = bool

int(y) = 3
float(x) = 42.0
str(x) = 42
bool(0) = False, bool(1) = True

var = 100, type = int
var = now a string, type = str

a, b, c = 10, 20, 30
print(f"a={a}, b={b}, c={c}")

x, y = 100, 200
print(f"Before swap: x={x}, y={y}")
x, y = y, x
print(f"After swap: x={x}, y={y}")

p = q = r = 0
print(f"p={p}, q={q}, r={r}")

colors = ["red", "green", "blue"]
first, second, third = colors
print(f"First: {first}, Second: {second}, Third: {third}")

a=10, b=20, c=30
Before swap: x=100, y=200
After swap: x=200, y=100
p=0, q=0, r=0
First: red, Second: green, Third: blue

print(type(10))       # <class 'int'>
print(type(3.14))     # <class 'float'>
print(type("Hello"))  # <class 'str'>
print(type(True))     # <class 'bool'>

# Variables can change type when reassigned (dynamic typing)
x = 10
print(type(x))  # <class 'int'>
x = "Hello"
print(type(x))  # <class 'str'>  ← type changed

# IndentationError: wrong indentation
print("Too much indentation")
  print("This line has an extra space")  # ❌

# NameError: variable not defined
print(z)  # ❌ z was never assigned

# SyntaxError: invalid syntax
print("Hello)  # ❌ quotes not closed