Python Tutorial — Learn Python Step by Step

# int() — convert to integer
a = int("42")         # str to int: 42
b = int(3.99)         # float to int: 3 (truncates, does NOT round)
c = int(True)         # bool to int: 1
d = int("0xFF", 16)   # hex string to int: 255

# float() — convert to float
e = float("3.14")     # str to float: 3.14
f = float(42)         # int to float: 42.0
g = float("inf")      # infinity

# str() — convert to string
h = str(100)          # "100"
i = str(3.14)         # "3.14"
j = str(True)         # "True"
k = str([1, 2, 3])   # "[1, 2, 3]"

# bool() — convert to boolean
print(bool(0))        # False
print(bool(1))        # True
print(bool(""))       # False (empty string)
print(bool("hello"))  # True (non-empty string)
print(bool([]))       # False (empty list)
print(bool([1]))      # True (non-empty list)

# Python automatically converts int to float in mixed arithmetic
result = 5 + 3.0     # int + float = float (8.0)
print(type(result))  # <class 'float'>

# bool to int in arithmetic
total = True + True + False  # 1 + 1 + 0 = 2

# String concatenation requires explicit conversion
age = 25
# print("Age: " + age)      # TypeError!
print("Age: " + str(age))   # "Age: 25" (explicit)
print(f"Age: {age}")         # "Age: 25" (f-string, preferred)

# ValueError — invalid string for the target type
# int("hello")     # ValueError: invalid literal
# int("3.14")      # ValueError: must be whole number string
# Use: int(float("3.14")) for "3.14" → 3

# Safe conversion with error handling
user_input = "abc"
try:
    number = int(user_input)
except ValueError:
    print(f"Cannot convert '{user_input}' to int")

# Practical: safely read numeric input
age_str = input("Enter age: ")
try:
    age = int(age_str)
    print(f"You are {age} years old")
except ValueError:
    print("Please enter a valid number")