Try/Except: Error Handling

number = 10 / 0  # ZeroDivisionError: division by zero

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

# ValueError — invalid value
try:
    age = int("twenty")
except ValueError:
    print("Please enter a number!")

# FileNotFoundError — file not found
try:
    with open("missing.txt") as f:
        data = f.read()
except FileNotFoundError:
    print("File not found!")

# KeyError — key missing from dict
try:
    age = user["age"]
except KeyError:
    print("Key 'age' is missing!")

# TypeError — incompatible types
try:
    result = "5" + 10
except TypeError:
    print("Incompatible types!")

# IndexError — index out of range
try:
    print([1, 2, 3][10])
except IndexError:
    print("Index out of range!")

try:
    age = int(input("Age: "))
    result = 100 / age
except ValueError:
    print("Please enter a number!")
except ZeroDivisionError:
    print("Age cannot be zero!")
except Exception as e:          # catch everything else
    print(f"Unexpected error: {e}")

try:
    data = json.loads(json_string)
except json.JSONDecodeError as e:
    print(f"Invalid JSON: {e}")
else:
    process(data)               # runs only on success
finally:
    print("Always runs")        # cleanup

# ❌ Bad — hiding bugs
try:
    hacky_code()
except:
    pass

# ❌ Bad — replacing checks
try:
    if user["age"] > 18: ...
except KeyError:
    ...

# ✅ Good — check first
if "age" in user and user["age"] > 18: ...

# User input
def get_int(prompt):
    while True:
        try:
            return int(input(prompt))
        except ValueError:
            print("Please enter a whole number.")

# Files
try:
    with open("config.json") as f:
        config = json.load(f)
except FileNotFoundError:
    config = {}

# Network / API
try:
    response = requests.get(url, timeout=5)
except (ConnectionError, TimeoutError):
    print("Server unavailable")