Python · Theory

raise

Theory

64/268

raise

raise throws an error when your rule is broken. if age < 0: raise ValueError("age cannot be negative"). The caller can except it. Use a clear message. You can raise built-in types or a small custom class. This is how a function refuses bad input instead of returning a magic -1.

Tiny validation + raise ValueError is the fresher pattern. Don’t raise Exception("error") for everything — name the type.

Output — amount must be > 0. raise stops the function; except prints the message.

Diagram

try:  10 / 0
         │ ZeroDivisionError
         ▼
  except → Cannot divide
         │
         ▼
      finally

Exam tip

if age < 0: raise ValueError(...).

Example

# raise
def deposit(amt):
    if amt <= 0:
        raise ValueError("amount must be > 0")
    return amt

try:
    deposit(-10)
except ValueError as e:
    print(e)

Output: amount must be > 0. raise stops the function; except prints the message.

Short notes

Defraise Error("msg").
RuleValidate early.
RememberClear message.

Python · Theory

raise

← All stacks

Theory

64/268

raise

Tiny validation + raise ValueError is the fresher pattern. Don’t raise Exception("error") for everything — name the type.

Output — amount must be > 0. raise stops the function; except prints the message.

Diagram

try:  10 / 0
         │ ZeroDivisionError
         ▼
  except → Cannot divide
         │
         ▼
      finally

Exam tip

if age < 0: raise ValueError(...).

Example

# raise
def deposit(amt):
    if amt <= 0:
        raise ValueError("amount must be > 0")
    return amt

try:
    deposit(-10)
except ValueError as e:
    print(e)

Output: amount must be > 0. raise stops the function; except prints the message.

Short notes

Defraise Error("msg").
RuleValidate early.
RememberClear message.

raise

Example

Short notes

Questions

raise

Example

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Questions