def main():
"""Main loop: Read and evaluate user's input."""
print(WELCOME)
while True:
# Read user's input
try:
expression = input(f"{PS1} ")
except (KeyboardInterrupt, EOFError):
raise SystemExit()
# Handle special commands
if expression.lower() == "help":
print(USAGE)
continue
if expression.lower() in {"quit", "exit"}:
raise SystemExit()
# Evaluate the expression and handle errors
try:
result = evaluate(expression)
except SyntaxError:
# If the user enters an invalid expression
print("Invalid input expression syntax")
continue
except (NameError, ValueError) as err:
# If the user tries to use a name that isn't allowed
print(err)
continue
# Print the result if no error occurs
print(result)
def test_evaluate_value_error(expression):
with pytest.raises(ValueError):
evaluate(expression)
def test_evaluate_syntax_error(expression):
with pytest.raises(SyntaxError):
evaluate(expression)
def test_evaluate_name_error(expression):
with pytest.raises(NameError):
evaluate(expression)
def test_evaluate(expression, expected):
assert evaluate(expression) == expected