py-05-calc
0.800
Challenge · difficulty 5/5
# Arithmetic Expression Evaluator
Implement a file **`solution.py`** containing a function:
```python
def evaluate(expr: str) -> float:
...
```
Evaluate an arithmetic expression given as a string and return its value as a
`float`.
Supported syntax:
- Binary operators `+`, `-`, `*`, `/` with standard precedence
(`*` and `/` bind tighter than `+` and `-`) and left-to-right associativity.
- Parentheses `(` ... `)` for grouping.
- Unary plus and minus, e.g. `-3`, `-(2 + 1)`, `2 * -3`.
- Integer and float literals, e.g. `42`, `3.14`, `.5`, `10.`.
- Arbitrary surrounding / internal whitespace, which is ignored.
Requirements:
- Return the numeric result as a `float`. For example
`evaluate("1 + 2 * 3") == 7.0` and `evaluate("(1 + 2) * 3") == 9.0`.
- Implement a real parser/evaluator that respects precedence and parentheses.
**Do not** use `eval`, `exec`, or similar (the harness may inspect for this).
- Raise `ValueError` on malformed input. Malformed includes: empty / whitespace-only
input, unbalanced parentheses, a missing operand or operator (e.g. `"1 +"`,
`"1 2"`, `"* 3"`), and unexpected characters.
- Division by zero should raise an error (a `ZeroDivisionError` or `ValueError`
is acceptable).
Examples:
```python
evaluate("2 + 3 * 4") # 14.0
evaluate("(2 + 3) * 4") # 20.0
evaluate("10 / 4") # 2.5
evaluate("-3 + 2") # -1.0
evaluate("2 * (1 + -1.5)") # -1.0
```
tests/test_calc.py
import pytest
from solution import evaluate
def test_simple_addition():
assert evaluate("1 + 2") == 3.0
def test_precedence():
assert evaluate("2 + 3 * 4") == 14.0
assert evaluate("1 + 2 * 3") == 7.0
def test_parentheses_override_precedence():
assert evaluate("(2 + 3) * 4") == 20.0
assert evaluate("(1 + 2) * 3") == 9.0
def test_division_is_float():
assert evaluate("10 / 4") == 2.5
assert isinstance(evaluate("4 / 2"), float)
def test_unary_minus():
assert evaluate("-3 + 2") == -1.0
assert evaluate("2 * -3") == -6.0
assert evaluate("-(2 + 1)") == -3.0
def test_float_and_whitespace():
assert evaluate(" 3.14 + .86 ") == pytest.approx(4.0)
assert evaluate("10. / 4") == 2.5
def test_left_associativity():
assert evaluate("10 - 2 - 3") == 5.0
assert evaluate("100 / 5 / 2") == 10.0
def test_nested_parens():
assert evaluate("2 * (1 + (3 - 1) * 2)") == 10.0
def test_malformed_raises_value_error():
for bad in ["", " ", "1 +", "* 3", "1 2", "(1 + 2", "1 + 2)", "1 + * 2", "3 $ 4"]:
with pytest.raises(ValueError):
evaluate(bad)
def test_division_by_zero_raises():
with pytest.raises((ValueError, ZeroDivisionError)):
evaluate("1 / 0")
System prompt
You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.Proposed solution
```python
def evaluate(expr: str) -> float:
import re
# Remove all whitespace
expr = expr.replace(' ', '')
if not expr:
raise ValueError("Empty input")
# Tokenize the expression
tokens = []
i = 0
n = len(expr)
while i < n:
c = expr[i]
if c in '()+-*/':
tokens.append(c)
i += 1
elif c.isdigit() or c == '.':
j = i
has_decimal = False
while j < n and (expr[j].isdigit() or expr[j] == '.'):
if expr[j] == '.':
if has_decimal:
raise ValueError("Invalid number format")
has_decimal = True
j += 1
num_str = expr[i:j]
if num_str == '.':
num_str = '0.'
elif num_str.endswith('.'):
num_str += '0'
tokens.append(num_str)
i = j
else:
raise ValueError(f"Unexpected character: {c}")
# Check for empty tokens or invalid sequences
if not tokens:
raise ValueError("Empty input")
# Handle unary operators
processed_tokens = []
i = 0
n = len(tokens)
while i < n:
token = tokens[i]
if token in '+-' and (i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/'):
# It's a unary operator
if i + 1 >= n:
raise ValueError("Missing operand after unary operator")
next_token = tokens[i+1]
if next_token in '+-*/':
raise ValueError("Missing operand after unary operator")
processed_tokens.append(token + next_token)
i += 2
else:
processed_tokens.append(token)
i += 1
# Convert numbers to floats
for i, token in enumerate(processed_tokens):
if token not in '+-*/()' and not token.startswith(('+', '-')):
try:
processed_tokens[i] = float(token)
except ValueError:
raise ValueError(f"Invalid number: {token}")
# Shunting-yard algorithm to convert to RPN
output = []
operators = []
precedence = {'+': 1, '-': 1, '*': 2, '/': 2}
for token in processed_tokens:
if isinstance(token, float):
output.append(token)
elif token in precedence:
while (operators and operators[-1] != '(' and
precedence[operators[-1]] >= precedence[token]):
output.append(operators.pop())
operators.append(token)
elif token == '(':
operators.append(token)
elif token == ')':
if not operators or operators[-1] == '(':
raise ValueError("Mismatched parentheses")
while operators[-1] != '(':
output.append(operators.pop())
operators.pop() # Remove the '('
else:
# Handle unary operators
if token.startswith(('+', '-')):
op = token[0]
num = token[1:]
if not output:
raise ValueError("Missing operand for unary operator")
val = output.pop()
if op == '-':
val = -val
output.append(val)
while operators:
if operators[-1] == '(':
raise ValueError("Mismatched parentheses")
output.append(operators.pop())
# Evaluate RPN
stack = []
for token in output:
if isinstance(token, float):
stack.append(token)
else:
if len(stack) < 2:
raise ValueError("Missing operand for operator")
b = stack.pop()
a = stack.pop()
if token == '+':
stack.append(a + b)
elif token == '-':
stack.append(a - b)
elif token == '*':
stack.append(a * b)
elif token == '/':
if b == 0:
raise ZeroDivisionError("Division by zero")
stack.append(a / b)
if len(stack) != 1:
raise ValueError("Malformed expression")
return stack[0]
```Test output (stdout)
len(expr)
while i < n:
c = expr[i]
if c in '()+-*/':
tokens.append(c)
i += 1
elif c.isdigit() or c == '.':
j = i
has_decimal = False
while j < n and (expr[j].isdigit() or expr[j] == '.'):
if expr[j] == '.':
if has_decimal:
raise ValueError("Invalid number format")
has_decimal = True
j += 1
num_str = expr[i:j]
if num_str == '.':
num_str = '0.'
elif num_str.endswith('.'):
num_str += '0'
tokens.append(num_str)
i = j
else:
raise ValueError(f"Unexpected character: {c}")
# Check for empty tokens or invalid sequences
if not tokens:
raise ValueError("Empty input")
# Handle unary operators
processed_tokens = []
i = 0
n = len(tokens)
while i < n:
token = tokens[i]
if token in '+-' and (i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/'):
# It's a unary operator
if i + 1 >= n:
raise ValueError("Missing operand after unary operator")
next_token = tokens[i+1]
if next_token in '+-*/':
raise ValueError("Missing operand after unary operator")
processed_tokens.append(token + next_token)
i += 2
else:
processed_tokens.append(token)
i += 1
# Convert numbers to floats
for i, token in enumerate(processed_tokens):
if token not in '+-*/()' and not token.startswith(('+', '-')):
try:
processed_tokens[i] = float(token)
except ValueError:
raise ValueError(f"Invalid number: {token}")
# Shunting-yard algorithm to convert to RPN
output = []
operators = []
precedence = {'+': 1, '-': 1, '*': 2, '/': 2}
for token in processed_tokens:
if isinstance(token, float):
output.append(token)
elif token in precedence:
while (operators and operators[-1] != '(' and
precedence[operators[-1]] >= precedence[token]):
output.append(operators.pop())
operators.append(token)
elif token == '(':
operators.append(token)
elif token == ')':
if not operators or operators[-1] == '(':
raise ValueError("Mismatched parentheses")
while operators[-1] != '(':
output.append(operators.pop())
operators.pop() # Remove the '('
else:
# Handle unary operators
if token.startswith(('+', '-')):
op = token[0]
num = token[1:]
if not output:
> raise ValueError("Missing operand for unary operator")
E ValueError: Missing operand for unary operator
solution.py:96: ValueError
______________________ test_malformed_raises_value_error _______________________
def test_malformed_raises_value_error():
for bad in ["", " ", "1 +", "* 3", "1 2", "(1 + 2", "1 + 2)", "1 + * 2", "3 $ 4"]:
> with pytest.raises(ValueError):
^^^^^^^^^^^^^^^^^^^^^^^^^
E Failed: DID NOT RAISE ValueError
test_calc.py:47: Failed
=========================== short test summary info ============================
FAILED test_calc.py::test_unary_minus - ValueError: Missing operand for unary...
FAILED test_calc.py::test_malformed_raises_value_error - Failed: DID NOT RAIS...
2 failed, 8 passed in 0.02s
Self-repair attempts
[
{
"total": 10,
"answer": "```python\ndef evaluate(expr: str) -> float:\n import re\n\n # Remove all whitespace\n expr = expr.replace(' ', '')\n\n if not expr:\n raise ValueError(\"Empty input\")\n\n # Tokenize the expression\n tokens = []\n i = 0\n n = len(expr)\n while i < n:\n c = expr[i]\n if c in '()+-*/':\n tokens.append(c)\n i += 1\n elif c.isdigit() or c == '.':\n j = i\n has_decimal = False\n while j < n and (expr[j].isdigit() or expr[j] == '.'):\n if expr[j] == '.':\n if has_decimal:\n raise ValueError(\"Invalid number format\")\n has_decimal = True\n j += 1\n num_str = expr[i:j]\n if num_str == '.':\n num_str = '0.'\n elif num_str.endswith('.'):\n num_str += '0'\n tokens.append(num_str)\n i = j\n else:\n raise ValueError(f\"Unexpected character: {c}\")\n\n # Check for empty tokens or invalid sequences\n if not tokens:\n raise ValueError(\"Empty input\")\n\n # Handle unary operators\n processed_tokens = []\n i = 0\n n = len(tokens)\n while i < n:\n token = tokens[i]\n if token in '+-' and (i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/'):\n # It's a unary operator\n if i + 1 >= n:\n raise ValueError(\"Missing operand after unary operator\")\n next_token = tokens[i+1]\n if next_token in '+-*/':\n raise ValueError(\"Missing operand after unary operator\")\n processed_tokens.append(token + next_token)\n i += 2\n else:\n processed_tokens.append(token)\n i += 1\n\n # Convert numbers to floats\n for i, token in enumerate(processed_tokens):\n if token not in '+-*/()' and not token.startswith(('+', '-')):\n try:\n processed_tokens[i] = float(token)\n except ValueError:\n raise ValueError(f\"Invalid number: {token}\")\n\n # Shunting-yard algorithm to convert to RPN\n output = []\n operators = []\n precedence = {'+': 1, '-': 1, '*': 2, '/': 2}\n\n for token in processed_tokens:\n if isinstance(token, float):\n output.append(token)\n elif token in precedence:\n while (operators and operators[-1] != '(' and\n precedence[operators[-1]] >= precedence[token]):\n output.append(operators.pop())\n operators.append(token)\n elif token == '(':\n operators.append(token)\n elif token == ')':\n if not operators or operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n while operators[-1] != '(':\n output.append(operators.pop())\n operators.pop() # Remove the '('\n else:\n # Handle unary operators\n if token.startswith(('+', '-')):\n op = token[0]\n num = token[1:]\n if not output:\n raise ValueError(\"Missing operand for unary operator\")\n val = output.pop()\n if op == '-':\n val = -val\n output.append(val)\n\n while operators:\n if operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n output.append(operators.pop())\n\n # Evaluate RPN\n stack = []\n for token in output:\n if isinstance(token, float):\n stack.append(token)\n else:\n if len(stack) < 2:\n raise ValueError(\"Missing operand for operator\")\n b = stack.pop()\n a = stack.pop()\n if token == '+':\n stack.append(a + b)\n elif token == '-':\n stack.append(a - b)\n elif token == '*':\n stack.append(a * b)\n elif token == '/':\n if b == 0:\n raise ZeroDivisionError(\"Division by zero\")\n stack.append(a / b)\n\n if len(stack) != 1:\n raise ValueError(\"Malformed expression\")\n\n return stack[0]\n```",
"passed": 8,
"test_error": "Missing operand after unary operator\")\n processed_tokens.append(token + next_token)\n i += 2\n else:\n processed_tokens.append(token)\n i += 1\n \n # Convert numbers to floats\n for i, token in enumerate(processed_tokens):\n if token not in '+-*/()' and not token.startswith(('+', '-')):\n try:\n processed_tokens[i] = float(token)\n except ValueError:\n raise ValueError(f\"Invalid number: {token}\")\n \n # Shunting-yard algorithm to convert to RPN\n output = []\n operators = []\n precedence = {'+': 1, '-': 1, '*': 2, '/': 2}\n \n for token in processed_tokens:\n if isinstance(token, float):\n output.append(token)\n elif token in precedence:\n while (operators and operators[-1] != '(' and\n precedence[operators[-1]] >= precedence[token]):\n output.append(operators.pop())\n operators.append(token)\n elif token == '(':\n operators.append(token)\n elif token == ')':\n if not operators or operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n while operators[-1] != '(':\n output.append(operators.pop())\n operators.pop() # Remove the '('\n else:\n # Handle unary operators\n if token.startswith(('+', '-')):\n op = token[0]\n num = token[1:]\n if not output:\n> raise ValueError(\"Missing operand for unary operator\")\nE ValueError: Missing operand for unary operator\n\nsolution.py:96: ValueError\n______________________ test_malformed_raises_value_error _______________________\n\n def test_malformed_raises_value_error():\n for bad in [\"\", \" \", \"1 +\", \"* 3\", \"1 2\", \"(1 + 2\", \"1 + 2)\", \"1 + * 2\", \"3 $ 4\"]:\n> with pytest.raises(ValueError):\n ^^^^^^^^^^^^^^^^^^^^^^^^^\nE Failed: DID NOT RAISE ValueError\n\ntest_calc.py:47: Failed\n=========================== short test summary info ============================\nFAILED test_calc.py::test_unary_minus - ValueError: Missing operand for unary...\nFAILED test_calc.py::test_malformed_raises_value_error - Failed: DID NOT RAIS...\n2 failed, 8 passed in 0.02s"
},
{
"total": 10,
"answer": "```python\ndef evaluate(expr: str) -> float:\n import re\n\n # Remove all whitespace\n expr = expr.replace(' ', '')\n\n if not expr:\n raise ValueError(\"Empty input\")\n\n # Tokenize the expression\n tokens = []\n i = 0\n n = len(expr)\n while i < n:\n c = expr[i]\n if c in '()+-*/':\n tokens.append(c)\n i += 1\n elif c.isdigit() or c == '.':\n j = i\n has_decimal = False\n while j < n and (expr[j].isdigit() or expr[j] == '.'):\n if expr[j] == '.':\n if has_decimal:\n raise ValueError(\"Invalid number format\")\n has_decimal = True\n j += 1\n num_str = expr[i:j]\n if num_str == '.':\n num_str = '0.'\n elif num_str.endswith('.'):\n num_str += '0'\n tokens.append(num_str)\n i = j\n else:\n raise ValueError(f\"Unexpected character: {c}\")\n\n # Check for empty tokens or invalid sequences\n if not tokens:\n raise ValueError(\"Empty input\")\n\n # Handle unary operators\n processed_tokens = []\n i = 0\n n = len(tokens)\n while i < n:\n token = tokens[i]\n if token in '+-' and (i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/'):\n # It's a unary operator\n if i + 1 >= n:\n raise ValueError(\"Missing operand after unary operator\")\n next_token = tokens[i+1]\n if next_token in '+-*/':\n raise ValueError(\"Missing operand after unary operator\")\n processed_tokens.append(token + next_token)\n i += 2\n else:\n processed_tokens.append(token)\n i += 1\n\n # Convert numbers to floats\n for i, token in enumerate(processed_tokens):\n if token not in '+-*/()' and not token.startswith(('+', '-')):\n try:\n processed_tokens[i] = float(token)\n except ValueError:\n raise ValueError(f\"Invalid number: {token}\")\n\n # Shunting-yard algorithm to convert to RPN\n output = []\n operators = []\n precedence = {'+': 1, '-': 1, '*': 2, '/': 2}\n\n for token in processed_tokens:\n if isinstance(token, float):\n output.append(token)\n elif token in precedence:\n while (operators and operators[-1] != '(' and\n precedence[operators[-1]] >= precedence[token]):\n output.append(operators.pop())\n operators.append(token)\n elif token == '(':\n operators.append(token)\n elif token == ')':\n if not operators or operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n while operators[-1] != '(':\n output.append(operators.pop())\n operators.pop() # Remove the '('\n else:\n # Handle unary operators\n if token.startswith(('+', '-')):\n op = token[0]\n num = token[1:]\n if not output:\n raise ValueError(\"Missing operand for unary operator\")\n val = output.pop()\n if op == '-':\n val = -val\n output.append(val)\n\n while operators:\n if operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n output.append(operators.pop())\n\n # Evaluate RPN\n stack = []\n for token in output:\n if isinstance(token, float):\n stack.append(token)\n else:\n if len(stack) < 2:\n raise ValueError(\"Missing operand for operator\")\n b = stack.pop()\n a = stack.pop()\n if token == '+':\n stack.append(a + b)\n elif token == '-':\n stack.append(a - b)\n elif token == '*':\n stack.append(a * b)\n elif token == '/':\n if b == 0:\n raise ZeroDivisionError(\"Division by zero\")\n stack.append(a / b)\n\n if len(stack) != 1:\n raise ValueError(\"Malformed expression\")\n\n return stack[0]\n```",
"passed": 8,
"test_error": "Missing operand after unary operator\")\n processed_tokens.append(token + next_token)\n i += 2\n else:\n processed_tokens.append(token)\n i += 1\n \n # Convert numbers to floats\n for i, token in enumerate(processed_tokens):\n if token not in '+-*/()' and not token.startswith(('+', '-')):\n try:\n processed_tokens[i] = float(token)\n except ValueError:\n raise ValueError(f\"Invalid number: {token}\")\n \n # Shunting-yard algorithm to convert to RPN\n output = []\n operators = []\n precedence = {'+': 1, '-': 1, '*': 2, '/': 2}\n \n for token in processed_tokens:\n if isinstance(token, float):\n output.append(token)\n elif token in precedence:\n while (operators and operators[-1] != '(' and\n precedence[operators[-1]] >= precedence[token]):\n output.append(operators.pop())\n operators.append(token)\n elif token == '(':\n operators.append(token)\n elif token == ')':\n if not operators or operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n while operators[-1] != '(':\n output.append(operators.pop())\n operators.pop() # Remove the '('\n else:\n # Handle unary operators\n if token.startswith(('+', '-')):\n op = token[0]\n num = token[1:]\n if not output:\n> raise ValueError(\"Missing operand for unary operator\")\nE ValueError: Missing operand for unary operator\n\nsolution.py:96: ValueError\n______________________ test_malformed_raises_value_error _______________________\n\n def test_malformed_raises_value_error():\n for bad in [\"\", \" \", \"1 +\", \"* 3\", \"1 2\", \"(1 + 2\", \"1 + 2)\", \"1 + * 2\", \"3 $ 4\"]:\n> with pytest.raises(ValueError):\n ^^^^^^^^^^^^^^^^^^^^^^^^^\nE Failed: DID NOT RAISE ValueError\n\ntest_calc.py:47: Failed\n=========================== short test summary info ============================\nFAILED test_calc.py::test_unary_minus - ValueError: Missing operand for unary...\nFAILED test_calc.py::test_malformed_raises_value_error - Failed: DID NOT RAIS...\n2 failed, 8 passed in 0.02s"
},
{
"total": 10,
"answer": "```python\ndef evaluate(expr: str) -> float:\n import re\n\n # Remove all whitespace\n expr = expr.replace(' ', '')\n\n if not expr:\n raise ValueError(\"Empty input\")\n\n # Tokenize the expression\n tokens = []\n i = 0\n n = len(expr)\n while i < n:\n c = expr[i]\n if c in '()+-*/':\n tokens.append(c)\n i += 1\n elif c.isdigit() or c == '.':\n j = i\n has_decimal = False\n while j < n and (expr[j].isdigit() or expr[j] == '.'):\n if expr[j] == '.':\n if has_decimal:\n raise ValueError(\"Invalid number format\")\n has_decimal = True\n j += 1\n num_str = expr[i:j]\n if num_str == '.':\n num_str = '0.'\n elif num_str.endswith('.'):\n num_str += '0'\n tokens.append(num_str)\n i = j\n else:\n raise ValueError(f\"Unexpected character: {c}\")\n\n # Check for empty tokens or invalid sequences\n if not tokens:\n raise ValueError(\"Empty input\")\n\n # Handle unary operators\n processed_tokens = []\n i = 0\n n = len(tokens)\n while i < n:\n token = tokens[i]\n if token in '+-' and (i == 0 or tokens[i-1] == '(' or tokens[i-1] in '+-*/'):\n # It's a unary operator\n if i + 1 >= n:\n raise ValueError(\"Missing operand after unary operator\")\n next_token = tokens[i+1]\n if next_token in '+-*/':\n raise ValueError(\"Missing operand after unary operator\")\n processed_tokens.append(token + next_token)\n i += 2\n else:\n processed_tokens.append(token)\n i += 1\n\n # Convert numbers to floats\n for i, token in enumerate(processed_tokens):\n if token not in '+-*/()' and not token.startswith(('+', '-')):\n try:\n processed_tokens[i] = float(token)\n except ValueError:\n raise ValueError(f\"Invalid number: {token}\")\n\n # Shunting-yard algorithm to convert to RPN\n output = []\n operators = []\n precedence = {'+': 1, '-': 1, '*': 2, '/': 2}\n\n for token in processed_tokens:\n if isinstance(token, float):\n output.append(token)\n elif token in precedence:\n while (operators and operators[-1] != '(' and\n precedence[operators[-1]] >= precedence[token]):\n output.append(operators.pop())\n operators.append(token)\n elif token == '(':\n operators.append(token)\n elif token == ')':\n if not operators or operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n while operators[-1] != '(':\n output.append(operators.pop())\n operators.pop() # Remove the '('\n else:\n # Handle unary operators\n if token.startswith(('+', '-')):\n op = token[0]\n num = token[1:]\n if not output:\n raise ValueError(\"Missing operand for unary operator\")\n val = output.pop()\n if op == '-':\n val = -val\n output.append(val)\n\n while operators:\n if operators[-1] == '(':\n raise ValueError(\"Mismatched parentheses\")\n output.append(operators.pop())\n\n # Evaluate RPN\n stack = []\n for token in output:\n if isinstance(token, float):\n stack.append(token)\n else:\n if len(stack) < 2:\n raise ValueError(\"Missing operand for operator\")\n b = stack.pop()\n a = stack.pop()\n if token == '+':\n stack.append(a + b)\n elif token == '-':\n stack.append(a - b)\n elif token == '*':\n stack.append(a * b)\n elif token == '/':\n if b == 0:\n raise ZeroDivisionError(\"Division by zero\")\n stack.append(a / b)\n\n if len(stack) != 1:\n raise ValueError(\"Malformed expression\")\n\n return stack[0]\n```",
"passed": 8,
"test_error": ""
}
]