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Evaluate arithmetic with correct precedence and parentheses

Write your own parser for + - * /, unary minus and parentheses. Using eval() or a math library isn't allowed.evaluate(expr) should handle + - * /, unary minus, nested parentheses and decimals. * and / bind tighter than + and -, and operators of the same rank apply left to right. Today 2 + 3 * 4 returns 20, (2 + 3) * 4 crashes and 2 + returns a number. Malformed input and division by zero must raise EvalError, and no other exception should escape. Parse the expression yourself: eval, exec, compile and expression libraries are not allowed. SPEC.md has the full grammar.

45 min

python

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You're done when

Ordinary expressions give the right value, including decimals and any amount of spacing.
* and / bind tighter than + and -, and parentheses override that.
Unary minus works at the start of an expression, after an operator and in front of a parenthesised group.
Malformed input such as 2 +, (1 + 2 or an empty string raises EvalError.
Division by zero raises EvalError, including through a sub-expression like 5 / (2 - 2).

What it measures

Parser designHow the parser encodes precedence and left-to-right grouping.

Edge casesWhether unary minus, nested parentheses and every error case are covered.

Own implementationWhether the evaluation is written by hand, without `eval` or an expression library.

Your environment

Terminal + editorA full shell in the browser

Claude CodePre-authenticated, no key setup

Isolated microVMYours alone, wiped afterwards

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45 min

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