## Problem Implement a function that expands `${VARIABLE}` placeholders in a template string using a provided variable map. Undefined variables should raise an error. Nested expansions (a variable whose value contains another `${...}`) should be recursively resolved up to a max depth. ```python def expand_variables( template: str, variables: dict[str, str], max_depth: int = 10 ) -> str: pass ``` **Example:** ``` variables = {"NAME": "Alice", "GREETING": "Hello, ${NAME}!", "CITY": "NYC"} expand_variables("${GREETING} From ${CITY}.", variables) -> "Hello, Alice! From NYC." expand_variables("Hi ${UNKNOWN}", variables) -> raises KeyError or UndefinedVariableError # Cycle: A -> "${B}", B -> "${A}" -> raises RecursionDepthError after max_depth ``` ## Follow-ups 1. How do you detect cycles in variable expansion, and what error do you raise? 2. How would you support default values with `${VAR:-default}` syntax (similar to bash)? 3. What is the difference between eager expansion (expand everything at parse time) and lazy expansion (expand at use time)? 4. How would you make the function safe against injection attacks if variable values come from untrusted user input?

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Variable Expansion: Implement Shell-Style Variable Substitution in a Template String

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Problem Implement a function that expands ${VARIABLE} placeholders in a template string using a provided variable map. Undefined variables should raise an error. Nested expansions (a variable whose value contains another ${...}) should be recursively resolved up to a max depth. Example: Follow-ups How do you detect cycles in variable expansion, and what error do you raise? How would you support default values with ${VAR:-default} syntax (similar to bash)? What is the difference between eager exp…

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This is a candidate experience report from a rubrik interview during the phone round.

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Variable Expansion: Implement Shell-Style Variable Substitution in a Template String

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