Resolve variable references

Medium~20 min

Configuration values may reference other variables as ${NAME}. Resolve every value recursively:

References to variables defined in variables are replaced by their resolved value.
References to undefined names resolve to the empty string.
If resolving a variable would require itself (directly or through others), return None for the whole result.

Return the dictionary of fully resolved values.

Function

Implement resolve. Input: variables: dict[str, str]. Returns: dict[str, str] | None.

>>> resolve({'URL': 'postgres://${HOST}:${PORT}/${DB_NAME}', 'HOST': 'db', 'PORT': '5432'})

{'URL': 'postgres://db:5432/', 'HOST': 'db', 'PORT': '5432'}

>>> resolve({'A': '${B}', 'B': '${A}'})

None

Level: API integration against fakes, data processing, error handling, decorators and asyncio. Several cooperating parts.
Roles: DevOps Engineer, Infrastructure Automation Engineer, Platform Engineer
Topics: Files and configuration, Graphs, Parsing text
Tests: 2 public (run with Run), 3 hidden (graded on Submit)
Grading: Exact match of the return value

Configuration values may reference other variables as ${NAME}. Resolve every value recursively:

References to variables defined in variables are replaced by their resolved value.
References to undefined names resolve to the empty string.
If resolving a variable would require itself (directly or through others), return None for the whole result.

Return the dictionary of fully resolved values.

Implement resolve. Input: variables: dict[str, str]. Returns: dict[str, str] | None.

>>> resolve({'URL': 'postgres://${HOST}:${PORT}/${DB_NAME}', 'HOST': 'db', 'PORT': '5432'})

{'URL': 'postgres://db:5432/', 'HOST': 'db', 'PORT': '5432'}

>>> resolve({'A': '${B}', 'B': '${A}'})

None

Level: API integration against fakes, data processing, error handling, decorators and asyncio. Several cooperating parts.
Roles: DevOps Engineer, Infrastructure Automation Engineer, Platform Engineer
Topics: Files and configuration, Graphs, Parsing text
Tests: 2 public (run with Run), 3 hidden (graded on Submit)
Grading: Exact match of the return value

Python 3.13

def resolve(variables: dict[str, str]):
    return dict(variables)

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Resolve variable references · Python practice