Key parameter
A key parameter is a function argument that accepts a callable for deriving comparison or selection values from data items.
Python Workout: 50 ten-minute exercises
A parameter accepted by sorting functions that specifies a callable for extracting comparison keys from items.
- How it is used
- Uses callable key extraction to customize sorted ordering for built-in data structures.
- How deep it goes
- Explains per-element key invocation and demonstrates tuple keys, lambdas, and itemgetter, without examining sorting internals.
- Examples
- Demonstrates alphabetizing dictionaries by last and first names, then proposes absolute-value, vowel-count, and nested-sum orderings.
- What you can do after
- Apply it via sorted with regular functions, lambdas, tuple keys, or itemgetter.
Read how Python Workout: 50 ten-minute exercises explains key parameter →
Python How-To
A key parameter is a sorting or selection parameter that accepts a callable for deriving a comparison value from each item.
- How it is used
- Deploys callables to derive comparison values for sorting lists, iterables, and selection functions such as max and min.
- How deep it goes
- Explains one-argument key callables, derived comparison values, lambdas, and custom classes, but stops short of callable implementation generally.
- Examples
- Uses mixed-type values, urgency-ranked task dictionaries, description lengths, and poker cards to demonstrate derived ordering.
- What you can do after
- Apply it via sort or sorted to order records by extracted fields, choose lambdas for small jobs, and build callable domain mappings.
Related concepts
- lambdaused by · A lambda is a language construct that defines an unnamed function or callable, often as a value.
- __str__used by · __str__ is a Python special method that returns an object's informal, human-readable string representation.
- callableused by · A callable is an object that can be invoked using function-call syntax.
- sortedconfigures · sorted is a Python built-in function that returns a new list containing an iterable’s elements in sorted order without modifying the original iterable.
- sorting algorithmconfigures · A sorting algorithm is a procedure that rearranges elements of a collection into an order determined by an ordering criterion.
- functionused by · A function is a callable program unit that performs an operation, may accept inputs, and can produce a result or side effect.
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