FIT9136 Chap.3 Functions, Scope and Dictionaries

Functions, Scope and Dictionaries

Define function contract

The course material gives this chapter a concrete anchor: Week 4 combines function design, namespaces, scoping and dictionaries as a modularity step. That function contract anchor controls how scope is explained and how dictionary is tested in changed practice.

Functions, Scope and Dictionaries turns function contract, scope and dictionary into executable reasoning.

The chapter's practical target is to decompose a task into functions with local state and dictionary-based lookup, so every explanation should connect syntax to program state, control flow and observable output.

Treat function contract as a precise program object, not a loose label. Identify the value or responsibility of function contract before execution, then trace what can read it, change it or depend on it.

This makes state changes visible before they become debugging guesses.

Use scope to explain the program's next move. Work through one representative scope input by hand and name the branch, iteration or call that follows. If the scope trace cannot be stated, the code may run by accident rather than by understood design.

Bring in dictionary as the test of structure.

Compare normal, boundary and invalid inputs for dictionary; state the expected behaviour first; then use the mismatch between expectation and result to localise the defect.

For the application — decompose a task into functions with local state and dictionary-based lookup — write the smallest complete example that exposes the rule.

Explain why the dictionary result works, what would break it and how the program should signal or recover from that failure.

Trace scope

Before running an example involving function contract, make a trace table with the important state before and after each operation. Include the value associated with function contract, the control decision governed by scope and the output or object affected by dictionary.

The function contract table turns an unexplained result into a sequence that can be tested one transition at a time.

Test three inputs: an ordinary case, a boundary case and an invalid case. State the expected dictionary result for each before execution, then compare it with what the program actually does.

A useful test of scope isolates one rule; changing several conditions at once cannot reveal which condition caused the failure.

Practise explaining the solution without reading the code. For fit9136, name the data representation, the control flow, the responsibility of each function or class and the reason the chosen design supports decompose a task into functions with local state and dictionary-based lookup.

This dictionary rehearsal matters when a written test or interview asks why the program works rather than whether it produces one correct output.

A complete response should make the task visible before the detail: identify what must be decided, define the relevant terms, connect the evidence to scope, and use dictionary to test the result.

The final sentence about dictionary should answer the question actually asked rather than merely repeat the topic.

The controlling limit is specific: A function that depends on undeclared global state is difficult to test and reuse.

Keep that dictionary limit beside the worked example, because it separates a careful fit9136 answer from one that sounds confident but claims more than the task or evidence supports.

For revision, retrieve function contract, scope and dictionary without notes, explain their relationship aloud, then complete a changed version of the application: decompose a task into functions with local state and dictionary-based lookup.

Record the first failed scope reasoning move and repair it before attempting another case.

What this chapter covers

• 01

  function contract

• 02

  scope

• 03

  dictionary

• 04

  Applying function contract

• 05

  Limits of scope and dictionary

Count words with a dictionary

Key terms

function contract

Statement of accepted inputs, returned result, side effects and exceptional conditions. This chapter uses the concept when students decompose a task into functions with local state and dictionary-based lookup. Use this definition when the task is to decompose a task into functions with local state and dictionary-based lookup.

scope

Region in which a name binding is visible and can be resolved. It helps explain the reasoning required to decompose a task into functions with local state and dictionary-based lookup. Use this definition when the task is to decompose a task into functions with local state and dictionary-based lookup.

dictionary

Mutable mapping from unique hashable keys to values. Its limit matters because a function that depends on undeclared global state is difficult to test and reuse. Use this definition when the task is to decompose a task into functions with local state and dictionary-based lookup.

Functions, Scope and Dictionaries FAQ

Assessment move

Reconstruct the relationship among function contract, scope and dictionary; complete the chapter application without notes; then test the result against this limit: A function that depends on undeclared global state is difficult to test and reuse.

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