Code metrics

The static measures of a piece of code and their usual thresholds: lines of code, cyclomatic complexity, cognitive complexity, coupling, cohesion, duplication, technical debt, and what a metric does not tell you.

28 cards
6 topics
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Cyclomatic complexity: what is it?
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The number of independent paths through a function's control-flow graph: the number of decision points, plus one.
It gives the minimum number of tests needed to cover each independent path. McCabe recommends staying under 10: beyond that, the function becomes hard to test.
What is the cyclomatic complexity of this function? Count if, elif, for, while, and, or, then add 1.

```python
def classer(notes, seuil):
total = 0
for n in notes:
if n < 0 or n > 20:
continue
if n >= seuil:
total += 1
elif n >= seuil - 2 and n > 5:
total += 0.5
return total
`
- 7
- 5
- 6
- 9
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7
Six decision points: for, if, or, if, elif, and. Plus 1 makes 7. Forgetting the or and and operators, which each create a branch, gives 5; forgetting the +1 gives 6.
On a control-flow graph with E edges and N nodes, the cyclomatic complexity is ….
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On a control-flow graph with E edges and N nodes, the cyclomatic complexity is E − N + 2.
For a function with no decision, there are N − 1 edges and the formula gives 1: a single path. Each decision adds one more edge than nodes, hence 1 to the complexity.
Cognitive complexity: what is it?
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A measure of the effort needed to understand a function, which penalises breaks in flow and above all their nesting.
Ten if statements in a row are easy to read; ten nested if statements are not, yet the cyclomatic complexity is the same. The cognitive one tells them apart.

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