Cyclomatic Complexity corresponds to the number of decisions a block of code contains plus 1. This number (also called McCabe number) is equal to the number of linearly independent paths through the code. This number can be used as a guide when testing conditional logic in blocks.
Radon analyzes the AST tree of a Python program to compute Cyclomatic Complexity. Statements have the following effects on Cyclomatic Complexity:
Construct
Effect on CC
Reasoning
if
+1
An if statement is a single decision.
elif
+1
The elif statement adds another decision.
else
+0
The else statement does not cause a new decision. The decision is at the if.
for
+1
There is a decision at the start of the loop.
while
+1
There is a decision at the while statement.
except
+1
Each except branch adds a new conditional path of execution.
finally
+0
The finally block is unconditionally executed.
with
+1
The with statement roughly corresponds to a try/except block (see PEP 343 for details).
assert
+1
The assert statement internally roughly equals a conditional statement.
Comprehension
+1
A list/set/dict comprehension of generator expression is equivalent to a for loop.
Boolean Operator
+1
Every boolean operator (and, or) adds a decision point.
Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:
Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.
When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).
Tuning
This issue has a mass of 35.
We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.
The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.
If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.