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.