Cohesion metrics measure how well methods of a class are related to each other. A cohesive class has one responsibility. A non-cohesive class has more unrelated functions, thus more than one responsibility.

LCOM4 considers method as related with other method, when both of them use common attribute or method call. Methods are not compared with constructors / initializers eg. __init__, since they often involve all attributes. Also all inherited methods are ignored - as they come from different class.

Score:

• ==1 - indicates a cohesive class, which is the "good" class;
• >=2 - indicates a problem. The class should be split into so many smaller classes;
• ==0 - happens when there are no methods in a class. This is also a "bad" class.

Just point it to a module or a package that needs to be measured:

bin/lcom src

This will result in such output:

Calculating LCOM using LCOM4
+---------------------------------+------+
| Method                          | LCOM |
+---------------------------------+------+
| src.command.FileSystem          | 1    |
| src.command.LCOMFactory         | 0    |
| src.command.Printer             | 0    |
| src.command.PrinterFactory      | 0    |
| src.command.Runner              | 1    |
| src.command.STDOut              | 0    |
| src.lcom.LCOM4                  | 1    |
| src.lcom.LCOMAlgorithm          | 0    |
| src.reflection.ClassReflection  | 1    |
| src.reflection.MethodReflection | 1    |
| src.reflection.ModuleReflection | 1    |
| src.reflection.Reflection       | 0    |
| src.reflection.ReflectionError  | 0    |
+---------------------------------+------+
| Average                         | 0.46 |
+---------------------------------+------+

It is also possible to measure single module:

bin/lcom src/command.py

Or mix them:

bin/lcom src/command.py tests