cohesion 0.9.0

A tool for measuring Python class cohesion.

# Cohesion

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Cohesion is a tool for measuring Python class cohesion.

> In computer programming, cohesion refers to the degree to which the elements
> of a module belong together. Thus, cohesion measures the strength of
> relationship between pieces of functionality within a given module. For
> example, in highly cohesive systems functionality is strongly related.
> - [Wikipedia](https://en.wikipedia.org/wiki/Cohesion_(computer_science))

> When cohesion is high, it means that the methods and variables of the class
> are co-dependent and hang together as a logical whole.
> - Clean Code pg. 140

Some of the advantages of high cohesion, also by Wikipedia:

* Reduced module complexity (they are simpler, having fewer operations).
* Increased system maintainability, because logical changes in the domain
affect fewer modules, and because changes in one module require fewer
changes in other modules.
* Increased module reusability, because application developers will find
the component they need more easily among the cohesive set of operations
provided by the module.

# Installing

```
$ pip install cohesion
$ cohesion -h
```

OR

```
$ git clone https://github.com/mschwager/cohesion.git
$ cd cohesion
$ PYTHONPATH=lib/ python -m cohesion -h
```

# Using

`Cohesion` measures class and instance variable usage across the methods
of that class.

```
$ cat example.py
class ExampleClass1(object):
class_variable1 = 5
class_variable2 = 6

def func1(self):
self.instance_variable = 6

def inner_func(b):
return b + 5

local_variable = self.class_variable1

return local_variable

def func2(self):
print(self.class_variable2)

@staticmethod
def func3(variable):
return variable + 7

class ExampleClass2(object):
def func1(self):
self.instance_variable1 = 7
```

```
$ cohesion --files example.py --verbose
File: example.py
Class: ExampleClass1 (1:0)
Function: func1 2/3 66.67%
Variable: class_variable1 True
Variable: class_variable2 False
Variable: instance_variable True
Function: func2 1/3 33.33%
Variable: class_variable1 False
Variable: class_variable2 True
Variable: instance_variable False
Function: func3 0/3 0.00%
Variable: class_variable1 False
Variable: class_variable2 False
Variable: instance_variable False
Total: 33.33%
Class: ExampleClass2 (23:0)
Function: func1 1/1 100.00%
Variable: instance_variable1 True
Total: 100.00%
```

The `--below` and `--above` flags can be specified to only show classes with
a cohesion value below or above the specified percentage, respectively.

## Flake8 Support

You can now lint Python files for classes with low cohesion with `flake8`!
First, ensure your installation has registered `cohesion`:

```
$ flake8 --version
3.2.1 (pyflakes: 1.0.0, cohesion: 0.8.0, pycodestyle: 2.2.0, mccabe: 0.5.3) CPython 2.7.12 on Linux
```

And now use `flake8` to lint your file with the extension enabled:

```
$ flake8 --enable-extension=H60 example.py
example.py:1:1: H601 class has low cohesion
```

## Python Versions

If you would like to simultaneously run `Cohesion` on Python 2 and Python 3
code then you will have to install it for both versions. I.e.

```
$ pip2 install cohesion
$ pip3 install cohesion
```

Then use the corresponding version to run the module:

```
$ python2 -m cohesion --files python2_file.py
$ python3 -m cohesion --files python3_file.py
```

# Developing

First, install development packages:

```
$ pip install -r requirements-dev.txt
```

## Testing

```
$ nose2
```

## Linting

```
$ flake8
```

## Coverage

```
$ nose2 --with-coverage
```