Commenting sucks so let your code do it for you with Guava like preconditions that also actually do something.

## Project description

Commenting sucks so let your code do it for you with preconditions that actually do something.

Examples:

```from pyconditions.pre import *

@Between("b", 1, 10)
def divideAbyB(a, b)
return a / b

@NotNone("a")
@Between("a", "a", "n")
@NotNone("b")
@Between("b", "n", "z")
def concat(a, b):
return a + b

@Custom("a", lambda x: x % 2 == 0)
@Custom("b", lambda x: not x % 2 == 0)
def evenOdd(a, b):
return a * b
```

The documenting is there with the code it self, and if you violate the preconditions then a PyCondition exception is thrown with a much nicer error message than broken code.

```evenOdd(3, 1)
```
```pyconditions.exceptions.PyCondition: 3 did not pass the custom condition for parameter 'a' in function evenOdd
```

```from pyconditions.post import *

@NotNone()
def test(a):
return a

@Custom(lambda a: a % 2 == 0)
def even(a):
return a
```
```test( None )
```
```pyconditions.exception.PyCondition: The return value for uber.awesome.project.test was None
```

You can also mix the two as well.

```from pyconditions import pre
from pyconditions import post

@pre.Custom("a", lamda a: a % 2 == 0)
@post.Custom(lambda a: a % 2 == 0)
def superSafeEven(a):
return a
```

Want some class invariant shenanigans?

```from pyconditions.invariant import Invariant, FieldsNotNone

@FieldsNotNone(["test"])
class Test:

def __init__(self):
self.test = 1

return self.test + 1

def set(self, v):
self.test = v

t = Test()
t.set(None)
```

That last call to add will cause the invariant to fail and thus throw the following:

```pyconditions.exceptions.PyCondition: Field "test" was None when it should not have been in invariant "notNone"
```

Need a custom invariant?

```from pyconditions.invariant import CustomInvariant

def invariant(self):
return self.test == 1

@CustomInvariant("test", invariant)
class Test(object):

def __init__(self):
self.test = 1

def method1(self):
self.test
```

This is great but the conditions slow my code down a lot? No problem.

```from pyconditions.stage import Stage

stage = Stage()
stage.prod()
```

Just set that somewhere in your code and you’ll be fine. There is still some overhead, mainly there will be two function calls for each method, the wrapper and the original function. But, for stacked Preconditions and Invariants it will not execute into the other conditions and invraiants when prod is called. If you want to go back to Dev then call dev().

Have conditions you want added? Open a PR with code.

Have an issue? Open a PR with fixed code.