Chainee

What is this?

Chainee is a simple chaining tool for your predicates.

Chain any number of predicates as deep as you want, and visualize it.

Installation

pip install --user chainee

Usage

Everything is based on P object (from chainee import P), you simply wrap your predicates with P and start chaining it. E.g:

from chainee import P

def validate_name_length(name):
    """Check that name has at least 4 characters"""
    return len(name) > 3

def validate_name_lower(name):
    """Make sure that name is in lower case"""
    return name.islower()

chain = P(validate_name_length) & P(validate_name_lower)
print(chain("yaroslav"))  # True

As you can see, it's very easy and readable.

You can achieve any nesting level, the following is possible:

chain = ~((P(validate_name_length) & ~P(validate_name_lower)) | (P(validate_name_length) & P(validate_name_lower)))

You have a few operators you can use, & (and), | (or) and ~ (not). Basically that's all Chainee gets you, which is quite enough.

Visualizing

You can build a tree from your chain. Let's build a tree for the chain above:

>>> print(chain)
InvertedUnion(union=UnionOr(lhs=UnionAnd(lhs=Predicate(func=<function validate_name_length at 0x10fa4f160>, description='Check that name has at least 4 characters'), rhs=InvertedPredicate(func=<function validate_name_lower at 0x10fbcb8b0>, description='Make sure that name is in lower case')), rhs=UnionAnd(lhs=Predicate(func=<function validate_name_length at 0x10fa4f160>, description='Check that name has at least 4 characters'), rhs=Predicate(func=<function validate_name_lower at 0x10fbcb8b0>, description='Make sure that name is in lower case'))))
# note that doc strings copied into description

Now, lets build an actual tree:

>>> tree = chain.to_tree()
>>> print(tree)
NOT
└── OR
    ├── AND
    │   ├── Predicate(validate_name_lower)
    │   └── Predicate(validate_name_length)
    └── AND
        ├── NOT Predicate(validate_name_lower)
        └── Predicate(validate_name_length)

You can convert it into a picture as well:

>>> tree.to_picture("tree.png")

Which gives us the following: