Dynamically add methods to a class in Python 3.0

Question

I\'m trying to write a Database Abstraction Layer in Python which lets you construct SQL statments using chained function calls such as:

results = db.search(\"bo         


        

Answer 1

Here is some working code to get you started (not the whole program you were trying to write, but something that shows how the parts can fit together):

class Assign:

    def __init__(self, searchobj, key):
        self.searchobj = searchobj
        self.key = key

    def __call__(self, value):
        self.searchobj.conditions[self.key] = value
        return self.searchobj

class Book():

    def __init__(self, family):
        self.family = family
        self.options = ['price', 'name', 'author', 'genre']
        self.conditions = {}

    def __getattr__(self, key):
        if key in self.options:
            return Assign(self, key)
        raise RuntimeError('There is no option for: %s' % key)

    def execute(self):
        # XXX do something with the conditions.
        return self.conditions

b = Book('book')
print(b.price(">4.00").author('J. K. Rowling').execute())