Python 3 Web Development Beginner's Guide

Time for action creating instances

The next method we look at is the constructor the __init__() method. It will be used to create individual instances of an entity. The constructor can be called in two ways:

• With a single id argument, in which case, an existing record will be retrieved from the database and the instance initialized with the column values of this record, or
• With a number of keyword arguments to create a new instance and save this as a new database record

The code to implement this behavior looks like the following:

Chapter5/entity.py

def __init__(self,id=None,**kw):
		for k in kw:
			if not k in self.__class__.columns :
				raise KeyError("unknown column") cursor=self.threadlocal.connection.cursor() if id: if len(kw): raise KeyError("columns ...