Python:: Easy lab

Python tidbits for CSE 5120 March Programming Assignment

Kerstin Voigt, March 2021

Work in Python Shell to test out code snippets

Program loaded

dtab a copy of list DATATABLE

DATATABLE is a list of Python dictionaries

Each line a dictionary that lists KEY : VALUE pairs

Let’s all each line an INSTANCE

The third instance of datatable dtab

Iterating over all ATTRIBUTES of the instance, Here: just to print

Iterating over all VALUES of the instance, Here: just to print

Iterating over all ITEMS (key:val) of the instance …

A Python dictionary is equivalent to a C++ Map data structure;

Use [ ] operator on key to obtain value associated with key

A RULE is represented by plain LIST of attributes; all attribs are are to have value 1 in an instance in order for rule to “cover” the instance (= rule is applicable to instance)

This function definition should go into your .py file …. But for quick prototyping, you CAN define a quick fct within the Pyton shell … benefit of interpreter!

Again: put fct def into .py file; in defined in shell just for demo

DEC is global; here DEC = ‘ok’

Neither of these 4 rules covers any neg instance, i.e., inst wit ‘ok’ : 0

These 2 rules cover one or more neg instances

… find them in listing here …

Empty rule [ ] covers all instances be default; thus True

Left to define …

def num_covers(dtab, rule):

… your code …

• Identifies and counts all instances in dtab that are covered by the rule

• Special case: if rule is empty, return the length of dtab bec “all” instances are coverd by rule [ ]

def num_covers_pos(dtab, rule):

… your code …

• Identifies and counts all POSITIVE instances (those with ‘ok’:1) that are covered by the rule

• Special case: if rule is empty, return the number of all positive instances in dtab; they are all covered by rule [ ]