Title: easy file parsing
Submitter: Michael Haimes (other recipes)
Last Updated: 2006/09/18
Version no: 1.2
Category: Files

Description:

This is useful for making easy and human to write definition files for whatever use. For example, lets say you are writing a simulator and you need an easy, human way to define parts about a given world like light sources, obstacles, and dimensions. see the discussion for this example fleshed out in code.

Source: Text Source

#parse a python file in a given environment, and get out some results
from os import dirname

def parseFile(filename, envin, envout = {}):
	exec "from sys import path" in envin
	exec "path.append(\"" + dirname(filename) + "\")" in envin
	envin.pop("path")
	lines = open(filename, 'r').read()
	exec lines in envin
	returndict = {}
	for key in envout:
		returndict[key] = envin[key]
	return returndict

Discussion:

For the example above, You might write something like the following:

from parsefile import parseFile

class World:

def dimensions(self, width, height):
self.width = width
self.height = height

def __init__(self, filename):
self.lightsources = []
self.obstacles = []
envin = {}
envin['dimensions'] = self.dimensions
envin['newobstacle'] = lambda x,y: self.obstacles.append((x,y))
envin['newlightsource'] = lambda x,y: self.lightsources.append((x,y))
parseFile(filename, envin)


If you were to then call something like World(file) in the runtime of your program where file is as follows:
####################
dimensions(4, 5)
newlightsource(1, 2)
newlightsource(2, 3)
newobstacle(0, 1)
####################

You will end up with an instance of class World with the appropriate data, thus it is simple to create new ways to specify data for your program