'''
File: callback_demo2.py
To demonstrate implementation and use of callbacks in Python,
using classes with methods as the callbacks.
Author: Vasudev Ram
Copyright 2017 Vasudev Ram
Web site: https://vasudevram.github.io
Blog: https://jugad2.blogspot.com
Product store: https://gumroad.com/vasudevram
'''
from __future__ import print_function
import sys
from time import sleep
class FileReporter(object):
def __init__(self, filename):
self._filename = filename
try:
self._fil = open(self._filename, "w")
except IOError as ioe:
sys.stderr.write("While opening {}, caught IOError: {}\n".format(
self._filename, repr(ioe)))
sys.exit(1)
def report(self, message):
self._fil.write(message)
class ScreenReporter(object):
def __init__(self, dest):
self._dest = dest
def report(self, message):
self._dest.write(message)
def square(i):
return i * i
def cube(i):
return i * i * i
def processor(process, times, report_interval, reporter):
result = 0
for i in range(1, times + 1):
result += process(i)
sleep(0.1)
if i % report_interval == 0:
# This is the call to the callback method
# that was passed to this function.
reporter.report("Items processed: {}. Running result: {}.\n".format(i, result))
file_reporter = FileReporter("processor_report.txt")
processor(square, 20, 5, file_reporter)
stdout_reporter = ScreenReporter(sys.stdout)
processor(square, 20, 5, stdout_reporter)
stderr_reporter = ScreenReporter(sys.stderr)
processor(square, 20, 5, stderr_reporter)
