[Using Context Managers for File I/O] #python #python3

input.txt

Line 1
Line 2
Line 3

with_context_manager.py

import sys

class myFileReader(object):
	
	def __init__(self, filename):
		print("in __init__", file=sys.stderr)
		self.f = open(filename)

	def __enter__(self):
		print("in __enter__", file=sys.stderr)
		return self

	def readlines(self):
		for line in self.f.readlines():
			yield line

	def __exit__(self,exc_type, exc_value, traceback):
		print("in __exit__", file=sys.stderr)
		
if __name__ == "__main__":
	
	# Demonstration of Context Managers for file reading
	#See: https://docs.python.org/3/reference/datamodel.html#with-statement-context-managers	
	#See: https://www.python.org/dev/peps/pep-0343/
	with myFileReader("input.txt") as mfr:
		for line in mfr.readlines():
			print("readline:", line)