In many cases we need to read from or write to a file. Python has simple mechanisms that we can use for that purpose.

Delete file and create new one with initiall text

def prepareOutputFile():	
	with open(outputFile, "w") as myfile:
		myfile.write( "UserID,BusinessID\n" )
   	return

Append text to a file

def writeOutput( string ):
	with open(outputFile, "a") as myfile:
		myfile.write( string )
    	return

Open file and process line by line:

with open(inputFile) as f:
	next(f) # skip header
	for line in f:
		print line

Stripping the newline character:

read a file line by line into a list

usersList = [line.rstrip('\n') for line in open(inputUsersFile)]