Question

I want to create a text file and add data to it, line by line. If a data line already exists in the file, it should be ignored. Otherwise, it should be appended to the file.

Answer 1

I did it like this,

def retrieveFileData():
    """Retrieve Location/Upstream data from files"""
    lines = set()
    for line in open(LOCATION_FILE):
        lines.add(line.strip())
    return lines

def add_line(line):
    """Add new entry to file"""
    f = open(LOCATION_FILE, 'a')
    lines = retrieveFileData()
    print lines
    if line not in lines:
        f.write(line + '\n')
        lines.add(line)
        f.close()
    else:
        print "entry already exists"

if __name__ == "__main__":
    while True:
        line = raw_input("Enter line manually: ")
        add_line(line)
        if line == 'quit':
            break