python - How to write to CSV and not overwrite past text

Question

The code below is what I have so far. When it writes to the .csv it overwrites what I had previously written in the file.How can I write to the file in such a way that it doesn't erase my previous text.(The objective of my code is to have a person enter their name and have the program remember them)

def main(src):
    try:
        input_file = open(src, "r")
    except IOError as error:
        print("Error: Cannot open '" + src + "' for processing.")
    print("Welcome to Learner!")
    print("What is your name? ")
    name = input()
    for line in input_file:
        w = line.split(",")
        for x in w:    
            if x.lower() == name.lower():
                print("I remember you "+ name.upper())
            else:
                print("NO")
                a = open("learner.csv", "w")
                a.write(name)
                a.close()
                break
if __name__ == "__main__":
    main("learner.csv")

Answer 1

You need to append to file the next time. This can be done by opening the file in append mode.

def addToFile(file, what):
    f = open(file, 'a').write(what)