Python のファイル操作

# "w" creates the file (or empties it) and opens it for writing.
with open("notes.txt", "w") as file:
    file.write("first line\n")
    file.write("second line\n")

# "a" appends to the end of an existing file.
with open("notes.txt", "a") as file:
    file.write("third line\n")

# "r" (the default) reads. read() returns the whole file as one string.
with open("notes.txt") as file:
    print(file.read())

# Loop over a file to read it line by line.
with open("notes.txt") as file:
    for number, line in enumerate(file, start=1):
        print(number, line.strip())

# "with" closes the file automatically, even if an error happens.