ex16.py

# files commands

from sys import argv

script, filename = argv

print("We're going to erase %r." % filename)
print("If you don't want that, hit CTRL-C (^C).")
print("If you do want that, hit RETURN.")

input("?")

print("Opening the file...")
target = open(filename, 'w')

print("Truncating the file.  Goodbye!")
target.truncate()

print("Now I'm going to ask you for three lines.")

line1 = input("line 1: ")
line2 = input("line 2: ")
line3 = input("line 3: ")

print("I'm going to write these to the file.")

target.write(line1 + "\n" + line2 + "\n" + line3 + "\n")

print("And finally, we close it.")
target.close()

# 'r'	Open a file for reading. (default)
# 'w'	Open a file for writing. Creates a new file if it does not exist or truncates the file if it exists.
# 'x'	Open a file for exclusive creation. If the file already exists, the operation fails.
# 'a'	Open for appending at the end of the file without truncating it. Creates a new file if it does not exist.
# 't'	Open in text mode. (default)
# 'b'	Open in binary mode.
# '+'	Open a file for updating (reading and writing)

# instead of closing and opening and assigning the file  and target variable so many times , we could have
# used + mode, which allows multiple editing