12. File I/O¶

12.1 Open¶

Files are opened using the open() function.

def main():
    f = open('lines.txt')
    for line in f:
        print(line.rstrip())

The open function returns a file object. This object is an iterator, so a for loop can be used to get it one line at a time without having to buffer the entire file in memory.
rstrip strips any white space and line endings.
By default, it’s in read-only mode. Same as f = open('lines.txt'. 'r').
For write mode, f = open('lines.txt', 'w').
For read and write, f = open('lines.txt'. 'r+')

12.2 Newline¶

specified using \n.

12.3 Write text¶

To write, use print and write to file

def main():
    infile = open('lines.txt', 'rt')
    outfile = open('lines-copy.txt', 'wt')
    for line in infile:
        print(line.rstrip(), file=outfile)
        print('.', end='', flush=True)
    outfile.close()
    print('\ndone.')

rt opens in read and text mode (which is also the default).
Good idea to close the outfile explicitly
An alternative to print is to use outfile.writelines(line).

12.4 Write binary¶

def main():
    infile = open('berlin.jpg', 'rb')
    outfile = open('berlin-copy.jpg', 'wb')
    while True:
        buf = infile.read(10240)
        if buf:
            outfile.write(buf)
            print('.', end='', flush=True)
        else: 
            break
    outfile.close()
    print('\ndone.')

rb opens in read and binary mode.
This file (image) can’t be opened in text mode.

11. String Objects 13. Built-in Functions