[Python] #7 Python File I/O

This is a self note while taking the online course from: LinkedIn Learning: Learning Python by Joe Marini LinkedIn Learning: Python Essential Training by Bill Weinman

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1. Open files

• open function returns a file object which is an iterator
• write mode(w) empties the file and write over
• ‘b’ - open as binary file (default is text file)

f = open('line.txt', 'r')
    for line in f:
        print(line.rstrip())

(Result, line.txt)

1st line
2nd line
3rd line
4th line
5th line

2. Write text file

• can use print(str, file=fileName) fucntion to write into files
• flush output buffer for accuracy

infile = open('line.txt', 'rt')

# new file object for output file (write-text mode)
outfile = open('line-copy.txt', 'wt')

# read and write each line in input file to output file
for line in infile:
    print(line.rstrip(), file=outfile) # strip from the end of string
    print('.', end='', flush=True)  # flush=True flushes the output buffer
outfile.close()     # buffering -> prevent data loss
print('\ndone.')

(Result)

.....
done.

(line-copy.txt)

1st line
2nd line
3rd line
4th line
5th line

3. Write(Copy) binary file

• code below copies a jpg file with write-binary mode:

# open jpg file in binary file
infile = open('uw_madison.jpeg', 'rb')
outfile = open('uw-copy.jpeg', 'wb')
while True:
    buf = infile.read(10240)    # use 10KB = 10240 as the buffer
    if buf:
        outfile.write(buf)
        print('.', end='', flush=True)
    else:
        break
outfile.close()
print('\nDone.')