python 3 print with extra characters

Question

I have the following section to print the ant build info into a file.

rsltFile = open('buildLog.txt', 'w')
    p = subprocess.Popen('call ant compile', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    for line in p.stdout.readlines(): 
        rsltFile.write("%s\n" % line) 
        print(line)
    retval = p.wait()

It worked fine in python 2.6 but it print out some extra character for each line in python 3.2, like this following:

b'Buildfile: C:\\workspace\\VCT2400_Service\\ServiceApplication\\build.xml\r\n'
b'\r\n'
b'init:\r\n'
b'\r\n'
b'clean:\r\n'
b'    [mkdir] Created dir: C:\\workspace\\VCT2400_Service\\ServiceApplication\\classes\r\n'
b'\r\n'
b'compile:\r\n'
b'    [javac] Compiling 492 source files to C:\\workspace\\VCT2400_Service\\ServiceApplication\\classes\r\n'

Those b' and \r\n' are extra, not expect them there.

Answer 1

Files opened in text mode expect strings to be written into them. You get byte objects from readlines() which are converted to string representation by format % operator.

Open the file in binary mode and dump lines there directly:

rsltFile = open('buildLog.txt', 'wb')
...
rsltFile.write(line + b'\n')

...or, interpret subprocess output as a string:

linestr = line.decode('utf8')

P.S. It looks like adding '\n' is not needed, each line already ends with a newline.