用Python复制文件的这种方法有什么问题？

Question

I don't understand why my new file has a bunch of special characters in it that were not in the original file. This is similar to ex17 in Learn Python The Hard Way .

#How to copy data from one file into another

from sys import argv
from os.path import exists

script, from_file, to_file = argv

print "Copying from %s to %s" % (from_file, to_file)

from_data = open(from_file, "r").read()

print "The input file is %d bytes long" % len(from_data)

print "Checking if output file exist..... %r" % exists(to_file)
print "Hit return to continue or Cntl C to quit"

#keyboard input
raw_input()

out_file = open(to_file, "r+")
out_file.write(from_data)

print "Okay all done, your new file now contains:"
print out_file.read()

out_file.close()

Answer 1

You must open the files in binary mode ( "rb" and "wb" ) when copying.

Also, it's in general better to just use shutil.copyfile() and not re-invent this particular wheel. Copying files well can be complex (I speak with at least some authority ).

Answer 2

Try rewinding the file pointer back to the beginning using seek before you read the results.

out_file = open(to_file, "r+")
out_file.write(from_data)

print "Okay all done, your new file now contains:"
out_file.seek(0)
print out_file.read()