[FIXED] porting Python 2 program to Python 3, random line generator

Issue

I have a random line generator program written in Python2, but I need to port it to Python3. You give the program the option -n [number] and a file argument to tell it to randomly output [number] number of lines from the file. Here is the source for the program:

#!/usr/bin/python

import random, sys
from optparse import OptionParser

class randline:
    def __init__(self, filename):
        f = open(filename, 'r')
        self.lines = f.readlines()
        f.close()

    def chooseline(self):
        return random.choice(self.lines)

def main():
    version_msg = "%prog 2.0"
    usage_msg = """%prog [OPTION]... [FILE] [FILE]...

Output randomly selected lines from each FILE."""

    parser = OptionParser(version=version_msg,
                          usage=usage_msg)
    parser.add_option("-n", "--numlines",
                      action="store", dest="numlines", default=1,
                      help="output NUMLINES lines (default 1)")
    options, args = parser.parse_args(sys.argv[1:])

    try:
        numlines = int(options.numlines)
    except:
        parser.error("invalid NUMLINES: {0}".
                     format(options.numlines))
    if numlines < 0:
        parser.error("negative count: {0}".
                     format(numlines))
    if len(args) < 1:
        parser.error("input at least one operand!")

    for index in range(len(args)):
        input_file = args[index]
        try:
            generator = randline(input_file)
            for index in range(numlines):
                sys.stdout.write(generator.chooseline())
        except IOError as (errno, strerror):
            parser.error("I/O error({0}): {1}".
                        format(errno, strerror))

if __name__ == "__main__":
    main()

When I run this with python3:

python3 randline.py -n 1 file.txt

I get the following error:

  File "randline.py", line 66
    except IOError as (errno, strerror):
                      ^
SyntaxError: invalid syntax

Can you tell me what this error means and how to fix it?

Thanks!

Solution

This line is incorrect syntax:

except IOError as (errno, strerror):

The correct form is:

except IOError as err:

then you can examine err for attributes like errno, etc.

I'm not sure where you got the original line from, it isn't valid Python 2.x syntax either.

Answered By - Ned Batchelder