如何制作程序，以便用户可以指定文件名？

Question

I initially wrote a program that would read a file containing text, then would read each line and send it to the output file. Now I am trying to make it so that I can allow the user to specify the file name on the command line and if the user doesn't specify a name, prompt them for one. Any Idea how to do this?

#Allow the user to enter the input and output file names
inputFileName = input("Input file name: ")
outputFileName = input("Output file name: ")

#Open the input and output files
infile = open(inputFileName,"r")
outfile = open(outputFileName, "w")

#Define count
count=0

#Reads the input file and produces the output file
line = infile.readline()
while line != "":
count = count+1
print(count, line)
line = infile.readline()

#Close the infile and the outfile    
infile.close()
outfile.close()

Answer 1

Use argparse

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--file', help='file path') #add --file to the args
args = parser.parse_args()

if not(args.file): #if they didn't specify a --file, prompt them
    file = input("Please enter file path?")
else:
    file = args.file #if they did specify file, make file what they specified in the cmd

print(file)

Then you call it with python program.py --file doc.txt

Edited for your specific case

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--input', help="input file")
parser.add_argument('--output', help="output file")
args = parser.parse_args()

if args.input:
    inputFileName = args.input
else:
    inputFileName = input("Input file name: ")

if args.output:
    outputFileName = args.output
else:
    outputFileName = input("Output file name: ")


#Open the input and output files
infile = open(inputFileName,"r")
outfile = open(outputFileName, "w")

#Define count
count=0

#Reads the input file and produces the output file
line = infile.readline()


while line != "":
    count = count+1
    print(count, line)
    line = infile.readline()

#Close the infile and the outfile    
infile.close()
outfile.close()

Suggested Edit

The way you are reading each line is really strange, I would suggest something like this

for line in infile: #loop through every line in infile
    outfile.write(line) #write this line to outfile
    print(line.rstrip("\n")) #print this line, but don't print the \n. that's why you were having multiple line breaks before

Answer 2

If you want to be able to call something like this:

python program_name outputFileName

then

from sys import argv
try:
    outputFileName = argv[1]
except IndexError:
    outputFileName = input("Output file name: ")

Also, I'm not sure if this was intentional, but your code doesn't actually write anything to outfile.