Question

Exercise:

There’s too much repetition in this file. Use strings, formats, and escapes to print out line1, line2, and line3 with just one target.write() command instead of 6.

Code from the book:

from sys import argv

script, filename = argv

print "We're going to erase %r." % filename
print "If you don't want that, hit CTRL-C (^C)."
print "If you do want that, hit RETURN."

raw_input("?")

print "Opening the file..."
target = open(filename, 'w')

print "Truncating the file.  Goodbye!"
target.truncate()

print "Now I'm going to ask you for three lines."

line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")

print "I'm going to write these to the file."

target.write(line1)
target.write("\n")
target.write(line2)
target.write("\n")
target.write(line3)
target.write("\n")

print "And finally, we close it."
target.close()

My code:

from sys import argv

script, filename = argv

print "We're going to erase %r." % filename
print "If you don't want that, hit CTRL-C (^C)."
print "If you do want that, hit RETURN."

raw_input("?")

print "Opening the file..."
target = open(filename, 'w')

print "Truncating the file.  Goodbye!"
target.truncate()

print "Now I'm going to ask you for three lines."

line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")

print "I'm going to write these to the file."

target.write("%s\n%s\n%s\n") %(line1,line2,line3)


print "And finally, we close it."
target.close()

My solution doesn’t work. I searched with Google to see if I can solve this exercise with the things I find there but I haven’t managed to come out with the correct code.
What is the solution to this exercise?

Answer 1

What you’re doing right now is applying the % formatting operator to the result of the expression

target.write("%s\n,%s\n,%s\n")

What you want to do is apply the % operator to the string

"%s\n%s\n%s\n"  // Note that the code from the book doesn't print commas

and then pass the result of that to target.write().