Very basic Python question (strings, formats and escapes)

Question

I am starting to learn Python with an online guide, and I just did an exercise that required me to write this script:

from sys import argv

script, filename = ar         


        

Answer 1

How about this? I used a for loop.

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 want that, hit RETURN.")

input("?")

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

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

print("Now I am going to ask you for three lines.")

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

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

for a in (line1, line2, line3):
    target.write("\n")

target.close()

Answer 2

The guide is suggesting creating a single string and writing it out rather than callingwrite() six time which seems like good advice.

You've got three options.

You could concatentate the strings together like this:

line1 + "\n" + line2 + "\n" + line3 + "\n"

or like this:

"\n".join(line1,line2,line3) + "\n"

You could use old string formatting to do it:

"%s\n%s\n%s\n" % (line1,line2,line3)

Finally, you could use the newer string formatting used in Python 3 and also available from Python 2.6:

"{0}\n{1}\n{2}\n".format(line1,line2,line3)

I'd recommend using the last method because it's the most powerful when you get the hang of it, which will give you:

target.write("{0}\n{1}\n{2}\n".format(line1,line2,line3))

Answer 3

I think they want you to use string concatenation:

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

Much less readable, but you have only one target.write() command

Answer 4

bad

Original code is repetitive, and copy-pasting code is dangerous ( Why is "copy and paste" of code dangerous? ):

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")

good

Much shorter, can change it to 4+ lines just by changing one character:

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

lines = [raw_input("line {i}: ".format(i=i)) for i in range(1,4)]

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

for line in lines:
    target.write(line+'\n')