The following code segment is supposed to read all of the lines from test.txt and save them in copy.txt.
infile = open("test.txt", "r")
outfile = open("copy.txt", "w")
line = infile.readline()
____________________
outfile.write(line)
line = infile.readline()
infile.close()
outfile.close()
Which line of code should be placed in the blank to achieve this goal?

Question

The following code segment is supposed to read all of the lines from test.txt and save them in copy.txt.
infile = open("test.txt", "r")
outfile = open("copy.txt", "w")
line = infile.readline()
____________________
   outfile.write(line)
   line = infile.readline()
infile.close()
outfile.close()
Which line of code should be placed in the blank to achieve this goal?

BlackTom AI · Accepted Answer

We need to determine which line properly completes the loop to read all lines from test.txt and write them to copy.txt.
Option 1: while line != "
" : This would stop when the line is just a newline character. If a line contains actual content, including the trailing newline, this condition remains true, but many lines end with a newline and not with a solitary newline string; also the last line may not end with a newline, causing inconsistent behavior. This choice could prematurely terminate or miss lines depending on file content.
Option 2: while line == "
" : This condition would continue only while the current line is exactly a single newline character. Since that rarely matches for regular text lines (which usually end with a newline, but not equal to a single newline string in this context), the loop would either do nothing or loop incorrectly, leading to improper copying of the file.
Option 3: while line != "" : This condition checks for the end of the file, where readline returns an empty string when there are no more lines. As long as a line is not the end-of-file marker (an empty string), the body will execute, writing the line to the output and then reading the next line. This is a standard pattern for reading a file line by line until EOF.
Option 4: while line == "" : This would loop only while the current line is an empty string, which would typically be true only if there is a blank line at the very start. In most normal text files, this would either do nothing or skip valid content, failing to process the file correctly.
Across the options, the key concept is how file-reading loops detect end-of-file with readline. The typical and reliable approach is to continue looping while there is content present, i.e., while line != "". This ensures every line is written until the end of file is reached, including the final line whether or not it ends with a newline character.

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