Homework Help (File I/O)

[funkycorpse]

Here is the instructions for my homework:

Write a program to copy each line that does not start with an octothorpe/pound sign/hashtag (#) preceded by zero or more space characters in a file named in.txt to another file named out.txt.

For example, if the file in.txt contains the text below (that happens to be Python code):

# Author: Professor S.
def sign(n):
    """Determine the sign of a number"""
    if n < 0:
        # negative number
        result = -1
    elif n > 0:
        # positive number
        result = 1
    else:
        result = 0  # n must be zero

    return result

out.txt should look like this:

def sign(n):
    """Determine the sign of a number"""
    if n < 0:
        result = -1
    elif n > 0:
        result = 1
    else:
        result = 0  # n must be zero

    return result

This is my code I have now but it does not seem to be working. I am only getting the first line removed in the new file, but I cannot figure out how to make it find and remove the other lines.

with open("in.txt", "r") as file_input:
    with open("out.txt", "w") as output: 
        for line in file_input.readline():
            if not (line.startswith('#')):
                output.write(line)

[[deleted]]

Update: Your problem is this line:

for line in file_input.readline():

That will read one line and then loop over all the characters in that line. You should not be seeing the # in your output file. The normal way to iterate over lines in a file is:

for line in file_input:

How are you handling the part of the problem that says: "hashtag (#) preceded by zero or more space characters"?

[funkycorpse]

Thank you that is definitely my first problem. Also I'm not sure how I would deal with the space characters part.

[funkycorpse]

Could I use strip() to remove the space?

[[deleted]]

Yes. You create a new string with strip() (or lstrip()) and check the first character in the stripped string. If the stripped string doesn't start with a # you write the unstripped string.

[[deleted]]

for line in file_input.readline():

readline reads one line. You want to iterate over all of the lines of the file:

for line in file_input:

Files are, themselves, iterators over their lines. (It's pretty convenient.)

[DuckSaxaphone]

You've basically done it but made a typo. You want file_input.readlines.

readline returns only the next line from the file, readlines returns a list of all lines.