How do I combine lines in a text file in a specific order?

Question

I'm trying to transform the text in a file according the following rule: for each line, if the line does not begin with "https", add that word to the beginning of subsequent lines until you hit another line with a non-https word.

For example, given this file:

Fruit
https://www.apple.com//
https://www.banana.com//
Vegetable
https://www.cucumber.com//
https://www.lettuce.com//

I want

Fruit-https://www.apple.com//
Fruit-https://www.banana.com//
Vegetable-https://www.cucumber.com//
Vegetable-https://www.lettuce.com//

Here is my attempt:

one = open("links.txt", "r")
for two in one.readlines():

    if "https" not in two:
        sitex = two
        
    else:
        print (sitex + "-" +two)

Here is the output of that program, using the above sample input file:

Fruit
-https://www.apple.com//

Fruit
-https://www.banana.com//       

Vegetable
-https://www.cucumber.com//     

Vegetable
-https://www.lettuce.com//   

What is wrong with my code?

Answer 1

To fix that we need to implement rstrip() method to sitex to remove the new line character at the end of the string. (credit to BrokenBenchmark )

second, the print command by default newlines everytime it's called, so we must add the end="" parameter to fix this.

So your code should look like this

one = open("links.txt", "r")
for two in one.readlines():
    if "https" not in two:
        sitex = two.rstrip()
    else:
        print (sitex + "-" +two,end="")
one.close()

Also always close the file when you are done.

Answer 2

Lines in your file end on "\n" - the newline character.

You can remove whitespaces (includes "\n" ) from a string using strip() (both ends) or rstrip() / lstrip() (remove at one end).

print() adds a "\n" at its end by default, you can omit this using

print("something", end=" ")
print("more)   # ==> 'something more' in one line

Fix for your code:

# use a context handler for better file handling
with open("data.txt","w") as f:
    f.write("""Fruit
https://www.apple.com//
https://www.banana.com//
Vegetable
https://www.cucumber.com//
https://www.lettuce.com//
""")


with open("data.txt") as f:
    what = ""
    # iterate file line by line instead of reading all at once
    for line in f:
        # remove whitespace from current line, including \n
        # front AND back - you could use rstring here as well
        line = line.strip() 
        # only do something for non-empty lines (your file does not
        # contain empty lines, but the last line may be empty
        if line:
            # easier to understand condition without negation
            if line.startswith("http"):
                # printing adds a \n at the end
                print(f"{what}-{line}") # line & what are stripped
            else:
                what = line

Output:

Fruit-https://www.apple.com//
Fruit-https://www.banana.com//
Vegetable-https://www.cucumber.com//
Vegetable-https://www.lettuce.com//

See:

• str.lstrip( [chars] )
• str.rstrip( [chars] )
• str.strip( [chars] )

[chars] are optional - if not given, whitespaces are removed.

Answer 3

You need to strip the trailing newline from the line if it doesn't contain 'https' :

sitex = two

should be

sitex = two.rstrip()

---

You need to do something similar for the else block as well, as ShadowRanger points out:

print (sitex + "-" +two)

should be

print (sitex + "-" + two.rstrip())