在Python中删除找到某些字符的文本文件的前两行

Question

I have a text file that is an ebook. Sometimes full sentences are broken up by two new lines, and I am trying to get rid of these extra new lines so the sentences are not separated mid-sentence by the new lines. The file looks like

Here is a regular sentence.
This one is fine too.
However, this

sentence got split up.

If I hit delete twice on the keyboard, it'd fix it. Here's what I have so far:

with open("i.txt","r") as input:
    with open("o.txt","w") as output: 
        for line in input:
            line = line.strip()

            if line[0].isalpha() == True and line[0].isupper() == False:  
                # something like hitting delete twice on the keyboard
                output.write(line + "\n")
            else:
                output.write(line + "\n")

Any help would be greatly appreciated!

Answer 1

If you can read the entire file into memory, then a simple regex will do the trick - it says, replace a sequence of new lines preceding a lowercase letter, with a single space:

import re

i = open('i.txt').read()
o = re.sub(r'\n+(?=[a-z])', ' ', i)

open('o.txt', 'w').write(o)

Answer 2

The important difference here is that you are not in an editor, but rather writing out lines, that means you can't 'go back' to delete things, but rather recognise they are wrong before you write them.

In this case, you will iterate five times. Each time you will get a string ending in \\n to indicate a newline, and in two of those cases, you want to remove that newline. The easiest way I can see to identify that time is if there was no full stop at the end of the line. If we check that, and strip the newline off in that case, we can get the result you want:

with open("i.txt", "r") as input, open("o.txt", "w") as output:
    for line in input:
        if line.endswith(".\n"):
            output.write(line)
        else:
            output.write(line.rstrip("\n"))

Obviously, sometimes it will not be possible to tell in advance that you need to make a change. In such cases, you will either need to make two iterations over the file - the first to find where you want to make changes, the second to make them, or, alternatively, store (part of, or all of) the file in memory until you know what you need to change. Note that if your files are extremely large, storinbg them in memory could cause problems.

Answer 3

You can use fileinput if you just want to remove the lines in the original file:

from __future__ import print_function

for line in fileinput.input(""i.txt", inplace=True):
    if not line.rstrip().endswith("."):
         print(line.rstrip(),end=" ")
    else:
        print(line, end="")

Output:

Here is a regular sentence.
This one is fine too.
However, this sentence got split up.