如何在 Python 中打印文本文件每个段落的第一行？

Question

Let's say I have a text file like this:

Tom
15
Basketball

James
16
Tennis
Track
Choir

Tim
14
Band
Class Chairman

I would like to display this:

Tom
James
Tim

My program allows the user to append more information into the txt file. While I could make it such that it only reads line 1, 5 and 11, the problems lies with displaying any added information. Each paragraph might also have different amount of lines. From what I know (and find online), there isn't a way to print only the first line of each paragraph of a txt file without importing external tools. Is there a convoluted way to do this or is there a different approach to solve this?

Answer 1

f = open('filename.txt', 'rt')

for entry in f.read().split('\n\n'):
    print(entry[0 : entry.index('\n')])

filename.txt is the name of that text file, rt is the file opening mode: r stands for 'read' (read-only mode) and t for 'text' file.

Every entry (paragraph) is separated by two newlines (think about it) so we .split() by that and for every such entry, we know that the first line is the name, so we splice the string as [0 : entry.index('\\n')] as entry.index('\\n') gives the index just next to the first newline in the entry.

Also, make sure the file does exist there before running it, otherwise it'll throw an error.

Answer 2

Use a variable to keep track of whether the line on the previous iteration contained any text or not. You want the lines which have text, and where the previous line (if any) did not have any text.

previous_has_text = False
with open('input.txt') as f:
    for line in f:
        line = line.strip()
        if line:
            # THIS line has text
            if not previous_has_text:
                print(line)
            previous_has_text = True  # ready for next iteration
        else:
            previous_has_text = False  # likewise

Gives:

Tom
James
Tim

With this method, it does not matter if there is more than one blank line between paragraphs. Also if the "blank" line contains a space it will still work.