如何将文件行从文件追加到两个特定行之间的列表中？

Question

If I have a text file of the following:

Watermelon
Carrot
Spinach
Lettuce
Tomato
Lemon

How would I append the lines from Carrot to Tomato (inclusive) into an empty list?

mylist = ['Carrot','Spinach','Lettuce','Tomato']

I've tried:

mylist = []
for aline in file:
    aline = aline.rstrip('\n')
if aline.startswith('Carrot')
    mylist.append(aline)

Which obviously just appends 'Carrot' to the list but how can I make it keep appending till the stop point?

Answer 1

You can try this:

with open('filename.txt') as f:

   file_data = [i.strip('\n') for i in f][1:-1]

A more generic solution:

with open('filename.txt') as f:
    s = [i.strip('\n') for i in f]
    final_data = s[s.index("Carrot"):s.index("Tomato")+1] if s.index("Carrot") < s.index("Tomato") else s[s.index("Tomato"):s.index("Carrot")+1]

Answer 2

In a more generic way, assuming that both the location of "Carrot" and "Tomato" is not fixed, but "Carrot" will always come before "Tomato", you can do something like this:

with open('file.txt') as temp_file:
  lines = [line.rstrip() for line in temp_file]

lines[lines.index("Carrot"):lines.index("Tomato")+1]  

In case you could not tell which value comes first (Tomato or Carrot), you can let Python figure it out for you:

with open('file.txt') as temp_file:
  lines = [line.rstrip() for line in temp_file]

carrot_idx = lines.index("Carrot")
tomato_idx = lines.index("Tomato")

lines[min(carrot_idx,tomato_idx):max(carrot_idx,tomato_idx)+1]  

Answer 3

takewhile and dropwhlie from itertools are made for that.

from itertools import takewhile, dropwhile

def from_to(filename, start, end):
    with open(filename) as f:
        stripped = (line.rstrip() for line in f)
        dropped = dropwhile(lambda line: line != start, stripped)
        taken = takewhile(lambda line: line != end, dropped)
        for item in taken:
            yield item
        yield end

Demo with your file:

>>> list(from_to('test.txt', 'Carrot', 'Tomato'))
['Carrot', 'Spinach', 'Lettuce', 'Tomato']

This approach has the advantage that you don't give up the iterator properties of an opened file, so there will be no memoery problems with very large files.