如何在Python中读取txt文件的特定部分？

Question

I need to extract a portion of text from a txt file.
The file looks like this:

STARTINGWORKIN DD / MM / YYYY HH: MM: SS
... text lines ...
... more text lines ...
STARTINGWORKING DD / MM / YYYY HH: MM: SS
... text lines I want ...
... more text lines that I want ...

• The file starts with STARTINGWORK and ends in text lines.
  I need to extract the final text portion after the last STARTINGWORK, without the STARTINGWORK str

I tried use 3 for loops (one to start, another read the between line, and the last to end)

     file = "records.txt"
     if file.endswith (".txt"):
       if os.path.exists (file):
         lines = [line.rstrip ('\ n') for line in open (file)]
         for line in lines:
             #extract the portion

Answer 1

Try this:

file = "records.txt"
extracted_text = ""
    if file.endswith (".txt"):
        if os.path.exists (file):
            lines = open(file).read().split("STARTINGWORKING")
            extracted_text = lines[-1] #Here it is

Answer 2

You can use file_read_backwards module to read file from end to beginning. It helps you save time if the file size is big:

from file_read_backwards import FileReadBackwards

with FileReadBackwards("records.txt") as file:
    portion = list()
    for line in file:
         if not line.startswith('STARTINGWORKING'):
            portion.append(line)
         else:
            break
portion.reverse()

portion contains lines desired.

Answer 3

I would take the regex path to tackle this:

>>> import re
>>> input_data = open('path/file').read()
>>> result = re.search(r'.*STARTINGWORKING\s*(.*)$', input_data, re.DOTALL)
>>> print(result.group(1))
#'DD / MM / YYYY HH: MM: SS\n... text lines I want ...\n... more text lines that I want ...'

Answer 4

The get_final_lines generator tries to avoid malloc ing more storage than necessary, while reading a potentially large file.

def get_final_lines(fin):
    buf = []
    for line in fin:
        if line.startswith('STARTINGWORK'):
            buf = []
        else:
            buf.append(line)

    yield from buf


if __name__ == '__main__':
    with open('some_file.txt') as fin:
        for line in get_final_lines(fin):
            print(line.rstrip())

Answer 5

You can have a variable that saves all the lines you have read since the last STARTINGWORK .
When you finish processing the file you have just what you need.

Certainly you do not need to read all the lines to a list first. You can read it directly in the open file and that returns one line at a time. ie:

result = []
with open(file) as f:
    for line in f:
        if line.startswith("STARTINGWORK"):
            result = []       # Delete what would have accumulated
        result.append(line)  # Add the last line read
print("".join(result))

In the result you have everything after the last STARTINGWORK, inclusive you can keep the result [1:] if you want to delete the initial STARTINGWORK

- Then in the code:

#list
result = []

#function
def appendlines(line, result, word):
  if linea.startswith(word):
    del result[:]
  result.append(line)
  return line, result

with open(file, "r") as lines: 
  for line in lines:              
    appendlines(line, result, "STARTINGWORK")
new_result = [line.rstrip("\n") for line in result[1:]]