Python: Modifying text file after certain character

Question

I'm doing some operations on a text file with python. But there is one thing I couldn't find a solution yet. I hope someone here can help me.

In that text file in every line I have the word order and afterwards a various string consisting of , and numbers.

Now I want to delete the word order and everything that follows in that line, but I can't find out how. The location in the file where order is stated always varies, so I cannot point to a certain location and delete everything afterwards.

Answer 1

It's extremly easy to do what you want because you only DELETE parts of the text, so you can rewrite in the same file that you read by using the 'r+' mode.

with open(filename,'r+') as fr,open(filename,'r+') as fw:
    for line in fr:
        x = line.find('order')
        fw.write(line if x==-1
                 else line[0:x]+'\n' if '\n' in line
                 else line[0:x])
    fw.truncate()

If your file isn't too big, so can be entirely read and hold in the RAM, here's another method using a regex:

import re

r = re.compile('(.*?)(?:order.*?$|\Z)',
               re.MULTILINE|re.DOTALL)

with open(filename,'r+') as f:
    x = f.read()
    f.seek(0,0)
    f.write(''.join(r.findall(x)))
    f.truncate() 

Answer 2

iterate over the file line by line (I assume you are already doing this) then use string.find :

>>> import string
>>> x = 'helloORDERme'  
>>> string.find(x,"ORDER")
5
>>> x[:string.find(x,"ORDER")]
'hello'

or if you really need to know that as well:

import string
with open('myfile', 'rU') as f:
  for line in f:
     print line[:string.find(line,"order")]

I'll leave writing the updated values back out as an excercise for the asker.

Answer 3

lines = "hello1OrderABC\nhello2OrderDEF".splitlines()
for line in lines:
  print line[:line.find("Order")]
------
hello1
hello2

First line creates a list of lines ['hello1OrderABC', 'hello2OrderDEF']. The rest iterates through this list and prints out everything upto the word "Order".