Reading/writing files in Python

Question

I am trying to create a new text file of stock symbols in the russell 2k from one that looks like this:

All I want is the ticker symbol at the end of each line. So I have the following code:

with open("russ.txt", "r") as f:
    for line in f:
        line = line.split()
        line = line[-1]
        if line == "Ticker": continue
        print line
        with open("output.txt", "w") as fh:
            fh.seek(0,2)
            print line
            fh.write(line)

All I end up with in the output.txt file is one line with the very last ticker in the list instead of all the tickers. I thought using fh.seek(0,2) would create a new line at the end each time through. What am I doing wrong? Also, in reality I don't need to create another doc, I could just edit the current one but I couldn't figure that out either so if you could show me how to just write to the same file that also is perfectly acceptable.

Answer 1

I believe using fileinput will be also handy in your case:

import fileinput
import sys


for line in fileinput.input("russ.txt", inplace=1):
    sys.stdout.write(line.split(' ')[-1])

fileinput.input will change original file.

Answer 2

The filemode "w" creates a new empty file in each step. Either use mode "a" for append, or move the file opening outside the loop.

with open("russ.txt", "r") as f:
    for line in f:
        line = line.split()
        line = line[-1]
        if line == "Ticker": continue
        print line
        with open("output.txt", "a") as fh:
            fh.write(line + "\n")

or better, open the file only once:

with open("russ.txt", "r") as f, open("output.txt", "w") as fh:
    for line in f:
        symbol = line.split()[-1]
        if symbol != "Ticker":
            print symbol
            fh.write(symbol + "\n")

Answer 3

You can read the file into a list and then use the .split() method to split it along the spaces. Since the ticekr is the last element of the list. You can get it via negative indexing.

f = [line.strip() for line in open('so.txt')]
for i in f:
    print i.split(' ')[-1]

Input file:

STARK INDUSTRIES ST
STARK INDUSTRIES ST
STARK INDUSTRIES ST
STARK INDUSTRIES ST
STARK INDUSTRIES ST

Output:

ST
ST
ST
ST
ST

Answer 4

You're overwriting the file each time you open it. Move the with line outside of the for block, and seek to the end before writing (or open in append mode).