Python list append example - divide by two

Input file:

$ cat file.txt
h1|u|1
h2|5|1|1
rec1|1239400800|Sat|fan1|AX|2|10035|-|2|50
rec2|1239400800|Sat|fan1|AX|2|-|-|2|17
rec5|1239400801|Sat|fan3|AY|5|10035|-|2|217
rec8|1239400804|Sat|fan5|AX|2|5|-|2|970

Required Output:
- Lines starting with "h1" or "h2", no action required, just print.
- Lines starting with "rec", divide the values starting from 6th field by 2.

Required output is:

h1|u|1
h2|5|1|1
rec1|1239400800|Sat|fan1|AX|1|5017|-|1|25
rec2|1239400800|Sat|fan1|AX|1|-|-|1|8
rec5|1239400801|Sat|fan3|AY|2|5017|-|1|108
rec8|1239400804|Sat|fan5|AX|1|2|-|1|485

The python script:

fp = open("file.txt", "rU")
lines = fp.readlines()
fp.close()

for line in lines:
       if line.startswith("h1"):
               print line,
       if line.startswith("h2"):
               print line,
       if line.startswith("rec"):
               f=line.split("|")
               r = f[5:]
               l = []
               for each in r:
                       try:
                               l.append(str(int(each)/2))
                       except ValueError:
                               l.append(each)

               t = "|".join(f[0:5]) + "|" + "|".join(l)
               print t.rstrip()

Print file content to output - Python

Required: Write a python program to print the content of a file to output (same as Linux/UNIX cat command do)

Way1: Using file.read file object in python

import sys,os.path

if len(sys.argv) < 2:
   print 'No file specified'
   sys.exit()
else:
   try:
      f = open(sys.argv[1], 'r')
      print f.read(),
      f.close()
   except IOError:
      print "File" + sys.argv[1] + "does not exist."

Execute it this way: To print the contents of file.txt to the output.

$ python cat-read.py file.txt

Way2: Another similar python program using file.readline

import sys

def readfile(fname):
   f = file(fname)
   while True:
      line = f.readline()
      if len(line) == 0:
         break
      print line.strip() #Avoid strip: print line,
   f.close()

if len(sys.argv) < 2:
   print 'No file specified'
   sys.exit()
else:
   readfile(sys.argv[1])

Read about python file()
In python 3.0 file() is removed.

Related concepts:

• Python file object file.close()
• Python File Objects described here