Simple python file lookup function for newbie

Config file 'ip-mapping.txt' is a file of the following format:

$ cat /home/testusr/work/ip-mapping.txt
#id:ip1,ip2,ip3
200:172.17.4.12,172.17.4.14,172.17.4.10
205:172.17.4.14,172.17.4.14,172.17.4.11
210:172.17.4.12,172.17.4.18,172.17.4.18
208:172.17.4.11,172.17.4.10,172.17.4.19

Required: Create a simple python function which will accept an 'id' and will return 'ip1' from the list of ips.

The python script:

import os,sys

config = '/home/testusr/work/ip-mapping.txt'
if not os.path.exists(config):
    print config+' file not present'
    sys.exit()

def getip(id):
   all = open(config).readlines()
   for line in all:
        if line.startswith('#'):
            continue
        f=line.split(":")
        if f[0]==id:
                return f[1].split(',')[0]

ip=getip('205')
print ip

Executing it:

$ python get-ip.py
172.17.4.14

I am sure there will be much better solutions to this problem, please comment, really appreciated.

The description about Exit function of 'sys' module (source) :

sys.exit([arg])
Exit from Python. This is implemented by raising the SystemExit exception, so cleanup actions
specified by finally clauses of try statements are honored, and it is possible to intercept the exit
attempt at an outer level. The optional argument arg can be an integer giving the exit status
(defaulting to zero), or another type of object. If it is an integer, zero is considered “successful
termination” and any nonzero value is considered “abnormal termination” by shells and the
like. Most systems require it to be in the range 0-127, and produce undefined results otherwise.

Some systems have a convention for assigning specific meanings to specific exit codes, but these
are generally underdeveloped; Unix programs generally use 2 for command line syntax errors
and 1 for all other kind of errors. If another type of object is passed, None is equivalent to
passing zero, and any other object is printed to sys.stderr and results in an exit code of 1. In
particular, sys.exit("some error message") is a quick way to exit a program when an error occurs.

Related posts on lookup on file using python:

• Lookup file in python using dictionary
• Find text string in file using python
• Lookup file operation in python
  

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

Truncate file extension using python glob

My current directory contains the following 2 files.

$ ls -1
20061117.dat.dat
details.dat.dat.dat

Required: Move(rename) the above files to single .dat extension (e.g. details.dat.dat.dat to details.dat)
The python code using glob module:

>>> import os,glob
>>> for file in glob.glob("*.dat"):
...     newF=".".join(file.split(".")[:2])
...     os.rename(file,newF)
...

Now:

$ ls -1
20061117.dat
details.dat

Using glob module we can use wildcards with Python according to the rules used by the Unix shell. More about it can be found here

Few more examples:

# lists all files in the current directory
glob.glob('*')

# returns all .dat extension files
glob.glob('*.dat')

# lists all files starting with a letter, followed by 3 characters (numbers, letters) and any ending.
glob.glob('[a-z]???.*')

Move files based on condition in python

Contents of /tmp/mydir/

$ ls /tmp/mydir/ | paste -

logWA241.dat
logWA249.dat
logWA258.dat
logWA259.dat

Required: Move the above files to directories under /tmp/mydir such that logWA241.dat should go to dir /tmp/mydir/1, similarly logWA258.dat to /tmp/mydir/8 (i.e. dir name with last digit before .dat extn)

The python script:

import os
DIR="/tmp/mydir"
for file in os.listdir(DIR):
   Absfile = os.path.join(DIR,file)
   if os.path.isfile(Absfile) and file.endswith(".dat"):
       Dname = Absfile.split(".")[:-1][-1][-1:]
       Dname = os.path.join(DIR,Dname)
       if not os.path.exists(Dname):
           os.mkdir(Dname)
           os.system('mv '+Absfile+' '+Dname)
       else:
           os.system('mv '+Absfile+' '+Dname)

The contents of /tmp/mydir/ after exection of the above script.

$ ls -R /tmp/mydir/

o/p:

/tmp/mydir/:
1  8  9

/tmp/mydir/1:
logWA241.dat

/tmp/mydir/8:
logWA258.dat

/tmp/mydir/9:
logWA249.dat  logWA259.dat

Related concepts and modules:
- Python os module