This python routine is designed to search a table (usually the VIRUS_IFU.table made by a run of vir_ifu_pat.sh) and print information for a user-requested IFUSLOT value. The task is simple, but I show the entire python code below since it incorporates a number of newly gained skills (as of July 2015) regarding file reading and error checking. To start with, I show a normal run on a modified VIRUS_IFU.table file that I have renamed "A". The point here is that "A" has a bad data line (the Xcen value for ifuslot=040 is not a number), and the dX,dY values for ifuslot=030 have nonzero values.

 
% vtabread.py A 030
-44240.000000 -79670.000000 -90.000000

% cat A 
# VIRUS IFU Table:  Tue Jul  7 13:15:21 CDT 2015  
# linear units: microns   
col01 = IFU slot name (ccr)  {t1,a3}
col02 = Xcen  { t5,f12.3}                
col03 = Ycen  {t18,f12.3}                
col04 = Theta {t34,f10.5} degrees        
col05 = dx    {t48,f9.3}                
col06 = dy    {t58,f9.3}                
col07 = scale {t72,f6.2}  microns/arcsec
# data
030   -44250.000   -79650.000     -90.00000       10.000   -20.000     177.00
040   nnnnnnnnnn   -79650.000     -90.00000        0.000     0.000     177.00
050    -8850.000   -79650.000     -90.00000        0.000     0.000     177.00
035   -44250.000     8850.000     -90.00000        0.000     0.000     177.00

Below I show the usual type of useful output we would get if we invoke the "-h" or "--help" flags:

 
% vtabread.py --help 
usage: vtabread.py [-h] [-v] arg1 arg2

positional arguments:
  arg1           input file (VIRUS_IFU.table)
  arg2           IFUSLOT number (ccr)

optional arguments:
  -h, --help     show this help message and exit
  -v, --verbose  Verbose responses

Finally, I show below a case where we have requested an IFUSLOT that does have an entry in our table, but that data entry has a corrupt value. We send the output to a file named "a.out", and then we see that a.out is empty. The important point here is that requesting the bad case (ifuslot=040) does NOT cause vtabread.py to crash. We can handle the empty contents of "a.out" later, but if vtabread.py crashes in the middle of some larger processing script, then we'd generally be SOL at that point.

 
% vtabread.py A 040 >a.out 
% cat a.out 
% 

Below is the code for vtabread.py.

#!/usr/bin/python
""" Read the IFU table (typically a file named 
    VIRUS_IFU.table made with vir_ifu_pat.sh) and 
    extract the X,Y positions for a requested IFU 
    slot position (ccr notation). 
    S. Odewahn July2015 """

import argparse as ARGP
parser = ARGP.ArgumentParser()
parser.add_argument("arg1", help="input file (VIRUS_IFU.table)")
parser.add_argument("arg2", help="IFUSLOT number (ccr)")
parser.add_argument("-v","--verbose", help="Verbose responses", action="store_true")
args = parser.parse_args()

fileXY = args.arg1
ifuslot = args.arg2

if args.verbose:
 print "Input file        = %s\n" % (fileXY),
 print "IFUSLOT requested = %s\n" % (ifuslot),

#==================================================
#==================================================
# Open the file for read-only 
f = open(fileXY, 'r')

# Look until you find the string "# data"
for line in f:
 p = line.split()
 if (len(p) == 2):
  if p[0] == "#" and p[1] == "data":
    if args.verbose:
     print "found the string"
    break  
 
# Read the data lines
fname = []
xr = []
yr = []
pa = []
dx = []
dy = []
i = 0
for line in f:
 if args.verbose:
  print line,

# split up the input data line into words
 p = line.split()

#++++++++++++++++++++++++++++++++++++++++++++++++++++
# Check all data values 

# Check that the Xcen value is a readable float 
 try:
  a_x = float(p[1])
  xchek = "OK"
 except:
  a_x = -999.99
  xchek = "BAD"
 if args.verbose:
   print "a_x,xchek : %f %s\n" % (a_x,xchek),

# Check that the Ycen value is a readable float 
 try:
  a_y = float(p[2])
  ychek = "OK"
 except:
  a_y = -999.99
  ychek = "BAD"
 if args.verbose:
   print "a_y,ychek : %f %s\n" % (a_y,ychek),

# Check that the PA value is a readable float 
 try:
  par = float(p[3])
  pachek = "OK"
 except:
  par = -999.99
  pachek = "BAD"
 if args.verbose:
   print "par,pachek : %f %s\n" % (par,pachek),

# Check that the dX value is a readable float 
 try:
  dxr = float(p[4])
  dxchek = "OK"
 except:
  dxr = -999.99
  dxchek = "BAD"
 if args.verbose:
   print "dxr,dxchek : %f %s\n" % (dxr,dxchek),

# Check that the dY value is a readable float 
 try:
  dyr = float(p[5])
  dychek = "OK"
 except:
  dyr = -999.99
  dychek = "BAD"
 if args.verbose:
   print "dyr,dychek : %f %s\n" % (dyr,dychek),
#++++++++++++++++++++++++++++++++++++++++++++++++++++

 icheck = 0 
 if xchek!="BAD":
  icheck = icheck+1
 if ychek!="BAD":
  icheck = icheck+1
 if pachek!="BAD":
  icheck = icheck+1  
 if dxchek!="BAD":
  icheck = icheck+1  
 if dychek!="BAD": 
  icheck = icheck+1  

# print p[0],icheck

# if all tests were passed (i.e. icheck=5) then store the data  
 if icheck == 5:
  fname.append(p[0])  
  xr.append(a_x)
  yr.append(a_y)
  pa.append(par)
  dx.append(dxr)
  dy.append(dyr)
  i=i+1

n = i 

if args.verbose:
 print "The number of valid DATA lines = %d\n" % (n) 

# close the input file 
f.close() 
#==================================================
#==================================================

# Print the fname values that you read from the file 
i = 0 
while i < n:
 if args.verbose:
  print "fname(%d) = %s\n" % (i,fname[i]),
 if fname[i] == ifuslot:
  xfinal = xr[i] + dx[i]
  yfinal = yr[i] + dy[i]
  print "%f %f %f" % (xr[i]+dx[i], yr[i]+dy[i], pa[i]),
  break
 i=i+1