[Tutor] Multiple file open

[Sander Sweers]

On 18 August 2010 17:14, nitin chandra <nitinchandra1 at gmail.com> wrote:
> I am on Python 2.6
>
<snipped a whole lot of text>

> Please guide with the syntax.

All beginners tutorials on the web teach the syntax of python.. I am
unsure what your questions is.

> below is the existing program with Formula A (Mean). Formula B will be
> Extrapolation,
> also I have not been able to do justice to 'except IOError:' part.The

It has many errors which need fixing but..

> program ends with an error.

And if you get an error always make sure you provide it to this list.
People on this list can not read minds ;-).

> ********************************
> import sys,os, fileinput
>
>
> file11 = raw_input('Enter PR1 File name :')
> fp1 = open(file11,'r')
>
> file12 = raw_input('Enter PR3 File Name :')
> fp2 = open(file12,'r')
>
> file3 = raw_input('Enter PR2 / PR4 OUTPUT File Name :')
> fp3 = open(file3,'w')

What happens when you enter a wrong filename? It will raise IOError
the moment you use open(). Below is 1 example of what you might want
tot do.

file11 = raw_input('Enter PR1 File name :')
try:
    fp1 = open(ffile11, 'r')
except IOError:
   sys.exit('Could not open file: %s' % file11)

> while True:
>   try:
>       line1A = fp1.readline()

You can read and split the line in 1 go.
         line1 = fp1.readline().split(",")

>       line1B = fp2.readline()
>       line1 = line1A.split(",")

You can now remove the above, see earlier comment.

>       col1 = line1[0]
>       col2 = line1[1]
>       col3 = line1[2]
>       col4 = line1[3]
>       col5 = line1[20]
>       col6 = line1[21]
>       col7 = line1[22]
>       line2 = line1B.split(",")
>       col8 = line2[1]
>       col9 = line2[2]
>       col10 = line2[3]
>       col11 = line2[20]
>       col12 = line2[21]
>       col13 = line2[22]

Above you create a list "line1 = fp1.readline().split(",")". Lists are
mutable so you can add, remove and insert new items. You can also
access the items in the list by index. You can even add 2 lists to
make a new list, eg: .

>>> [1,2,3,4,5] + [6,7,8,9,0]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]

Now try and apply this to all your col<num> variables.

>       # calculation of PR2 as per formula
>       #(A+B)/2 , ie. Mean of the two values
>       col14 = ( (float(col2)) + (float(col8)) / 2)

You can write this as:
  col14 = (float(line1[1])) + (float(line2[1])) / 2)

And avoid creating all these col variables. But what would happen if
col2/line1[1] has a value of "I am not a number"? Do note the comment
below on the actual calculation.

>       col15 = ( (float(col3)) + (float(col9)) / 2)
<snipped some more>
>       col19 = ( (float(col7)) + (float(col13)) / 2)

Your "mean" calculation is wrong (hint, division has precedence over adding).

Greets
Sander