[Tutor] "File exists, overwrite?" dialog help

[pedro]

Hi I am learning python for use in Nuke (image compositing software). I 
would like to test if a file exists and receive a warning if it does. 
To do a Nuke command line render, it looks something like this:

/Applications/Nuke5.1v5/Nuke5.1v5.app/Contents/MacOS/Nuke5.1v5 -iX 
WriteComp '/Volumes/sgtb/comp_v05.nk'

Where "WriteComp" is the name of a write node within the nuke script 
'/Volumes/sgtb/comp_v05.nk'.
The problem with the above command line command is that it overwrites 
the files that "WriteComp" points to without warning me. So what I 
would like to do is have the command line (or python) ask "File exists, 
overwrite?" Below I have some code which tests whether the file already 
exists by parsing the Nuke script. It is working fine. I am not sure 
how to combine the script below with the command line command above so 
that the above command won't be executed unless I am first asked "File 
exists, overwrite?"




#################start
import re, linecache, shutil, sys, os
theFile = (sys.argv[1])

lines = theFile.readlines()
theFile.close()

pattern = re.compile(' name WriteComp')

for i, line in enumerate(lines):
    if pattern.search(line):

        theWriteFilePath = linecache.getline(theFile.name, i-1)

#nukeFilePathAsString =

nukeFilePathContainerAsString = 
'/'.join((theWriteFilePath.split()[1]).split('/')[:-1])
nukeImageAsString = '/'.join((theWriteFilePath.split()[1]).split('/')[-1:])
nukeImageWithZeroesAsString =  nukeImageAsString.split('.')[0] + 
'.0001.' + nukeImageAsString.split('.')[2]

thePythonFriendlyFilePath = nukeFilePathContainerAsString + '/'+ 
nukeImageWithZeroesAsString
#print thePythonFriendlyFilePath

if os.path.exists(thePythonFriendlyFilePath):
    print 'yes'
#########################end


Thanks
Pete