Python: search for string in a list or file

chess · 08-22-2007, 03:00 PM

Hello --

I'm working on a Python script and I have run into a roadblock that I cannot seem to overcome despite hours of google searches and trying different things. I am sure this is a simple matter, so I apologize in advance. Here is what I am trying to do.

I have a text file that has a list of filenames, one per line:

file1.txt
file2.txt
file3.txt
etc.

I have read this file into a list like so:

Code:

files = open('filenames.txt', 'r')
filelist = files.readlines()
files.close()

Now, I am trying to create a condition where something is done only if a certain string containing a new filename, say file4.txt, is _not_ in the list. For purposes of this example, the string is called "newfile". Anyway, here are some of the things I have tried:

Code:

if newfile not in filelist:
    (do stuff)


for found in filelist:
    if found.find(newfile) != 1:
        (do stuff)


for line in filelist:
     if line.find(newfile) :
         pass
    else:
        (do stuff)

for line in filelist:
    if line != newfile:
        (do stuff)

What is the right form of conditional for doing something if a string cannot be found in a list? None of these seem to work. Any assistance would be greatly appreciated. Thanks!

gizmo_thunder · 08-22-2007, 03:52 PM

the code seems correct .. the only problem i see is that
the strings in the files have a newline character at the end
of them (you cannot see it but it will be there) so try appending
a "\n" to your newfile string.. that should do the trick.

paddy3118 · 08-22-2007, 04:05 PM

Quote:

Originally Posted by chess

Hello --

I'm working on a Python script and I have run into a roadblock that I cannot seem to overcome despite hours of google searches and trying different things. I am sure this is a simple matter, so I apologize in advance. Here is what I am trying to do.

I have a text file that has a list of filenames, one per line:

file1.txt
file2.txt
file3.txt
etc.

I have read this file into a list like so:

Code:

files = open('filenames.txt', 'r')
filelist = files.readlines()
files.close()

<<SNIP>>
What is the right form of conditional for doing something if a string cannot be found in a list? None of these seem to work. Any assistance would be greatly appreciated. Thanks!

Code:

allfiles = set(f.strip() for f in filelist)
if filename not in allfiles:
  do_something()

Should do it

- Paddy.

chess · 08-22-2007, 04:22 PM

Excellent, thanks to both of you. I had not even thought about the fact the newline was at the end of each string in the file. I tried both solutions and they worked great. I appreciate the assistance.