Here we search a Python script file (or other text file) for one certain string, and copy any files containing this string to another folder.

# copy Python files containing a given string
# from source folder to destination folder
# tested with Python24  by  HAB

import os
import shutil

# supply your own folders, they have to exist!
source_folder = r"C:\Python24\Atest"
destination_folder = r"C:\Temp"
# select only Python .py files
extension = ".py"

# pick a string to search for (might be this file)
findstr = "source_folder"

for filename in os.listdir(source_folder):
    source_file = os.path.join(source_folder, filename)
    # prevent attempt to open subfolders, gives IOError
    if source_file.endswith(extension):
        if findstr in open(source_file).read():
            dest_file = os.path.join(destination_folder, filename)
            print "copied %s to %s" % (source_file, dest_file)
            shutil.copyfile(source_file, dest_file)
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