Question

I’m trying to capture data coming across a serial in a python script. The stream ends with a ‘#’ and the stream can contain letters, numbers, many other special characters and new lines. I’d like to capture all characters and place them in a file when it finishes. I’m not sure, however, if my re is correct. Is

re.match("[A-Za-z0-9,.$:<>&*=-]", char, re.DOTALL)

going to capture all letters, numbers, and ,.$:<>&*=- characters as well as newlines? Can I simply add each char as it comes across, place it in a list and then later write the list t a file like so:

while 1:
   # must handle 'exceptions' - IE blank data....
   try:
      if s.inWaiting():
         val = s.read(s.inWaiting())
         for char in val:
            if re.match("[A-Za-z0-9,.$:<>&=-]", char, re.DOTALL):
               chunk += char
               print char

            # handle end of stream
            #if char is '#':
            if re.match("#", char):
               f = open('./report', 'w')
               f.write(chunk)
               sys.exit()

Currently it is grabbing all I expect but it does not appear to be grabbing the new lines as the resulting file does not contain any…

Answer 1

Even though you’re using re.DOTALL, your regex doesn’t actually use the dot operator. Changing line 7 to the following should work as you expect:

if re.match("[A-Za-z0-9,.$:<>&=-]|\n", char):

Works for both *nix based, and PC based newline encodings, as \r will simply be ignored by the regex.