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Looking for Form Feeds

P: n/a
Hello-
I have a file generated by an HP-9000 running Unix containing form feeds
signified by ^M^L. I am trying to scan for the linefeed to signal
certain processing to be performed but can not get the regex to "see"
it. Suppose I read my input line into a variable named "input"

The following does not seem to work...
input = input_file.readline()
if re.match('\f', input): print 'Found a formfeed!'
else: print 'No linefeed!'

I also tried to create a ^M^L (typed in as <ctrl>Q M <ctrlQ> L) but that
gives me a syntax error when I try to run the program (re does not like
the control characters, I guess). Is it possible for me to pull out the
formfeeds in a straightforward manner?

Thanks!
--greg

--
Greg Lindstrom 501 975.4859
Computer Programmer gr************@novasyshealth.com
NovaSys Health
Little Rock, Arkansas

"We are the music makers, and we are the dreamers of dreams." W.W.

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Jul 18 '05 #1
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P: n/a
Greg Lindstrom wrote:
I have a file generated by an HP-9000 running Unix containing form feeds
signified by ^M^L. I am trying to scan for the linefeed to signal
certain processing to be performed but can not get the regex to "see"
it. Suppose I read my input line into a variable named "input"

The following does not seem to work...
input = input_file.readline()
if re.match('\f', input): print 'Found a formfeed!'
else: print 'No linefeed!'

I also tried to create a ^M^L (typed in as <ctrl>Q M <ctrlQ> L) but that
gives me a syntax error when I try to run the program (re does not like
the control characters, I guess). Is it possible for me to pull out the
formfeeds in a straightforward manner?


What's happening is that you're using .match, so you're only checking
for matches at the _start_ of the string, not anywhere within it.

It's easier than you think actually; you're just looking for substrings,
so searching with .find on strings is probably sufficient:

if line.find('\f') >= 0: ...

If you want to look for ^M^L, that'd be '\r\f':

if line.find('\r\f') >= 0: ...

If you want to keep a running count, you can use .count, which will
count the number of substrings in the line.

--
Erik Max Francis && ma*@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
I would have liked to have seen Montana.
-- Capt. Vasily Borodin
Jul 18 '05 #2

P: n/a
Greg Lindstrom wrote:
Hello-
I have a file generated by an HP-9000 running Unix containing form feeds signified by ^M^L. I am trying to scan for the linefeed to signal
certain processing to be performed but can not get the regex to "see" it. Suppose I read my input line into a variable named "input"

The following does not seem to work...
input = input_file.readline()
You are shadowing a builtin.
if re.match('\f', input): print 'Found a formfeed!'
else: print 'No linefeed!'
formfeed == not not linefeed????

I also tried to create a ^M^L (typed in as <ctrl>Q M <ctrlQ> L) but that gives me a syntax error when I try to run the program (re does not like the control characters, I guess). Is it possible for me to pull out the formfeeds in a straightforward manner?


For a start, resolve your confusion between formfeed and linefeed.

Formfeed makes your printer skip to the top of a new page (form),
without changing the column position. FF, '\f', ctrl-L, 0x0C.
Linefeed makes the printer skip to a new line, without changing the
column position. LF, '\n', ctrl-J, 0x0D.
There is also carriage return, which makes your typewriter return to
column 1, without moving to the next line. CR, '\r', ctrl-M, 0x0A.

Now you can probably guess why the writer of your report file is
emitting "\r\f". What we can't guess for you is where in your file
these "\r\f" occurrences are in relation to the newlines (i.e. '\n')
which Python is interpreting as line breaks. As others have pointed
out, (1) re.match works on the start of the string and (2) you probably
don't need to use re anyway. The solution may be as simple as: if
input_line[:2] == "\r\f":

BTW, have you checked that there are no other control characters
embedded in the file, e.g. ESC (introducing an escape sequence), SI/SO
(change character set), BEL * 100 (Hey, Fred, the printout's finished),
HT, VT, BS (yeah, probably lots of that, but I mean BackSpace)?
HTH,
John

Jul 18 '05 #3

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