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Simple text parsing gets difficult when line continues to next line

P: n/a
Hello,

I have a simple script to parse a text file (a visual basic program)
and convert key parts to tcl. Since I am only working on specific
sections and I need it quick, I decided not to learn/try a full blown
parsing module. My simple script works well until it runs into
functions that straddle multiple lines. For example:

Call mass_write(&H0, &HF, &H4, &H0, &H5, &H0, &H6, &H0, &H7, &H0,
&H8, &H0, _
&H9, &H0, &HA, &H0, &HB, &H0, &HC, &H0, &HD, &H0, &HE,
&H0, &HF, &H0, -1)
I read in each line with:

for line in open(fileName).readlines():

I would line to identify if a line continues (if line.endswith('_'))
and concate with the next line:

line = line + nextLine

How can I get the next line when I am in a for loop using readlines?

jr

Nov 28 '06 #1
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6 Replies


P: n/a
Jacob Rael wrote:
Hello,

I have a simple script to parse a text file (a visual basic program)
and convert key parts to tcl. Since I am only working on specific
sections and I need it quick, I decided not to learn/try a full blown
parsing module. My simple script works well until it runs into
functions that straddle multiple lines. For example:

Call mass_write(&H0, &HF, &H4, &H0, &H5, &H0, &H6, &H0, &H7, &H0,
&H8, &H0, _
&H9, &H0, &HA, &H0, &HB, &H0, &HC, &H0, &HD, &H0, &HE,
&H0, &HF, &H0, -1)
I read in each line with:

for line in open(fileName).readlines():

I would line to identify if a line continues (if line.endswith('_'))
and concate with the next line:

line = line + nextLine

How can I get the next line when I am in a for loop using readlines?

jr
Something like (not tested):

fp=open(filename, 'r')
for line in fp:
while line.rstrip().endswith('_'):
line+=fp.next()
fp.close()

-Larry

Nov 28 '06 #2

P: n/a
Jacob Rael wrote:
[...]
I would line to identify if a line continues (if line.endswith('_'))
and concate with the next line:

line = line + nextLine

How can I get the next line when I am in a for loop using readlines?
Don't use readlines.

# NOT TESTED
program = open(fileName)
for line in program:
while line.rstrip("\n").endswith("_"):
line = line.rstrip("_ \n") + program.readline()
do_the_magic()

Cheers,
--
Roberto Bonvallet
Nov 28 '06 #3

P: n/a
Jacob Rael wrote:
Hello,

I have a simple script to parse a text file (a visual basic program)
and convert key parts to tcl. Since I am only working on specific
sections and I need it quick, I decided not to learn/try a full blown
parsing module. My simple script works well until it runs into
functions that straddle multiple lines. For example:

Call mass_write(&H0, &HF, &H4, &H0, &H5, &H0, &H6, &H0, &H7, &H0,
&H8, &H0, _
&H9, &H0, &HA, &H0, &HB, &H0, &HC, &H0, &HD, &H0, &HE,
&H0, &HF, &H0, -1)
I read in each line with:

for line in open(fileName).readlines():

I would line to identify if a line continues (if line.endswith('_'))
and concate with the next line:

line = line + nextLine

How can I get the next line when I am in a for loop using readlines?
Don't do that. I'm rather dubious about approaches that try to grab the
next line on the fly e.g. fp.next(). Here's a function that takes a
list of lines and returns another with all trailing whitespace removed
and the continued lines glued together. It uses a simple state machine
approach.

def continue_join(linesin):
linesout = []
buff = ""
NORMAL = 0
PENDING = 1
state = NORMAL
for line in linesin:
line = line.rstrip()
if state == NORMAL:
if line.endswith('_'):
buff = line[:-1]
state = PENDING
else:
linesout.append(line)
else:
if line.endswith('_'):
buff += line[:-1]
else:
buff += line
linesout.append(buff)
buff = ""
state = NORMAL
if state == PENDING:
raise ValueError("last line is continued: %r" % line)
return linesout

import sys
fp = open(sys.argv[1])
rawlines = fp.readlines()
cleanlines = continue_join(rawlines)
for line in cleanlines:
print repr(line)
===
Tested with following files:
C:\junk>type contlinet1.txt
only one line

C:\junk>type contlinet2.txt
line 1
line 2

C:\junk>type contlinet3.txt
line 1
line 2a _
line 2b _
line 2c
line 3

C:\junk>type contlinet4.txt
line 1
_
_
line 2c
line 3

C:\junk>type contlinet5.txt
line 1
_
_
line 2c
line 3 _

C:\junk>

HTH,
John

Nov 28 '06 #4

P: n/a
John Machin wrote:
Jacob Rael wrote:
>Hello,

I have a simple script to parse a text file (a visual basic program)
and convert key parts to tcl. Since I am only working on specific
sections and I need it quick, I decided not to learn/try a full blown
parsing module. My simple script works well until it runs into
functions that straddle multiple lines. For example:

Call mass_write(&H0, &HF, &H4, &H0, &H5, &H0, &H6, &H0, &H7, &H0,
&H8, &H0, _
&H9, &H0, &HA, &H0, &HB, &H0, &HC, &H0, &HD, &H0, &HE,
&H0, &HF, &H0, -1)
I read in each line with:

for line in open(fileName).readlines():

I would line to identify if a line continues (if line.endswith('_'))
and concate with the next line:

line = line + nextLine

How can I get the next line when I am in a for loop using readlines?

Don't do that. I'm rather dubious about approaches that try to grab the
next line on the fly e.g. fp.next(). Here's a function that takes a
list of lines and returns another with all trailing whitespace removed
and the continued lines glued together. It uses a simple state machine
approach.
I agree that mixing the line assembly and parsing is probably a mistake
although using next explicitly is fine as long as your careful with it.
For instance, I would be wary to use the mixed for-loop, next strategy
that some of the previous posts suggested. Here's a different,
generator-based implementation of the same idea that, for better or for
worse is considerably less verbose:

def continue_join_2(linesin):
getline = iter(linesin).next
while True:
buffer = getline().rstrip()
try:
while buffer.endswith('_'):
buffer = buffer[:-1] + getline().rstrip()
except StopIteration:
raise ValueError("last line is continued: %r" % line)
yield buffer

-tim

[SNIP]

Nov 28 '06 #5

P: n/a

Tim Hochberg wrote:
[snip]
I agree that mixing the line assembly and parsing is probably a mistake
although using next explicitly is fine as long as your careful with it.
For instance, I would be wary to use the mixed for-loop, next strategy
that some of the previous posts suggested. Here's a different,
generator-based implementation of the same idea that, for better or for
worse is considerably less verbose:
[snip]

Here's a somewhat less verbose version of the state machine gadget.

def continue_join_3(linesin):
linesout = []
buff = ""
pending = 0
for line in linesin:
# remove *all* trailing whitespace
line = line.rstrip()
if line.endswith('_'):
buff += line[:-1]
pending = 1
else:
linesout.append(buff + line)
buff = ""
pending = 0
if pending:
raise ValueError("last line is continued: %r" % line)
return linesout

FWIW, it works all the way back to Python 2.1

Cheers,
John,

Nov 28 '06 #6

P: n/a
Thanks all. I think I'll follow the "don't do that" advice.

jr

Jacob Rael wrote:
Hello,

I have a simple script to parse a text file (a visual basic program)
and convert key parts to tcl. Since I am only working on specific
sections and I need it quick, I decided not to learn/try a full blown
parsing module. My simple script works well until it runs into
functions that straddle multiple lines. For example:

Call mass_write(&H0, &HF, &H4, &H0, &H5, &H0, &H6, &H0, &H7, &H0,
&H8, &H0, _
&H9, &H0, &HA, &H0, &HB, &H0, &HC, &H0, &HD, &H0, &HE,
&H0, &HF, &H0, -1)
I read in each line with:

for line in open(fileName).readlines():

I would line to identify if a line continues (if line.endswith('_'))
and concate with the next line:

line = line + nextLine

How can I get the next line when I am in a for loop using readlines?

jr
Nov 28 '06 #7

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