Issue
Is it possible to use python to skip blocks of text when writing a file from another file?
For example lets say the input file is:
This is the file I would like to write this line
I would like to skip this line
and this one...
and this one...
and this one...
but I want to write this one
and this one...
How can I write a script that allows me to skip certain lines that differ in content and size which resumes writing the lines to another file once it recognizes a certain line?
My code reads through the lines, doesn't write duplicate lines and performs some operation on the line by using dictionaries and regex.
Solution
def is_wanted(line):
#
# You have to define this!
#
# return True to keep the line, or False to discard it
def copy_some_lines(infname, outfname, wanted_fn=is_wanted):
with open(infname) as inf, open(outfname, "w") as outf:
outf.writelines(line for line in inf if wanted_fn(line))
copy_some_lines("file_a.txt", "some_of_a.txt")
In order to extend this to multi-line blocks, you can implement a finite state machine like
which would turn into something like
class BlockState:
GOOD_BLOCK = True
BAD_BLOCK = False
def __init__(self):
self.state = self.GOOD_BLOCK
def is_bad(self, line):
# *** Implement this! ***
# return True if line is bad
def is_good(self, line):
# *** Implement this! ***
# return True if line is good
def __call__(self, line):
if self.state == self.GOOD_BLOCK:
if self.is_bad(line):
self.state = self.BAD_BLOCK
else:
if self.is_good(line):
self.state = self.GOOD_BLOCK
return self.state
then
copy_some_lines("file_a.txt", "some_of_a.txt", BlockState())
Answered By - Hugh Bothwell Answer Checked By - Clifford M. (PHPFixing Volunteer)
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