Re: [Tutor] Working with lines from file and printing to another keeping sequential order
Le Mon, 27 Apr 2009 23:29:13 -0400,
Dan Liang s'exprima ainsi:
> Hi Bob, Shantanoo, Kent, and tutors,
>
> Thank you Bob, Shantanoo, Kent for all the nice feedback. Exception
> handling, the concept of states in cs, and the use of the for loop with
> offset helped a lot. Here is the code I now have, based on your suggestions,
> and it does what I need:
>
> ListLines = [ line.rstrip() for line in open('test.txt') ]
>
> countYes = 0
> countNo = 0
>
> for i in range(len(ListLines)):
> if ListLines[i].endswith('yes'):
> countYes+=1
> print "countYes", countYes, "\t\t", ListLines[i]
>
> if not ListLines[i].endswith('yes'):
> continue
>
> for offset in (1, 2, 3, 4, 5, 6, 7, 8):
> if i+offset < len(ListLines) and ListLines[i+offset].endswith('no'):
>
>countNo+=1
>
>print "countNo", countNo, "\t\t", ListLines[i+offset]
It probably works, but there is something uselessly complicated, logically
speaking:
-1- case ends with 'yes', do
-2- case not ends with 'yes', do
-3- case ends with 'yes', again, do
You'd better group -1- and -3-, no? Moreover, as action -2- is to continue,
further code is simplified if -2- is placed first:
for i in range(len(ListLines)):
if not ListLines[i].endswith('yes'):
continue
# case line ends with 'yes': process it
countYes+=1
print "countYes", countYes, "\t\t", ListLines[i]
for offset in (1, 2, 3, 4, 5, 6, 7, 8):
if i+offset < len(ListLines) and ListLines[i+offset].endswith('no'):
countNo+=1
print "countNo", countNo, "\t\t", ListLines[i+offset]
Also, use more than 1 space for indent, and be consistent (set the value in
your editor settings and use the TAB key to achieve that); and avoid too many
useless blank lines.
Denis
--
la vita e estrany
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Re: [Tutor] Working with lines from file and printing to another keeping sequential order
Hi Bob, Shantanoo, Kent, and tutors,
Thank you Bob, Shantanoo, Kent for all the nice feedback. Exception
handling, the concept of states in cs, and the use of the for loop with
offset helped a lot. Here is the code I now have, based on your suggestions,
and it does what I need:
ListLines = [ line.rstrip() for line in open('test.txt') ]
countYes = 0
countNo = 0
for i in range(len(ListLines)):
if ListLines[i].endswith('yes'):
countYes+=1
print "countYes", countYes, "\t\t", ListLines[i]
if not ListLines[i].endswith('yes'):
continue
for offset in (1, 2, 3, 4, 5, 6, 7, 8):
if i+offset < len(ListLines) and ListLines[i+offset].endswith('no'):
countNo+=1
print "countNo", countNo, "\t\t", ListLines[i+offset]
Thank you again!
--dan
On Sun, Apr 26, 2009 at 10:55 AM, Kent Johnson wrote:
> On Sat, Apr 25, 2009 at 2:11 PM, Dan Liang wrote:
> > Hi Bob and tutors,
> >
> > Thanks Bob for your response! currently I have the current code, but it
> does
> > not work:
> >
> > ListLines= []
> > for line in open('test.txt'):
> > line = line.rstrip()
> > ListLines.append(line)
>
> This could be written with a list comprehension:
> ListLines = [ line.rstrip() for line in open('test.txt') ]
>
> >
> > for i in range(len(ListLines)):
> >
> > if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
> > ListLines[i+1].endswith("no"):
> > print ListLines[i], ListLines[i+1], ListLines[i+2]
> > elif ListLines[i].endswith("yes") and ListLines[i+1].endswith("no"):
> > print ListLines[i], ListLines[i+1]
> > elif ListLines[i].endswith("yes"):
> > print ListLines[i]
> > elif ListLines[i].endswith("no"):
> > continue
> > else:
> > break
>
> You only need to test for ListLines[i].endswith('yes') once. Then you
> could use a loop to test for lines ending with 'no'.
>
> for i in range(len(ListLines)):
> if not ListLines[i].endswith('yes'):
>continue
> for offset in (1, 2):
>if i+offset < len(ListLines) and ListLines[i+offset].endswith('no'):
> print ListLines[i+offset]
>
> You could adapt the above for a variable number of 'no' lines with
> something like
> for offset in range(1, maxNo+1):
>
> > I get the following error:
> > Traceback (most recent call last):
> > File "test.py", line 18, in
> > if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
> > ListLines[i+1].endswith("no"):
> > IndexError: list index out of range
>
> That is because you have a 'yes' line at the end of the file so the
> check for 'no' tries to read past the end of ListLines. In my code the
> test for i+offset < len(ListLines) will prevent that exception.
>
> Kent
>
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Re: [Tutor] Working with lines from file and printing to another keeping sequential order
On Sat, Apr 25, 2009 at 2:11 PM, Dan Liang wrote:
> Hi Bob and tutors,
>
> Thanks Bob for your response! currently I have the current code, but it does
> not work:
>
> ListLines= []
> for line in open('test.txt'):
> line = line.rstrip()
> ListLines.append(line)
This could be written with a list comprehension:
ListLines = [ line.rstrip() for line in open('test.txt') ]
>
> for i in range(len(ListLines)):
>
> if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
> ListLines[i+1].endswith("no"):
> print ListLines[i], ListLines[i+1], ListLines[i+2]
> elif ListLines[i].endswith("yes") and ListLines[i+1].endswith("no"):
> print ListLines[i], ListLines[i+1]
> elif ListLines[i].endswith("yes"):
> print ListLines[i]
> elif ListLines[i].endswith("no"):
> continue
> else:
> break
You only need to test for ListLines[i].endswith('yes') once. Then you
could use a loop to test for lines ending with 'no'.
for i in range(len(ListLines)):
if not ListLines[i].endswith('yes'):
continue
for offset in (1, 2):
if i+offset < len(ListLines) and ListLines[i+offset].endswith('no'):
print ListLines[i+offset]
You could adapt the above for a variable number of 'no' lines with
something like
for offset in range(1, maxNo+1):
> I get the following error:
> Traceback (most recent call last):
> File "test.py", line 18, in
> if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
> ListLines[i+1].endswith("no"):
> IndexError: list index out of range
That is because you have a 'yes' line at the end of the file so the
check for 'no' tries to read past the end of ListLines. In my code the
test for i+offset < len(ListLines) will prevent that exception.
Kent
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Re: [Tutor] Working with lines from file and printing to another keeping sequential order
Dan Liang wrote:
Hi Bob and tutors,
Thanks Bob for your response! currently I have the current code, but
it does not work:
[snip]
Thank you for code, sample data and more complete specs.
Lines in the file look like following:
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
Any suggestions are appreciated. Also, I feel that my code is not the
best way of solving the problem even if the problem of list indices is
solved. Is my guess right?
Yes indeed. In actuality you need only to examine one line at a time and
keep track of the "state" of things.
In computer theory we refer to a "state machine". There is a set of
states. The program is always in exactly one of these states. In each
state there are actions to take and a (conditional) moves to other states.
the program starts in, let's say, state 0:
state 0: open file, goto state 1.
state 1: read next line, at eof goto state 6; if it ends in yes, goto
state 2 else stay in state 1.
state 2: read next line, at eof goto state 6; if it ends in yes stay in
state 2 else goto state 3.
state 3: read next line, at eof goto state 6. if it ends in yes goto
state 2 else print line and goto state 4.
state 4: read next line, at eof goto state 6. if it ends in yes goto
state 2 else print line and goto state 5.
state 5: read next line, at eof goto state 6. if it ends in yes goto
state 2 else stay in state 5.
state 6: close file and terminate
That can be implemented in Python as follows. This is not the prettiest
or most compact program, but is it a straightforward implementation of a
state machine.
state = 0 # initial state
data = open('test.txt')
while True: # iterate over lines
if state == 0: # look for first line ending in 'yes'
line = data.read().strip()
if line:
if line.endswith('yes'):
state = 1
else state = 6
elif state == 1:
# code for state i
# more states
elif state == 6:
data.close()
break
To simplify things I'd create a function to read and strip a line and
raise an exception at end of file.
--
Bob Gailer
Chapel Hill NC
919-636-4239
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Re: [Tutor] Working with lines from file and printing to another keeping sequential order
On 25-Apr-09, at 11:41 PM, Dan Liang wrote:
Hi Bob and tutors,
Thanks Bob for your response! currently I have the current code, but
it does not work:
ListLines= []
for line in open('test.txt'):
line = line.rstrip()
ListLines.append(line)
for i in range(len(ListLines)):
if ListLines[i].endswith("yes") and ListLines[i
+1].endswith("no") and ListLines[i+1].endswith("no"):
print ListLines[i], ListLines[i+1], ListLines[i+2]
elif ListLines[i].endswith("yes") and ListLines[i
+1].endswith("no"):
print ListLines[i], ListLines[i+1]
elif ListLines[i].endswith("yes"):
print ListLines[i]
elif ListLines[i].endswith("no"):
continue
else:
break
I get the following error:
Traceback (most recent call last):
File "test.py", line 18, in
if ListLines[i].endswith("yes") and ListLines[i
+1].endswith("no") and ListLines[i+1].endswith("no"):
IndexError: list index out of range
You need to put check for
i <= len(ListLines)-2
or you can have a look @ try and except (exception handling in python)
Lines in the file look like following:
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
> What do we do at steps 4ff if the line does not end in "yes" or
"no"?
I forgot to mention that I know for sure that the file has ONLY
lines that end in either "yes" or "no".
Any suggestions are appreciated. Also, I feel that my code is not
the best way of solving the problem even if the problem of list
indices is solved. Is my guess right?
Another suggestion. I would not read all data from file into array
(memory). If your file is large, you may hit out of memory error.
regards,
shantanoo
Thank you!
-dan
On Sat, Apr 25, 2009 at 10:32 AM, bob gailer
wrote:
Dan Liang wrote:
Dear Tutors,
I have a file from which I want to extract lines that end in certain
strings and print to a second file. More specifically, I want to:
1) iterate over each line in the file, and if it ends in "yes",
print it.
2) move to the line following the one described in #1 above, and if
it ends in, "no" print it.
3) move to third line, and if it ends in "no", print it.
4) move to fourth line, and if it ends in "no" discard it, but if it
ends in "yes" repeat 1, 2, and 3 above.
5) move to fifth line, and if it ends in "no" discard it, but if it
ends in "yes" repeat 1, 2, 3, and 4 above, and so on.
The goal is to get a ratio of 1 to 2 "yes" to "no" lines from a file
in such a way that keeps the order of the lines in output. An
abstraction away from this so that any ratio of "yes" to "no" lines
could be printed while keeping the order of the original lines would
be great.
Please show us what code you have written, and in what way it fails
to meet your expectations.
Your specification is IMHO a nice piece of pseudocode which could
translate to Python fairly easily!
What do we do at steps 4ff if the line does not end in "yes" or "no"?
If you have not written any code make a stab at it. You could start
by asking "how in Python does one":
open a file?
iterate (loop)?
get the next line from a file?
test for equality?
examine the end of a string?
--
Bob Gailer
Chapel Hill NC
919-636-4239
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Re: [Tutor] Working with lines from file and printing to another keeping sequential order
Hi Bob and tutors,
Thanks Bob for your response! currently I have the current code, but it does
not work:
ListLines= []
for line in open('test.txt'):
line = line.rstrip()
ListLines.append(line)
for i in range(len(ListLines)):
if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
ListLines[i+1].endswith("no"):
print ListLines[i], ListLines[i+1], ListLines[i+2]
elif ListLines[i].endswith("yes") and ListLines[i+1].endswith("no"):
print ListLines[i], ListLines[i+1]
elif ListLines[i].endswith("yes"):
print ListLines[i]
elif ListLines[i].endswith("no"):
continue
else:
break
I get the following error:
Traceback (most recent call last):
File "test.py", line 18, in
if ListLines[i].endswith("yes") and ListLines[i+1].endswith("no") and
ListLines[i+1].endswith("no"):
IndexError: list index out of range
Lines in the file look like following:
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
> What do we do at steps 4ff if the line does not end in "yes" or "no"?
I forgot to mention that I know for sure that the file has ONLY lines that
end in either "yes" or "no".
Any suggestions are appreciated. Also, I feel that my code is not the best
way of solving the problem even if the problem of list indices is solved. Is
my guess right?
Thank you!
-dan
On Sat, Apr 25, 2009 at 10:32 AM, bob gailer wrote:
> Dan Liang wrote:
>
>> Dear Tutors,
>>
>>
>> I have a file from which I want to extract lines that end in certain
>> strings and print to a second file. More specifically, I want to:
>>
>> 1) iterate over each line in the file, and if it ends in "yes", print it.
>> 2) move to the line following the one described in #1 above, and if it
>> ends in, "no" print it.
>> 3) move to third line, and if it ends in "no", print it.
>> 4) move to fourth line, and if it ends in "no" discard it, but if it ends
>> in "yes" repeat 1, 2, and 3 above.
>> 5) move to fifth line, and if it ends in "no" discard it, but if it ends
>> in "yes" repeat 1, 2, 3, and 4 above, and so on.
>>
>> The goal is to get a ratio of 1 to 2 "yes" to "no" lines from a file in
>> such a way that keeps the order of the lines in output. An abstraction away
>> from this so that any ratio of "yes" to "no" lines could be printed while
>> keeping the order of the original lines would be great.
>>
>
> Please show us what code you have written, and in what way it fails to meet
> your expectations.
>
> Your specification is IMHO a nice piece of pseudocode which could translate
> to Python fairly easily!
>
> What do we do at steps 4ff if the line does not end in "yes" or "no"?
>
> If you have not written any code make a stab at it. You could start by
> asking "how in Python does one":
> open a file?
> iterate (loop)?
> get the next line from a file?
> test for equality?
> examine the end of a string?
>
>
> --
> Bob Gailer
> Chapel Hill NC
> 919-636-4239
>
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Re: [Tutor] Working with lines from file and printing to another keeping sequential order
Dan Liang wrote: Dear Tutors, I have a file from which I want to extract lines that end in certain strings and print to a second file. More specifically, I want to: 1) iterate over each line in the file, and if it ends in "yes", print it. 2) move to the line following the one described in #1 above, and if it ends in, "no" print it. 3) move to third line, and if it ends in "no", print it. 4) move to fourth line, and if it ends in "no" discard it, but if it ends in "yes" repeat 1, 2, and 3 above. 5) move to fifth line, and if it ends in "no" discard it, but if it ends in "yes" repeat 1, 2, 3, and 4 above, and so on. The goal is to get a ratio of 1 to 2 "yes" to "no" lines from a file in such a way that keeps the order of the lines in output. An abstraction away from this so that any ratio of "yes" to "no" lines could be printed while keeping the order of the original lines would be great. Please show us what code you have written, and in what way it fails to meet your expectations. Your specification is IMHO a nice piece of pseudocode which could translate to Python fairly easily! What do we do at steps 4ff if the line does not end in "yes" or "no"? If you have not written any code make a stab at it. You could start by asking "how in Python does one": open a file? iterate (loop)? get the next line from a file? test for equality? examine the end of a string? -- Bob Gailer Chapel Hill NC 919-636-4239 ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Working with lines from file and printing to another keeping sequential order
Dear Tutors, I have a file from which I want to extract lines that end in certain strings and print to a second file. More specifically, I want to: 1) iterate over each line in the file, and if it ends in "yes", print it. 2) move to the line following the one described in #1 above, and if it ends in, "no" print it. 3) move to third line, and if it ends in "no", print it. 4) move to fourth line, and if it ends in "no" discard it, but if it ends in "yes" repeat 1, 2, and 3 above. 5) move to fifth line, and if it ends in "no" discard it, but if it ends in "yes" repeat 1, 2, 3, and 4 above, and so on. The goal is to get a ratio of 1 to 2 "yes" to "no" lines from a file in such a way that keeps the order of the lines in output. An abstraction away from this so that any ratio of "yes" to "no" lines could be printed while keeping the order of the original lines would be great. I am new to Python and could not solve the problem. Your help is appreciated. Cheers, --dan ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
