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Python DNA sequence slice gives \N as wrong content in slice result

I am surprising, I am using python to slice a long DNA Sequence (4699673 character)to a specific length supstring, it's working properly with a problem in result, after 71 good result \n start apear in result for few slices then correct slices again and so on for whole long file
the code:
import sys
filename = open("out_filePU.txt",'w')
sys.stdout = filename
my_file = open("GCF_000005845.2_ASM584v2_genomic_edited.fna")
st = my_file.read()
length = len(st)
print ( 'Sequence Length is, :' ,length)
for i in range(0,len(st[:-9])):
print(st[i:i+9], i)
figure shows the error from the result file
please i need advice on that.

Your sequence file contains multiple lines, and at the end of each line there is a line break \n. You can remove them with st = my_file.read().replace("\n", "").

Try st = re.sub('\\s', '', my_file.read()) to replace any newlines or other whitespace (you'll need to add import re at the top of your script).
Then for i in range(0,len(st[:-9]),9): to step through your data in increments of nine characters. Otherwise you're only advancing by one character each time: that's why you can see the diagonal patterns in your output.

Parsing numbers in strings from a file

I have a txt file as here:
pid,party,state,res
SC5,Republican,NY,Donald Trump 45%-Marco Rubio 18%-John Kasich 18%-Ted Cruz 11%
TB1,Republican,AR,Ted Cruz 27%-Marco Rubio 23%-Donald Trump 23%-Ben Carson 11%
FX2,Democratic,MI,Hillary Clinton 61%-Bernie Sanders 34%
BN1,Democratic,FL,Hillary Clinton 61%-Bernie Sanders 30%
PB2,Democratic,OH,Hillary Clinton 56%-Bernie Sanders 35%
what I want to do, is check that the % of each "res" gets to 100%
def addPoll(pid,party,state,res,filetype):
with open('Polls.txt', 'a+') as file: # open file temporarly for writing and reading
lines = file.readlines() # get all lines from file
file.seek(0)
next(file) # go to next line --
#this is suppose to skip the 1st line with pid/pary/state/res
for line in lines: # loop
line = line.split(',', 3)[3]
y = line.split()
print y
#else:
#file.write(pid + "," + party + "," + state + "," + res+"\n")
#file.close()
return "pass"
print addPoll("123","Democratic","OH","bla bla 50%-Asd ASD 50%",'f')
So in my code I manage to split the last ',' and enter it into a list, but im not sure how I can get only the numbers out of that text.

You can use regex to find all the numbers:
import re
for line in lines:
numbers = re.findall(r'\d+', line)
numbers = [int(n) for n in numbers]
print(sum(numbers))
This will print
0 # no numbers in the first line
97
85
97
92
93
The re.findall() method finds all substrings matching the specified pattern, which in this case is \d+, meaning any continuous string of digits. This returns a list of strings, which we cast to a list of ints, then take the sum.

It seems like what you have is CSV. Instead of trying to parse that on your own, Python already has a builtin parser that will give you back nice dictionaries (so you can do line['res']):
import csv
with open('Polls.txt') as f:
reader = csv.DictReader(f)
for row in reader:
# Do something with row['res']
pass
For the # Do something part, you can either parse the field manually (it appears to be structured): split('-') and then rsplit(' ', 1) each - separated part (the last thing should be the percent). If you're trying to enforce a format, then I'd definitely go this route, but regex are also a fine solution too for quickly pulling out what you want. You'll want to read up on them, but in your case, you want \d+%:
# Manually parse (throws IndexError if there isn't a space separating candidate name and %)
percents = [candidate.rsplit(' ', 1)[1] for candidate row['res'].split('-')]
if not all(p.endswith('%') for p in percents):
# Handle bad percent (not ending in %)
pass
else:
# Throws ValueError if any of the percents aren't integers
percents = [int(p[:-1]) for p in percents]
if sum(percents) != 100:
# Handle bad total
pass
Or with regex:
percents = [int(match.group(1)) for match in re.finditer(r'(\d+)%', row['res'])]
if sum(percents) != 100:
# Handle bad total here
pass
Regex is certainly shorter, but the former will enforce more strict formatting requirements on row['res'] and will allow you to later extract things like candidate names.
Also some random notes:
You don't need to open with 'a+' unless you plan to append to the file, 'r' will do (and 'r' is implicit, so you don't have to specify it).
Instead of next() use a for loop!

regular expressions in python using quotes

I am attempting to create a regular expression pattern for strings similar to the below which are stored in a file. The aim is to get any column for any row, the rows need not be on a single line. So for example, consider the following file:
"column1a","column2a","column
3a,", #entity 1
"column\"this is, a test\"4a"
"column1b","colu
mn2b,","column3b", #entity 2
"column\"this is, a test\"4b"
"column1c,","column2c","column3c", #entity 3
"column\"this is, a test\"4c"
Each entity consists of four columns, column 4 for entity 2 would be "column\"this is, a test\"4b", column 2 for entity 3 would be "column2c". Each column begins with a quote and closes with a quote, however you must be careful because some columns have escaped quotes. Thanks in advance!

You could do like this, ie
Read the whole file.
Split the input according to the newline character which was not preceded by a comma.
Iterate over the spitted elements and again do splitting on the comma (and also the following optional newline character) which was preceded and followed by double quotes.
Code:
import re
with open(file) as f:
fil = f.read()
m = re.split(r'(?<!,)\n', fil.strip())
for i in m:
print(re.split('(?<="),\n?(?=")', i))
Output:
['"column1a"', '"column2a"', '"column3a,"', '"column\\"this is, a test\\"4a"']
['"column1b"', '"column2b,"', '"column3b"', '"column\\"this is, a test\\"4b"']
['"column1c,"', '"column2c"', '"column3c"', '"column\\"this is, a test\\"4c"']
Here is the check..
$ cat f
"column1a","column2a","column3a,",
"column\"this is, a test\"4a"
"column1b","column2b,","column3b",
"column\"this is, a test\"4b"
"column1c,","column2c","column3c",
"column\"this is, a test\"4c"
$ python3 f.py
['"column1a"', '"column2a"', '"column3a,"', '"column\\"this is, a test\\"4a"']
['"column1b"', '"column2b,"', '"column3b"', '"column\\"this is, a test\\"4b"']
['"column1c,"', '"column2c"', '"column3c"', '"column\\"this is, a test\\"4c"']
f is the input file name and f.py is the file-name which contains the python script.

Your problem is terribly familiar to what I have to deal thrice every month :) Except I'm not using python to solve it, but I can 'translate' what I usually do:
text = r'''"column1a","column2a","column
3a,",
"column\"this is, a test\"4a"
"column1a2","column2a2","column3a2","column4a2"
"column1b","colu
mn2b,","column3b",
"column\"this is, a test\"4b"
"column1c,","column2c","column3c",
"column\"this is, a test\"4c"'''
import re
# Number of columns one line is supposed to have
columns = 4
# Temporary variable to hold partial lines
buffer = ""
# Our regex to check for each column
check = re.compile(r'"(?:[^"\\]*|\\.)*"')
# Read the file line by line
for line in text.split("\n"):
# If there's no stored partial line, this is a new line
if buffer == "":
# Check if we get 4 columns and print, if not, put the line
# into buffer so we store a partial line for later
if len(check.findall(line)) == columns:
print matches
else:
# use line.strip() if you need to trim whitespaces
buffer = line
else:
# Update the variable (containing a partial line) with the
# next line and recheck if we get 4 columns
# use line.strip() if you need to trim whitespaces
buffer = buffer + line
# If we indeed get 4, our line is complete and print
# We must not forget to empty buffer now that we got a whole line
if len(check.findall(buffer)) == columns:
print matches
buffer = ""
# Optional; always good to have a safety backdoor though
# If there is a problem with the csv itself like a weird unescaped
# quote, you send it somewhere else
elif len(check.findall(buffer)) > columns:
print "Error: cannot parse line:\n" + buffer
buffer = ""
ideone demo

matching and dispalying specific lines through python

I have 15 lines in a log file and i want to read the 4th and 10 th line for example through python and display them on output saying this string is found :
abc
def
aaa
aaa
aasd
dsfsfs
dssfsd
sdfsds
sfdsf
ssddfs
sdsf
f
dsf
s
d
please suggest through code how to achieve this in python .
just to elaborate more on this example the first (string or line is unique) and can be found easily in logfile the next String B comes within 40 lines of the first one but this one occurs at lots of places in the log file so i need to read this string withing the first 40 lines after reading string A and print the same that these strings were found.
Also I cant use with command of python as this gives me errors like 'with' will become a reserved keyword in Python 2.6. I am using Python 2.5

You can use this:
fp = open("file")
for i, line in enumerate(fp):
if i == 3:
print line
elif i == 9:
print line
break
fp.close()

def bar(start,end,search_term):
with open("foo.txt") as fil:
if search_term in fil.readlines()[start,end]:
print search_term + " has found"
>>>bar(4, 10, "dsfsfs")
"dsfsfs has found"

#list of random characters
from random import randint
a = list(chr(randint(0,100)) for x in xrange(100))
#look for this
lookfor = 'b'
for element in xrange(100):
if lookfor==a[element]:
print a[element],'on',element
#b on 33
#b on 34
is one easy to read and simple way to do it. Can you give part of your log file as an example? There are other ways that may work better :).
after edits by author:
The easiest thing you can do then is:
looking_for = 'findthis' i = 1 for line in open('filename.txt','r'):
if looking_for == line:
print i, line
i+=1
it's efficient and easy :)

Bash or Python to go backwards?

I have a text file which a lot of random occurrences of the string #STRING_A, and I would be interested in writing a short script which removes only some of them. Particularly one that scans the file and once it finds a line which starts with this string like
#STRING_A
then checks if 3 lines backwards there is another occurrence of a line starting with the same string, like
#STRING_A
#STRING_A
and if it happens, to delete the occurrence 3 lines backward. I was thinking about bash, but I do not know how to "go backwards" with it. So I am sure that this is not possible with bash. I also thought about python, but then I should store all information in memory in order to go backwards and then, for long files it would be unfeasible.
What do you think? Is it possible to do it in bash or python?
Thanks

Funny that after all these hours nobody's yet given a solution to the problem as actually phrased (as #John Machin points out in a comment) -- remove just the leading marker (if followed by another such marker 3 lines down), not the whole line containing it. It's not hard, of course -- here's a tiny mod as needed of #truppo's fun solution, for example:
from itertools import izip, chain
f = "foo.txt"
for third, line in izip(chain(" ", open(f)), open(f)):
if third.startswith("#STRING_A") and line.startswith("#STRING_A"):
line = line[len("#STRING_A"):]
print line,
Of course, in real life, one would use an iterator.tee instead of reading the file twice, have this code in a function, not repeat the marker constant endlessly, &c;-).

Of course Python will work as well. Simply store the last three lines in an array and check if the first element in the array is the same as the value you are currently reading. Then delete the value and print out the current array. You would then move over your elements to make room for the new value and repeat. Of course when the array is filled you'd have to make sure to continue to move values out of the array and put in the newly read values, stopping to check each time to see if the first value in the array matches the value you are currently reading.

Here is a more fun solution, using two iterators with a three element offset :)
from itertools import izip, chain, tee
f1, f2 = tee(open("foo.txt"))
for third, line in izip(chain(" ", f1), f2):
if not (third.startswith("#STRING_A") and line.startswith("#STRING_A")):
print line,

Why shouldn't it possible in bash? You don't need to keep the whole file in memory, just the last three lines (if I understood correctly), and write what's appropriate to standard-out. Redirect that into a temporary file, check that everything worked as expected, and overwrite the source file with the temporary one.
Same goes for Python.
I'd provide a script of my own, but that wouldn't be tested. ;-)

As AlbertoPL said, store lines in a fifo for later use--don't "go backwards". For this I would definitely use python over bash+sed/awk/whatever.
I took a few moments to code this snippet up:
from collections import deque
line_fifo = deque()
for line in open("test"):
line_fifo.append(line)
if len(line_fifo) == 4:
# "look 3 lines backward"
if line_fifo[0] == line_fifo[-1] == "#STRING_A\n":
# get rid of that match
line_fifo.popleft()
else:
# print out the top of the fifo
print line_fifo.popleft(),
# don't forget to print out the fifo when the file ends
for line in line_fifo: print line,

This code will scan through the file, and remove lines starting with the marker. It only keeps only three lines in memory by default:
from collections import deque
def delete(fp, marker, gap=3):
"""Delete lines from *fp* if they with *marker* and are followed
by another line starting with *marker* *gap* lines after.
"""
buf = deque()
for line in fp:
if len(buf) < gap:
buf.append(line)
else:
old = buf.popleft()
if not (line.startswith(marker) and old.startswith(marker)):
yield old
buf.append(line)
for line in buf:
yield line
I've tested it with:
>>> from StringIO import StringIO
>>> fp = StringIO('''a
... b
... xxx 1
... c
... xxx 2
... d
... e
... xxx 3
... f
... g
... h
... xxx 4
... i''')
>>> print ''.join(delete(fp, 'xxx'))
a
b
xxx 1
c
d
e
xxx 3
f
g
h
xxx 4
i

This "answer" is for lyrae ... I'll amend my previous comment: if the needle is in the first 3 lines of the file, your script will either cause an IndexError or access a line that it shouldn't be accessing, sometimes with interesting side-effects.
Example of your script causing IndexError:
>>> lines = "#string line 0\nblah blah\n".splitlines(True)
>>> needle = "#string "
>>> for i,line in enumerate(lines):
... if line.startswith(needle) and lines[i-3].startswith(needle):
... lines[i-3] = lines[i-3].replace(needle, "")
...
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
IndexError: list index out of range
and this example shows not only that the Earth is round but also why your "fix" to the "don't delete the whole line" problem should have used .replace(needle, "", 1) or [len(needle):] instead of .replace(needle, "")
>>> lines = "NEEDLE x NEEDLE y\nnoddle\nnuddle\n".splitlines(True)
>>> needle = "NEEDLE"
>>> # Expected result: no change to the file
... for i,line in enumerate(lines):
... if line.startswith(needle) and lines[i-3].startswith(needle):
... lines[i-3] = lines[i-3].replace(needle, "")
...
>>> print ''.join(lines)
x y <<<=== whoops!
noddle
nuddle
<<<=== still got unwanted newline in here
>>>

My awk-fu has never been that good... but the following may provide you what you're looking for in a bash-shell/shell-utility form:
sed `awk 'BEGIN{ORS=";"}
/#STRING_A/ {
if(LAST!="" && LAST+3 >= NR) print LAST "d"
LAST = NR
}' test_file` test_file
Basically... awk is producing a command for sed to strip certain lines. I'm sure there's a relatively easy way to make awk do all of the processing, but this does seem to work.
The bad part? It does read the test_file twice.
The good part? It is a bash/shell-utility implementation.
Edit: Alex Martelli points out that the sample file above might have confused me. (my above code deletes the whole line, rather than the #STRING_A flag only)
This is easily remedied by adjusting the command to sed:
sed `awk 'BEGIN{ORS=";"}
/#STRING_A/ {
if(LAST!="" && LAST+3 >= NR) print LAST "s/#STRING_A//"
LAST = NR
}' test_file` test_file

This may be what you're looking for?
lines = open('sample.txt').readlines()
needle = "#string "
for i,line in enumerate(lines):
if line.startswith(needle) and lines[i-3].startswith(needle):
lines[i-3] = lines[i-3].replace(needle, "")
print ''.join(lines)
this outputs:
string 0 extra text
string 1 extra text
string 2 extra text
string 3 extra text
--replaced -- 4 extra text
string 5 extra text
string 6 extra text
#string 7 extra text
string 8 extra text
string 9 extra text
string 10 extra text

In bash you can use sort -r filename and tail -n filename to read the file backwards.
$LINES=`tail -n filename | sort -r`
# now iterate through the lines and do your checking

I would consider using sed. gnu sed supports definition of line ranges. if sed would fail, then there is another beast - awk and I'm sure you can do it with awk.
O.K. I feel I should put my awk POC. I could not figure out to use sed addresses. I have not tried combination of awk+sed, but it seems to me it's overkill.
my awk script works as follows:
It reads lines and stores them into 3 line buffer
once desired pattern is found (/^data.*/ in my case), the 3-line buffer is looked up to check, whether desired pattern has been seen three lines ago
if pattern has been seen, then 3 lines are scratched
to be honest, I would probably go with python also, given that awk is really awkward.
the AWK code follows:
function max(a, b)
{
if (a > b)
return a;
else
return b;
}
BEGIN {
w = 0; #write index
r = 0; #read index
buf[0, 1, 2]; #buffer
}
END {
# flush buffer
# start at read index and print out up to w index
for (k = r % 3; k r - max(r - 3, 0); k--) {
#search in 3 line history buf
if (match(buf[k % 3], /^data.*/) != 0) {
# found -> remove lines from history
# by rewriting them -> adjust write index
w -= max(r, 3);
}
}
buf[w % 3] = $0;
w++;
}
/^.*/ {
# store line into buffer, if the history
# is full, print out the oldest one.
if (w > 2) {
print buf[r % 3];
r++;
buf[w % 3] = $0;
}
else {
buf[w] = $0;
}
w++;
}