Develop Reference

Process each line of text file using Python

I am fairly new to Python. I have a text file containing many blocks of data in following format along with other unnecessary blocks.
NOT REQUIRED :: 123
Connected Part-1:: A ~$
Connected Part-3:: B ~$
Connector Location:: 100 200 300 ~$
NOT REQUIRED :: 456
Connected Part-2:: C ~$
i wish to extract the info (A,B,C, 100 200 300) corresponding to each property ( connected part-1, Connector location) and store it as list to use it later. I have prepared following code which reads file, cleans the line and store it as list.
import fileinput
with open('C:/Users/file.txt') as f:
content = f.readlines()
for line in content:
if 'Connected Part-1' in line or 'Connected Part-3' in line:
if 'Connected Part-1' in line:
connected_part_1 = [s.strip(' \n ~ $ Connected Part -1 ::') for s in content]
print ('PART_1:',connected_part_1)
if 'Connected Part-3' in line:
connected_part_3 = [s.strip(' \n ~ $ Connected Part -3 ::') for s in content]
print ('PART_3:',connected_part_3)
if 'Connector Location' in line:
# removing unwanted characters and converting into the list
content_clean_1 = [s.strip('\n ~ $ Connector Location::') for s in content]
#converting a single string item in list to a string
s = " ".join(content_clean_1)
# splitting the string and converting into a list
weld_location= s.split(" ")
print ('POSITION',weld_location)
here is the output
PART_1: ['A', '\t\tConnector Location:: 100.00 200.00 300.00', '\t\tConnected Part-3:: C~\t']
POSITION ['d', 'Part-1::', 'A', '\t\tConnector', 'Location::', '100.00', '200.00', '300.00', '\t\tConnected', 'Part-3::', 'C~\t']
PART_3: ['1:: A', '\t\tConnector Location:: 100.00 200.00 300.00', '\t\tConnected Part-3:: C~\t']
From the output of this program, i may conclude that, since 'content' is the string consisting all the characters in the file, the program is not reading an individual line. Instead it is considering all text as single string. Could anyone please help in this case?
I am expecting following output:
PART_1: ['A']
PART_3: ['C']
POSITION: ['100.00', '200.00','300.00']
(Note) When i am using individual files containing single line of data, it works fine. Sorry for such a long question

I will try to make it clear, and show how I would do it without regex. First of all, the biggest issue with the code presented is that when using the string.strip function the entire content list is being read:
connected_part_1 = [s.strip(' \n ~ $ Connected Part -1 ::') for s in content]
Content is the entire file lines, I think you want simply something like:
connected_part_1 = [line.strip(' \n ~ $ Connected Part -1 ::')]
How to parse the file is a bit subjective, but given the file format posted as input, I would do it like this:
templatestr = "{}: {}"
with open('inputreadlines.txt') as f:
content = f.readlines()
for line in content:
label, value = line.split('::')
ltokens = label.split()
if ltokens[0] == 'Connected':
print(templatestr.format(
ltokens[-1], #The last word on the label
value.split()[:-1])) #the split value without the last word '~$'
elif ltokens[0] == 'Connector':
print(value.split()[:-1]) #the split value without the last word '~$'
else: #NOT REQUIRED
pass
You can use the string.strip function to remove the funny characters '~$' instead of removing the last token as in the example.

Increase String by Sequential Index

In a file dealing with climatological variables involving a running mean with hours, the hours progress in sequence.
Is there a sed/awk command that would take that hour (string) in the file and then change it by two, so next time the file is read its (202) and so on to (204) etc...
See the number being added to 'i' below.
timeprime = i + 569
'define climomslp = prmslmsl(t = 'timeprime' )
My goal is to increase the number in this case, 569, by one each time the file runs through other commands involved in processing the data.
The next desired number next to i would be
timeprime = i + 570 (where 569 is increased by one)
after that...
timeprime = i + 571 (where 570 is increased by one)
If there isn't a sed/awk command to do such a thing, is there such a thing in any other method?
Thank you for any answers.

You can definitely do this in Python (or Perl, Ruby, or whatever other scripting language you like, but you included a Python tag). For example:
#!/usr/bin/env python
import re
import sys
def replace(m):
return '{}{}'.format(m.group(1), int(m.group(2))+2)
for line in sys.stdin:
sys.stdout.write(re.sub(r'(timeprime = i \+ )(\d+)', replace, line))
Hopefully the regex itself is trivial to understand:
(timeprime = i \+ )(\d+)
Debuggex Demo
The sub function can take a to be applied to the match object instead of a string as the "replacement". So, lines that don't match will be printed unchanged; lines that do will have the match substituted for the same two parts, but with the second part replaced by int(number)+2

Here is an alternative using awk:
awk '/^timeprime = i [+]/{$5+=2} 1' file
Starting with this file:
$ cat file
timeprime = i + 569
'define climomslp = prmslmsl(t = 'timeprime' )
We can use the awk command to create a new file:
$ awk '/^timeprime = i [+]/{$5+=2} 1' file
timeprime = i + 571
'define climomslp = prmslmsl(t = 'timeprime' )
To overwrite the original file with the new one, use:
awk '/^timeprime = i [+]/{$5+=2} 1' file >file.tmp && mv file.tmp file
How it works
/^timeprime = i [+]/{$5+=2}
This looks for lines that start with ^timeprime = i + and, on those lines, the fifth field is incremented by 2.
1
This is awk's cryptic shorthand for print the line.

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

Extracting Data from Multiple TXT Files and Creating a Summary CSV File in Python

I have a folder with about 50 .txt files containing data in the following format.
=== Predictions on test data ===
inst# actual predicted error distribution (OFTd1_OF_Latency)
1 1:S 2:R + 0.125,*0.875 (73.84)
I need to write a program that combines the following: my index number (i), the letter of the true class (R or S), the letter of the predicted class, and each of the distribution predictions (the decimals less than 1.0).
I would like it to look like the following when finished, but preferably as a .csv file.
ID True Pred S R
1 S R 0.125 0.875
2 R R 0.105 0.895
3 S S 0.945 0.055
. . . . .
. . . . .
. . . . .
n S S 0.900 0.100
I'm a beginner and a bit fuzzy on how to get all of that parsed and then concatenated and appended. Here's what I was thinking, but feel free to suggest another direction if that would be easier.
for i in range(1, n):
s = str(i)
readin = open('mydata/output/output'+s+'out','r')
#The files are all named the same but with different numbers associated
output = open("mydata/summary.csv", "a")
storage = []
for line in readin:
#data extraction/concatenation here
if line.startswith('1'):
id = i
true = # split at the ':' and take the letter after it
pred = # split at the second ':' and take the letter after it
#some have error '+'s and some don't so I'm not exactly sure what to do to get the distributions
ds = # split at the ',' and take the string of 5 digits before it
if pred == 'R':
dr = #skip the character after the comma but take the have characters after
else:
#take the five characters after the comma
lineholder = id+' , '+true+' , '+pred+' , '+ds+' , '+dr
else: continue
output.write(lineholder)
I think using the indexes would be another option, but it might complicate things if the spacing is off in any of the files and I haven't checked this for sure.
Thank you for your help!

Well first of all, if you want to use CSV, you should use CSV module that comes with python. More about this module here: https://docs.python.org/2.7/library/csv.html I won't demonstrate how to use it, because it's pretty simple.
As for reading the input data, here's my suggestion how to break down every line of the data itself. I assume that lines of data in the input file have their values separated by spaces, and each value cannot contain a space:
def process_line(id_, line):
pieces = line.split() # Now we have an array of values
true = pieces[1].split(':')[1] # split at the ':' and take the letter after it
pred = pieces[2].split(':')[1] # split at the second ':' and take the letter after it
if len(pieces) == 6: # There was an error, the + is there
p4 = pieces[4]
else: # There was no '+' only spaces
p4 = pieces[3]
ds = p4.split(',')[0] # split at the ',' and take the string of 5 digits before it
if pred == 'R':
dr = p4.split(',')[0][1:] #skip the character after the comma but take the have??? characters after
else:
dr = p4.split(',')[0]
return id_+' , '+true+' , '+pred+' , '+ds+' , '+dr
What I mainly used here was split function of strings: https://docs.python.org/2/library/stdtypes.html#str.split and in one place this simple syntax of str[1:] to skip the first character of the string (strings are arrays after all, we can use this slicing syntax).
Keep in mind that my function won't handle any errors or lines formated differently than the one you posted as an example. If the values in every line are separated by tabs and not spaces you should replace this line: pieces = line.split() with pieces = line.split('\t').

i think u can separte floats and then combine it with the strings with the help of re module as follows:
import re
file = open('sample.txt','r')
strings=[[num for num in re.findall(r'\d+\.+\d+',i) for i in file.readlines()]]
print (strings)
file.close()
file = open('sample.txt','r')
num=[[num for num in re.findall(r'\w+\:+\w+',i) for i in file.readlines()]]
print (num)
s= num+strings
print s #[['1:S','2:R'],['0.125','0.875','73.84']] output of the code
this prog is written for one line u can use it for multiple line as well but u need to use a loop for that
contents of sample.txt:
1 1:S 2:R + 0.125,*0.875 (73.84)
2 1:S 2:R + 0.15,*0.85 (69.4)
when you run the prog the result will be:
[['1:S,'2:R'],['1:S','2:R'],['0.125','0.875','73.84'],['0.15,'0.85,'69.4']]
simply concatenate them

This uses regular expressions and the CSV module.
import re
import csv
matcher = re.compile(r'[[:blank:]]*1.*:(.).*:(.).* ([^ ]*),[^0-9]?(.*) ')
filenametemplate = 'mydata/output/output%iout'
output = csv.writer(open('mydata/summary.csv', 'w'))
for i in range(1, n):
for line in open(filenametemplate % i):
m = matcher.match(line)
if m:
output.write([i] + list(m.groups()))

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++;
}