Morning Removing last character

[sumncguy]

I have the need to change a list of ips into a regular expression, then copy / paste the results else where

The starting list

10.10.10.10 host1
10.10.10.11 host2
10.10.10.12 host3
10.10.10.13 host4
10.10.10.14 host5

The desired output

^10.10.10.10$|^10.10.10.11$|^10.10.10.12$|^10.10.10.13$|^10.10.10.14$

The current output .. notice the last "|", I want that removed.

^10.10.10.10$|^10.10.10.11$|^10.10.10.12$|^10.10.10.13$|^10.10.10.14$|

My cheep g code

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!/usr/bin/python # -*- coding: utf-8 -*- from __future__ import print_function import sys, os, re def cls():     os.system('clear')   def main():        cls()        try:           #olist = []           for line in open (sys.argv[1], 'r' ):               word_list = line.split()               word_list[0] = re.sub("^", "^", word_list[0], flags=re.M)               word_list[0] = re.sub("$", "$|", word_list[0], flags=re.M)               print(word_list[0],end='')           print('\n\n')              except IOError as e :            print("File Open Error")            print("Error :", str(e))        except IndexError as i :            print("Usage: argv[0] <file having ip as the first field, hostname as the second>\nExample : 10.10.10.10 host1\n          10.10.10.10 host2\n          10.10.10.12 host3")     main()

Working on a Linux vm

[localhost etc]$ cat system-release
CentOS Linux release 7.6.1810 (Core)

[localhost etc]$ python -V
Python 2.7.5

I know .. the Python version is old and crusty considering 3.8 is in beta ... but they are still using 2.7 at work.

My Question
The only way I can think of to get rid of the trailing pipe is to count the lines in the file, iterate a separate counter as I run through the file, compare the constant to the line counter, if equal do some thing like print word_list[0][:-1]

Is there a better way to do this .. as a side question .. is there a way to combine the 2 re's into a single line ?

Thanks for any help provided !!!

Regards
Sum

[DeaD_EyE]

Use str.join

My output:

Output:
deadeye@nexus ~ $ python2.7 parse_ips.py                                                                                                                                                     
Without piping to program, you have to use --input-file
deadeye@nexus ~ $ python2.7 parse_ips.py --input-file                                                                                                                                        
usage: parse_ips.py [-h] [--input-file INPUT_FILE]
parse_ips.py: error: argument --input-file: expected one argument
deadeye@nexus ~ $ python2.7 parse_ips.py --input-file hosts.txt                                                                                                                              
^10\.10\.10\.10$|^10\.10\.10\.11$|^10\.10\.10\.12$|^10\.10\.10\.13$|^10\.10\.10\.14$                                              
deadeye@nexus ~ $ cat hosts.txt | python2.7 parse_ips.py                                                                                                                                     
^10\.10\.10\.10$|^10\.10\.10\.11$|^10\.10\.10\.12$|^10\.10\.10\.13$|^10\.10\.10\.14$

Code:

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#!/usr/bin/env python2.7 from __future__ import print_function import sys import argparse     def ip2regex(text):     ips = []     for row in text.splitlines():         try:             ip, hostname = row.split()         except ValueError:             # skip errors             continue         ip = '^' + ip.replace('.', r'\.') + '$'         ips.append(ip)     return '|'.join(ips)     if __name__ == '__main__':     parser = argparse.ArgumentParser()     parser.add_argument('--input-file', required=False, help='Input file to generate regex output.')     args = parser.parse_args()     if args.input_file is None and not sys.stdin.isatty():         print(ip2regex(sys.stdin.read()))     elif args.input_file and sys.stdin.isatty():         with open(args.input_file) as fd:             print(ip2regex(fd.read()))     else:         print('Without piping to program, you have to use --input-file', file=sys.stderr)

Line 15-17 preparing the IP address. By the way, a dot is a metachar in regex. The dot stands for any kind of char.

If you use the dot without escaping it, the regex ^10.10.10.10$ will be also match: 10510710310

PS: split is the opposite of join.

[buran]

why complicate things that much? simple string methods and formating would do?

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infile = sys.argv[1] with (infile, 'r') as f:     ips = [ip_addr for line in f for ip_addr, *_ in line.split()] print('|'.join('^{}$'.format(ip_addr) for ip_addr in ips))

and these 4 lines can be shorten to 2

[sumncguy]

Use str.join

My output:

Output:
deadeye@nexus ~ $ python2.7 parse_ips.py                                                                                                                                                     
Without piping to program, you have to use --input-file
deadeye@nexus ~ $ python2.7 parse_ips.py --input-file                                                                                                                                        
usage: parse_ips.py [-h] [--input-file INPUT_FILE]
parse_ips.py: error: argument --input-file: expected one argument
deadeye@nexus ~ $ python2.7 parse_ips.py --input-file hosts.txt                                                                                                                              
^10\.10\.10\.10$|^10\.10\.10\.11$|^10\.10\.10\.12$|^10\.10\.10\.13$|^10\.10\.10\.14$                                              
deadeye@nexus ~ $ cat hosts.txt | python2.7 parse_ips.py                                                                                                                                     
^10\.10\.10\.10$|^10\.10\.10\.11$|^10\.10\.10\.12$|^10\.10\.10\.13$|^10\.10\.10\.14$

Yep thanks .. I understand that he "." means any char. The App Im pasting into recognizes an ip just so long its wrapped in ^$.

Thanks.

Code:

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#!/usr/bin/env python2.7 from __future__ import print_function import sys import argparse     def ip2regex(text):     ips = []     for row in text.splitlines():         try:             ip, hostname = row.split()         except ValueError:             # skip errors             continue         ip = '^' + ip.replace('.', r'\.') + '$'         ips.append(ip)     return '|'.join(ips)     if __name__ == '__main__':     parser = argparse.ArgumentParser()     parser.add_argument('--input-file', required=False, help='Input file to generate regex output.')     args = parser.parse_args()     if args.input_file is None and not sys.stdin.isatty():         print(ip2regex(sys.stdin.read()))     elif args.input_file and sys.stdin.isatty():         with open(args.input_file) as fd:             print(ip2regex(fd.read()))     else:         print('Without piping to program, you have to use --input-file', file=sys.stderr)

Line 15-17 preparing the IP address. By the way, a dot is a metachar in regex. The dot stands for any kind of char.

If you use the dot without escaping it, the regex ^10.10.10.10$ will be also match: 10510710310

PS: split is the opposite of join.

---

Ive seen this construct in some example code .. but not in any instruction .... probably because Im just starting out.

What is it called and where can I learn about it ..

1	ips = [ip_addr for line in f for ip_addr, *_ in line.split()]

[buran]

What is it called and where can I learn about it ..

this is list comprehension. but yu can also have generator expression, e.g. (ip_addr for line in f for ip_addr, *_ in line.split()) in which case it will not create full list in memory or dict comprehension
note that it can be expanded as normal for loop

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infile = sys.argv[1] ips = [] with (infile, 'r') as f:     for line in f:         for ip_addr, *_ in line.split():             ips.append(ip_addr) print('|'.join('^{}$'.format(ip_addr) for ip_addr in ips))

[sumncguy]

list comprehension .. thank you

I dont like to just copy and paste solutions given that I don't understand. Main reason, if I did, next month when I look at the code again ... I'd be thinking 'What the heck does that do again ?" So if I get even a high level understanding an annotate my script .. it will be easier to jar this crusty 54 year old memory ! :)

Thanks
Sum

[DeaD_EyE]

The _ is a valid name in Python.
In interactive mode it holds the last result, if it was not assigned to a name.

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>>> 5+5 10 >>> print(_) 10

And the effect of the wildcard in front of one of the names in a assignment:

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start, *middle, end = 'start 1 2 3 4 5 end'.split() print(start) print(middle) print(end)

Output:
start
['1', '2', '3', '4', '5']
end

1	ips = [ip_addr for line in f for ip_addr, *_ in line.split()]

Is the same like:

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ips = [] for line in f:     for ip_addr, *_ in line.split():        ips.append(ip_addr)

The name f should point to an open file. Iterating over a file-object, gets line by line.
But I think this example is overcomplicated. You can write this as:

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ips = [] for line in f:     ip_addr, *rest = line.split()     ips.append(ip_addr)

Then you get rid of the nested loop.
Turning this into a list comprehension:

1	ips = [line.split()[0] for line in f]

[sumncguy]

I found that a few VMs are using 2.6.6..

Seems that format wasnt introduced until 2.7 .. so the print solution doesnt work in some cases.

Can anyone point me to a place where I can find out how to truncate the last "|" in 2.6.6.

I wish
1. they would standardize the Linux and python version they are using.
2. upgrade at least to python 3.x .. especially being that 3.8 is in beta 2 !!

I work for a big company .. cant say which .. but I find it incredible that they arent really doing any admin on their VMs.

Thanks for the help
Sum

[buran]

it works, in 2.6 just need to number the placehodler(s) (i.e. explicitly specify the order in which to place values in palceholders).

1	print('|'.join('^{0}$'.format(ip_addr) for ip_addr in ips))

this will work also in 2.7 and 3.x versions
Or to say it the other way around - in 2.7 and 3.x you can skip the number