Print Lines Containing String: Odd Behavior

Question

I am using Python3 to try to emulate

awk '/STRING/'

I made some code that works, but it stops on the first instance instead of finding all lines that contain the specified character/string.

After I made the code, I saw these two pages, but the suggestions did not work

Print line containing "word" python

Search and get a line in Python

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#Made by Devyn Collier Johnson, NCLA, Linux+, LPIC-1, DCTS
def cat(openfile): #Emulates cat#
    with open(openfile) as file:
        lines = file.readlines()
        return ''.join(lines)
def GETLINEWITH(FILECONTENTS, CONTAINING):
    for item in FILECONTENTS.split('\n'):
        if CONTAINING in item:
            return item.strip()

print(GETLINEWITH(cat('./Base.xaiml'), 'terminal'))

I have a file (./Base.xaiml) that contains several instances of the word "terminal". I am using this file and string for testing purposes.

EDIT: I also want to save the results to a variable -

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#Made by Devyn Collier Johnson, NCLA, Linux+, LPIC-1, DCTS
def cat(openfile): #Emulates cat#
    with open(openfile) as file:
        lines = file.readlines()
        return ''.join(lines)
def GETLINEWITH(FILECONTENTS, CONTAINING):
    for item in FILECONTENTS.split('\n'):
        if CONTAINING in item:
            print(item.strip()) #I implemented the give suggestion

VAR = GETLINEWITH(cat('./Base.xaiml'), 'terminal'))

Results:

I tried Jon Clements suggestion:

with open('./Base.xaiml') as fin:
    matching = ('terminal' in line for line in fin)
    for line in matching:
        VAR = matching
print(VAR)

However, the output is one memory address. ''.join() and group() do not help.

Edit2:

Newest code Issues - nonetype error and the output cannot be saved to a variable

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#Made by Devyn Collier Johnson, NCLA, Linux+, LPIC-1, DCTS
def cat(openfile): #Emulates cat#
    with open(openfile) as file:
        lines = file.readlines()
        return ''.join(lines)
def GETLINEWITH(FILECONTENTS, CONTAINING):
    for item in FILECONTENTS.split('\n'):
        if CONTAINING in item:
            print(item.strip())
for line in GETLINEWITH(cat('./Base.xaiml'), 'terminal'):
    print(line)

`cat` does more than read a file. It's about con*cat*enating lines. — wim, Dec 06 '13 at 14:34
The answers you linked have working solutions - why are you not just using one of those that will solve this ? — Jon Clements, Dec 06 '13 at 14:35
The answers in those question works if you change `print x` to `print(x)`. Your complicated "read-split-paste-split-search" logic is unnecessary. — Fred Foo, Dec 06 '13 at 14:37
By the way there is no point to `.readlines()` and then `''.join(lines)` immediately after. That's the same as just `.read()` — wim, Dec 06 '13 at 14:38
@wim I know, but that is the name I choose since it resembles cat. — Devyn Collier Johnson, Dec 06 '13 at 14:43
Did you see the `list=` line I posted... that'll generate a list of all the matches... All you've done is loop over the matches and assign it to `VAR` each time, so you'll end up with the last one... — Jon Clements, Dec 06 '13 at 15:03
@JonClements I am wanting to save the plain text to a variable. — Devyn Collier Johnson, Dec 06 '13 at 15:05
@JonClements Notice that I said I wanted to emulate that specific awk command. — Devyn Collier Johnson, Dec 06 '13 at 15:06
@DevynCollierJohnson sorry - brain burp - changed the generator expression to return the lines, not a boolean if something is in the line — Jon Clements, Dec 06 '13 at 15:07
@JonClements Okay, "return" only works in functions (return not in function error). I have my newest code under "Edit2". I get some "NoneType" error and the output will not save to a variable. — Devyn Collier Johnson, Dec 06 '13 at 15:22
@DevynCollierJohnson because you're printing it in the function, and not returning anything so it implicitly returns `None`.... why are you not using `yield` as I suggested? — Jon Clements, Dec 06 '13 at 15:28

casey · Accepted Answer · 2013-12-06T16:57:47.580

Here you go, note that I am just putting together everyone elses comments explicitly for you.

#!/usr/bin/env python3

def cat(openfile):
  with open(openfile) as file:
    return file.read()

def GETLINEWITH(FILECONTENTS, CONTAINING):
  for item in FILECONTENTS.split('\n'):
    if CONTAINING in item:
      yield item.strip()

matchedlines = []

for line in GETLINEWITH(cat('./Base.xaiml'), 'terminal'):
   print(line)
   matchedlines.append(line)

print(matchedlines)

The matchedlines variable is just an example for you of one way to save the matched lines in a variable.

An alternative GETLINEWITH implementation is:

import re

def GETLINEWITH(FILECONTENTS, CONTAINING):
  for item in FILECONTENTS.split('\n'):
    m = re.search(CONTAINING, item)
    if m:
      yield m.string

Which will let you match on regular expressions.

Thank you. I like how you put it all together for me. – Devyn Collier Johnson Dec 06 '13 at 19:22 — Devyn Collier Johnson, Dec 06 '13 at 19:22

Jon Clements · Answer 2 · 2013-12-06T15:06:53.143

1

Anyway - the reason it "stops" is because you're returning after a match....

def GETLINEWITH(FILECONTENTS, CONTAINING):
    for item in FILECONTENTS.split('\n'):
        if CONTAINING in item:
            return item.strip() # <---- returns as soon as something's found

Change it to a yield to make the function a generator and then loop over it:

for line in GETLINEWITH(cat('./Base.xaiml'), 'terminal'):
    print(line)

Ultimately, your function should just be:

with open('thefile') as fin:
    matching = (line for line in fin if 'something' in line)
    for line in matching:
        # do something

Or, put them all into a list:

lines = list(matching)

edited Dec 06 '13 at 15:06

answered Dec 06 '13 at 14:38

Jon Clements

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Thanks, but how would I save this to a variable? If I change the code to save this as a variable, the results are printed to the screen. – Devyn Collier Johnson Dec 06 '13 at 14:43
@DevynCollierJohnson made a couple of edits... does that answer your question? – Jon Clements Dec 06 '13 at 14:45
Jon, I tried your idea. See my edit for the results. Close, but not quite. Thanks for your efforts. – Devyn Collier Johnson Dec 06 '13 at 14:56
Thanks Jon for all of the help and sorry for any inconvenience. – Devyn Collier Johnson Dec 06 '13 at 19:22

Marc Poulin · Answer 3 · 2013-12-06T17:56:33.467

File objects are iterable, and a list comprehension can be used to filter the input.

with open('./Base.xaiml','r') as lines:
    matching_lines = [ line.rstrip('\n')
                       for line in lines
                       if line.find('terminal') != -1 ]

for line in matching_lines:
    print line         # change to print(line) for python 3.x

EDIT: or if you really want it to be a function

def matching_lines(filename, substring):
    """ Return all the lines in a file that contain a given substring. """
    with open(filename,'r') as f:
        return [s.rstrip('\n') for s in f if s.find(substring) != -1]

for s in matching_lines('./Base.xaiml', 'terminal'):
    print s

Print Lines Containing String: Odd Behavior

3 Answers3