Most efficient way to remove specific words from a string

Question

Lets say I have the following string,

ing = "2 cup butter, softened"

and I only want butter from the string (I have done the following so far),

ing.replace('2','').replace('cup','').replace(', ','').replace('softened','')
ing.strip()

EDIT

    Traceback (most recent call last):
  File "parsley.py", line 107, in <module>
    leaf.write_ingredients_to_csv()
  File "parsley.py", line 91, in write_ingredients_to_csv
    out = re.sub(words, '', matched)
  File "C:\Users\Nikhil\Anaconda3\lib\re.py", line 191, in sub
    return _compile(pattern, flags).sub(repl, string, count)
  File "C:\Users\Nikhil\Anaconda3\lib\re.py", line 301, in _compile
    p = sre_compile.compile(pattern, flags)
  File "C:\Users\Nikhil\Anaconda3\lib\sre_compile.py", line 562, in compile
    p = sre_parse.parse(p, flags)
  File "C:\Users\Nikhil\Anaconda3\lib\sre_parse.py", line 855, in parse
    p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, 0)
  File "C:\Users\Nikhil\Anaconda3\lib\sre_parse.py", line 416, in _parse_sub
    not nested and not items))
  File "C:\Users\Nikhil\Anaconda3\lib\sre_parse.py", line 752, in _parse
    len(char) + 1)
sre_constants.error: unknown extension ?| at position 23

Is there a more efficient way of doing this in Python 3? What I have shown is just one example of the string that I am processing. There are many more strings with different words that I need to remove such as cups,cup,tablespoons and teaspoon. I am using the same approach to eliminate the words from the string, so is there a better way of doing this?

so what is the common format of the strings? otherwise you cannot come up with a generic way to deal with all of it — johnII, Jan 20 '18 at 04:58
You may have a look at this: https://stackoverflow.com/questions/25346058/removing-list-of-words-from-a-string — kiner_shah, Jan 20 '18 at 04:59
Or this : https://stackoverflow.com/questions/6116978/how-to-replace-multiple-substrings-of-a-string — Advay Umare, Jan 20 '18 at 05:00
@johnII That's the problem, there is no specific format for the string... — Nikhil Raghavendra, Jan 20 '18 at 05:00
well then for the above only you can use split e.g. ing.split(',')[0].split(' ')[-1] — johnII, Jan 20 '18 at 05:02
The problem is that the recipes are written by different authors who don't have a specific format to follow. That is the reason why it's so problematic... — Nikhil Raghavendra, Jan 20 '18 at 05:04

James · Accepted Answer · 2018-01-20T05:36:29.993

2

You may want to use regular expressions.

import re

words = r'oz|lbs?|cups?|tablespoons?|tea‌spoons?|softened'
words_rm = r'slices?|shredded|sheets?|cans?|\d ?g\b'
other = r'[\d,;#\(\)\[\]\.]'
ing = "2 cup butter, softened"
out = re.sub(words, '', ing)
out = re.sub(words_rm, '', out)
out = re.sub(other, '', out)
out.strip()
# returns:
'butter'

edited Jan 20 '18 at 05:36

answered Jan 20 '18 at 05:02

James

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I get this error, `unknown extension ?| at position 23`. How do I solve it? – Nikhil Raghavendra Jan 20 '18 at 05:18
I would need the full traceback – James Jan 20 '18 at 05:20
What are you using for `words`? – James Jan 20 '18 at 05:27
I am using, `words = r'oz?|lbs?|cups?|lb?|.?|(?|cup?|tablespoons?|tablespoon?|teaspoons?|teaspoon?|)'` and `words_rm = r'slices?|slice?|shredded?|sheets?|sheet?|g ?|cans ?|can'` – Nikhil Raghavendra Jan 20 '18 at 05:30
The period `'.'` is a special character in regex. The way you have it written is an invalid expression. The question mark indicates that the preceeding character is optional. IE: `'cups?'` will match both `'cup'` and `'cups'`. Please see my updated answer. – James Jan 20 '18 at 05:36

Most efficient way to remove specific words from a string

1 Answers1