Replace every instance of a word with another word without breaking other words containing that word

Question

Word, word, word... Sorry for the title.

Let's say I want to replace every instance of "yes" to "no" in a string. I can just use string.replace(). But then there's this problem:

string = "yes eyes yesterday yes"
new_str = string.replace("yes", "no")

# new_str -> "no eno noterday no"

How can I preserve "eyes" and "yesterday" as is, with changing "yes" to "no".

@Paul Collingwood What about when it's in the beginning or the end...? It doesn't work. Edit: or followed by a dot or a comma — UsuallyHelpless, Mar 16 '20 at 15:53
[Python regular expression match whole word](https://stackoverflow.com/q/15863066/1324033) — Sayse, Mar 16 '20 at 15:53
[Replace exact substring in python](https://stackoverflow.com/q/31697043/1324033) — Sayse, Mar 16 '20 at 15:54
it's a start right? :P for homework problems I only give hints. — Paul Collingwood, Mar 16 '20 at 16:29
It's not actually a homework problem... I'm not even learning code in school. Thanks for the effort tho ;) — UsuallyHelpless, Mar 16 '20 at 16:56
Does this answer your question? [Replace exact substring in python](https://stackoverflow.com/questions/31697043/replace-exact-substring-in-python) — AMC, Mar 16 '20 at 20:33
Does this answer your question? [Search and replace with "whole word only" option](https://stackoverflow.com/questions/17730788/search-and-replace-with-whole-word-only-option) — Georgy, Mar 21 '20 at 11:02

score 5 · Answer 1 · answered Mar 16 '20 at 15:55

You can use re here.

re.sub(r'\byes\b','no',"yes eyes yesterday yes")
# 'no eyes yesterday no'

From docs:

\b- Matches the empty string, but only at the beginning or end of a word. A word is defined as a sequence of word characters. Note that formally, \b is defined as the boundary between a \w and a \W character (or vice versa), or between \w and the beginning/end of the string. This means that r'\bfoo\b' matches 'foo', 'foo.', '(foo)', 'bar foo baz' but not 'foobar' or 'foo3'.

score 3 · Answer 2 · answered Mar 16 '20 at 15:56

3

Try this:

import re

string = "yes eyes yesterday yes"
new_str = re.sub(r"\byes\b", "no", string)

Output:

no eyes yesterday no

answered Mar 16 '20 at 15:56

Shubham Sharma

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MarianD · Accepted Answer · 2020-03-16T16:52:40.990

" ".join(["no" if word=="yes" else word for word in string.split()])

'no eyes yesterday no'

The explanation:

First, break the string into a list of individual words:

string.split()

['yes', 'eyes', 'yesterday', 'yes']

Then iterate over this list of individual words and use the expression

"no" if word=="yes" else word

to replace every "yes" with "no" in a list comprehension

["no" if word=="yes" else word for word in string.split()]

['no', 'eyes', 'yesterday', 'no']

Finally, return this changed list back to a string with the .join() method of the string " " (the delimiter).

score 1 · Answer 4 · answered Mar 16 '20 at 15:55

If you use regex, you can specify word boundaries with \b:

import re

sentence = 'yes no yesyes'

sentence = re.sub(r'\byes\b', 'no', sentence)
print(sentence)

Output:

no no yesyes

Notice that 'yesyes' is not changed (to 'no').

You can read more about Python's re module here.

Replace every instance of a word with another word without breaking other words containing that word

4 Answers4