Python Find entire word in string using regex and user input

Question

I'm trying to find the entire word exactly using regex but have the word i'm searching for be a variable value coming from user input. I've tried this:

regex = r"\b(?=\w)" + re.escape(user_input) + r"\b"
if re.match(regex, string_to_search[i], re.IGNORECASE):
      <some code>...

but it matches every occurrence of the string. It matches "var"->"var" which is correct but also matches "var"->"var"iable and I only want it to match "var"->"var" or "string"->"string"

Input: "sword"

String_to_search = "There once was a swordsmith that made a sword"

Desired output: Match "sword" to "sword" and not "swordsmith"

Well, \bvar\b cannot match var in variable. Why are you using re.match? If you want to match user input as a whole string, you may use regex = '{}$'.format(re.escape(user_input)) and then use re.match(). Else, if you need to really just find var as a whole word inside a larger string, you will need re.search with \bvar\b regex. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 15, 2017 at 15:52
Doesn't python have a non regex function like a substring search ? — user557597
– user557597, Commented Aug 15, 2017 at 15:52
If python supported conditionals you could wrap it into conditional boundary's (?(?=\w)\b)(?: your literal )(?(?<=\w)\b) And this \b(?=\w) forces the literal to start with a \w — user557597
– user557597, Commented Aug 15, 2017 at 15:58
@sln yeah but it will find any substring including "var" in variable which i don't want. I'm going to try the .format or re.search and conditional — E. Oregel
– E. Oregel, Commented Aug 15, 2017 at 16:06

Wiktor Stribiżew · Accepted Answer · 2017-08-15 16:54:57Z

3

You seem you want to use a pattern that matches an entire string. Note that \b word boundary is needed when you wan to find partial matches. When you need a full string match, you need anchors. Since re.match anchors the match at the start of string, all you need is $ (end of string position) at the end of the pattern:

regex = '{}$'.format(re.escape(user_input))

and then use

re.match(regex, search_string, re.IGNORCASE)

answered Aug 15, 2017 at 16:54

Wiktor Stribiżew

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Comments

pkacprzak · Accepted Answer · 2017-08-15 15:59:07Z

1

You can try re.finditer like that:

>>> import re
>>> user_input = "var"
>>> text = "var variable var variable"
>>> regex = r"(?=\b%s\b)" % re.escape(user_input)
>>> [m.start() for m in re.finditer(regex, text)]
[0, 13]

It'll find all matches iteratively.

answered Aug 15, 2017 at 15:59

pkacprzak

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2 Comments

E. Oregel Over a year ago

Where is the output saved to in the loop? Because i would like to break on the first finding and say if it was found, do this, else, do that.

pkacprzak Over a year ago

@E.Oregel then just put this into the loop like this: for m in re.finditer(regex, text): and to inside the loop what you want.

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