Find substring in string but only if whole words?

Question

What is an elegant way to look for a string within another string in Python, but only if the substring is within whole words, not part of a word?

Perhaps an example will demonstrate what I mean:

string1 = "ADDLESHAW GODDARD" string2 = "ADDLESHAW GODDARD LLP" assert string_found(string1, string2)  # this is True string1 = "ADVANCE" string2 = "ADVANCED BUSINESS EQUIPMENT LTD" assert not string_found(string1, string2)  # this should be False 

How can I best write a function called string_found that will do what I need? I thought perhaps I could fudge it with something like this:

def string_found(string1, string2):    if string2.find(string1 + " "):       return True    return False 

But that doesn't feel very elegant, and also wouldn't match string1 if it was at the end of string2. Maybe I need a regex? (argh regex fear)

Answer 1

You can use regular expressions and the word boundary special character \b (highlight by me):

Matches the empty string, but only at the beginning or end of a word. A word is defined as a sequence of alphanumeric or underscore characters, so the end of a word is indicated by whitespace or a non-alphanumeric, non-underscore character. Note that \b is defined as the boundary between \w and \W, so the precise set of characters deemed to be alphanumeric depends on the values of the UNICODE and LOCALE flags. Inside a character range, \b represents the backspace character, for compatibility with Python’s string literals.

def string_found(string1, string2):    if re.search(r"\b" + re.escape(string1) + r"\b", string2):       return True    return False 

Demo

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If word boundaries are only whitespaces for you, you could also get away with pre- and appending whitespaces to your strings:

def string_found(string1, string2):    string1 = " " + string1.strip() + " "    string2 = " " + string2.strip() + " "    return string2.find(string1)