While trying to learn a little more about regular expressions, a tutorial suggested that you can use the \b to match a word boundary. However, the following snippet in the Python interpreter does not work as expected:
>>> x = 'one two three'
>>> y = re.search("\btwo\b", x)
It should have been a match object if anything was matched, but it is None.
Is the \b expression not supported in Python or am I using it wrong?
Just to explicitly explain why re.search("\btwo\b", x) doesn't work, it's because \b in a Python string is shorthand for a backspace character.
print("foo\bbar")
fobar
So the pattern "\btwo\b" is looking for a backspace, followed by two, followed by another backspace, which the string you're searching in (x = 'one two three') doesn't have.
To allow re.search (or compile) to interpret the sequence \b as a word boundary, either escape the backslashes ("\\btwo\\b") or use a raw string to create your pattern (r"\btwo\b").
just a note, for dynamic variable this will not work
x = 'one two three'
dy = "two"
y = re.search(r"\b" + dy + "\b", x)
print(y) # None
use r"\b" on left and right
x = 'one two three'
dy = "two"
y = re.search(r"\b" + dy + r"\b", x)
print(y) # <re.Match object; span=(4, 7), match='two'>