I have this regular expression r'\b28\b'. In this expression 28 should be dynamic. In other words, 28 is a dynamic value which the user enters. So, instead of 28 it can have 5. In that case, the expression would be r'\b5\b'.
I tried the below two approaches but they are not working.
I want to know how can I do it? Can someone please help me with it?
Contrary to the previous answer, you should generally use r for regular expression strings. But the way you had it, the r was inside the strings. It needs to go outside. It would look like this:
regex = r"\b" + str(my_var) + r"\b"
but in general it's nicer to use raw f-strings. This way you don't have to convert the int to a str yourself:
regex = rf"\b{my_var}\b"
Try running the following to see that it works:
import re
str_to_match = '3 45 72 3 45'
my_var = 45
regex = rf"\b{my_var}\b"
for f in re.findall(regex, str_to_match):
print(f)
Outputs:
45
45
You can use a format string with re.escape, which will escape special characters for you:
import re
room_number = 5
reg_expr = rf"\b{re.escape(str(room_number))}\b"
re.findall(reg_expr, "Room 5 is the target room.")
This outputs:
['5']
[] on Python 3.10 for me.
rf"" instead of f"" because of that \b.rf"\b" from them after my "\b" failed ;-)
Well, if you are like me, I always pre-compile regexes.
(Not sure it always improves performance much, but I just find it a drag to remember both the compiled and the non-compiled syntax, so I picked using only the compiled.)
That solves your problem with f-strings:
import re
data = """
Look for 28
Look for 42
"""
target = 28
patre = re.compile(rf"\b{target}\b")
for line in data.splitlines():
if patre.search(line):
print(line)
Look for 28
re.compile, the re module will automatically compile for us. It encapsulates _compile() function.str(number) initially in that answer, before writing this.