Python Regular Expression Character following match does not equal

Question

I am trying to match a string if it starts with '123' but only if the immediate following character is not a numeric.

For example, these would match:

• '123'
• '123.4'
• '123A'

But these would not match:

• '124'
• '1234'
• '1235.3'

If I was only concerned with the string not ending with a numeric I could use:

'^123(?!.*\d$)'

However, this is NOT what I am looking for. I am looking for whether the character immediately following my match string is not a numeric.

Answer 1

anubhava's answer is correct, you can also use this which I think is simpler :

^123\D{1}

\D matches any non-digit character. you can replace {1} with any quantifier of your choice

Maybe you want to capture the full string, in that case you can modify :

^123\D{1}.*

Demo

Answer 2

I am looking for whether the character immediately following my match string is not a numeric.

You can use this regex:

^123(?!\d)

(?!\d) is negative lookahead that will assert failure if next character after 123 is a digit.

RegEx Demo