I'm following a tutorial about regular expression. I'm getting an error when doing the following:
regex = r'(+|-)?\d*\.?\d*'
Apparently, Python doesn't like (+|-). What could be the problem?
Also, what could be the issue with not adding r ahead of the regex?
You need to escape + in regular expressions to get a literal +, because it usually means "one or more instances of something":
regex = r'(\+|-)?\d*\.?\d*'
And r makes it a "raw" string. Without the r, the regular expression escape sequences will be interpreted as string escape sequences, and they'll cause all sorts of problems. (\b being a backspace instead of a word boundary, and that kind of thing.)
+ is a special character. You can use brackets to specify a range of characters, which is better than using an "or" with the pipe character in this case.:
regex = r'([+-])?\d*\.?\d*'
Otherwise, you just need to escape it in your original version:
regex = r'(\+|-)?\d*\.?\d*'
Using the r is the preferred way of specifying a regex string in python because it indicates a raw string, which should not be interpreted and reduces the amount of escaping you must perform with backslashes. It is just a python regex idiom you will see everywhere.
r'(\+|-)?\d*\.?\d*'
#'(\\+|-)?\\d*\\.?\\d*'
