Since we use special characters in regular expressions to match the beginning or end of a line or specify wild cards, we need a way to indicate that these characters are “normal” and we want to match the actual character such as a dollar-sign or caret.
We can indicate that we want to simply match a character by prefixing that character with a backslash. For example, we can find money amounts with the following regular expression.
import re x = 'We just received $10.00 for cookies.' y = re.findall('\$[0-9.]+',x)
Since we prefix the dollar-sign with a backslash, it actually matches the dollar-sign in the input string instead of matching the “end of line” and the rest of the regular expression matches one or more digits or the period character. Note: In between square brackets, characters are not “special”. So when we say “[0-9.]”, it really means digits or a period. Outside of square brackets, a period is the “wild-card” character and matches any character. In between square brackets, the period is a period.