I have a class called Pattern, and within it two methods, equates and setwildcard. Equates returns the index in which a substring first appears in a string, and setwildcard sets a wild card character in a substring
p = Pattern('xyz') t = 'xxxxxyz' p.equates(t)
p = Pattern('x*z', '*') t = 'xxxxxgzx' p.equates(t)
Returns 4, because * is the wildcard and can match any letter within t, as long as x and z match. What’s the best way to implement this?
It looks like you’re essentially implementing a subset of regular expressions. Luckily, Python has a library for that built-in! If you’re not familiar with how regular expressions (or, as their friends call them, regexes) work, I highly recommend you read through the documentation for them.
In any event, the function
re.search is, I think, exactly what you’re looking for. It takes, as its first argument, a pattern to match, and, as its second argument, the string to match it in. If the pattern is matched,
search returns an
SRE_Match object, which, conveniently, has a
#start() method that returns the index at which the match starts.
To use the data from your example:
import re start_index = re.search(r'x.z', 'xxxxxgzg').start()
Note that, in regexes,
. – not
* — is the wildcard, so you’ll have to replace them in the pattern you’re using.