What is the issue here

Question

This is regarding python regex, (Course: Python->Regular Expression->Module 5) (or (|) concept)

In the following example,

import re
pattern = r"gr(a|e)y"
match = re.match(pattern, "gray")
if match:
print ("Match 1") # Output
match = re.match(pattern, "grey")
if match:
print ("Match 2") # Output
match = re.match(pattern, "graey")
if match:
print ("Match 3")

Now when I remove the 'y',

import re
pattern = r"gr(a|e)"
match = re.match(pattern, "gra")
if match:
print("Match 1") # Output
match = re.match(pattern, "gre")
if match:
print("Match 2") # Output
match = re.match(pattern, "grae")
if match:
print("Match 3") # Output

then "Why does the 3rd case match?"

Answer 1

The pattern says
That it should start with "gr" then a or e

grae matches with this condition

It doesn't matter what it has after gra or gre

The same with r"gr(a|e)y" pattern it Only wants gray or grey and doesn't care of anything after that

It will also match greyish and grayish
Hope It Helps You 😊

Answer 2

if you like you can check the match visually with pythex.org:

https://pythex.org/?regex=gr(a%7Ce)&test_string=grae&ignorecase=0&multiline=0&dotall=0&verbose=0

Answer 3

gr(a|e) pattern matches any string starting with "g" ,followed by "r" and then followed by "a" or "e" ,"in grae" it matches "gra"

gr(a|e)y matches string "gr" followed by either one "a" or "e" and then immediately by "y" ,that's why it doesn't gives a match for "greay" since there are two characters("e" and "a") after "gr"

if you want the first pattern to match two characters before "y" you can use gr(a|e)*y now it will match "gr" and then two or more than two "a" or "e" and then check for "y" ,"*" means one or more appearance of a particular character

Answer 4

Thanks Everyone