Regex string matched failure -

i not understand how regex string matching works

r2 = r'a[bcd]*b' m1 = re.findall(r2,"abcbd") abcb 

this falls in line explained in regex

step 3 engine tries match b, current position @ end of string, fails.

how?i not understand this?

your regular expression requires match end in b, therefore matched trailing d. if b optional, in a[bcd]*b?, entire string matched.