Bracket Checking

Question:-

 Write a function matched(s) that takes as input a string s and checks if the brackets "(" and ")" in s are matched: that is, every "(" has a matching ")" after it and every ")" has a matching "(" before it.  Your function should ignore all other symbols that appear in s.  Your function should return True if s has matched brackets and False if it does not.

Here are some examples to show how your function should work.
>>> matched("zb%78")
True
>>> matched("(7)(a")False>>> matched("a)*(?")False>>> matched("((jkl)78(A)&l(8(dd(FJI:),):)?)")True

 Solution:-

def matched(s):
  a = 0
  for i in range(0, len(s)):
    if s[i] == '(':
      if a >= 0:
        a = a + 1
    elif s[i] == ')':
      a = a - 1
  if a == 0:
    return True
  else :
    return False

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