pyValidateBrackets

# A function to validate a character string containing nested matching pairs of brackets

def myvalid(mystr):
    openlist = "({[<"                   # List of possible opening brackets
    closlist = ")}]>"                   # List of corresponding closing brackets
    closexpect = ["-"] * len(mystr)     # Will be used to hold the valid close bracket per level
    level = 0                           # Initialise a level counter
    for c in mystr:                     # Examine input string characters one by one
        if c in openlist:               # Have we found an opening bracket?
            level += 1                  # - yes - go up one level
            idx = openlist.find(c)      # get the index position of the opening bracket
            closexpect[level] = closlist[idx]       # store the expected closing bracket for this level
        elif c == closexpect[level]:    # Have we found the expected closing bracket for this level?
            level -= 1                  # - yes - go down one level
        elif c in closlist:             # Have we found an unexpected closing bracket?
            return False                # - yes - exit with error
    # We have reached the end of the input string. We should be back at level zero
    return not level                    # level zero returns True, any other level returns False

print(myvalid('({})({})'))
print(myvalid('({})([})'))
print(myvalid('{({})[{}]}'))

# Results: True, False, True