Python SyntaxError: invalid syntax in if statement line

I cannot run my python script because there is an snytax error in the line of "if contained" and i don't know why. Can someon please help me.

for aType in attributeTypes:
    contained = True
    for argument in arguments:
        if argument == aType:
            contained = False
            break
    if contained
        output_data_string += "@attribute " + argument + " " + attributeTypes[aType] + "\n"