Simple object error

import random

class FileHandler(object):

    def __init__(self, filename = "", query_type = ""):
        self.filename = filename
        self.query_type = query_type

    def line_from_file(self, filename=None, query_type=None):
        if filename != None
            self.filename = filename
        if query_type != None
            self.query_type = query_type
            
        data = [ line.rstrip() for line in open(self.filename) if not line.isspace() ]
        if (self.query_type == "all"):
            return data # Return file as an array
        elif (query_type == "string"):
            return "".join(data) # Return file as a string
        elif (self.query_type == "first"):
            return data[0] # Return first line
        elif (self.query_type == "random" or self.query_type == "rand"):
            return random.choice(data) # Return random line

if __name__ == '__main__':

# I want this to set f.filename to "froge-data.txt" and f.query_type to "first", but they remain empty strings

    f = FileHandler()

    print f.line_from_file("froge_data.txt", "first")