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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_code(filename):
 """ This function returns True, if a line of the file contains bracket '{'. """

    with open(filename, "r") as file:
        for line in file:
            # ignore comments and empty lines
            if not is_comment(line) \
                    and '{' in line: # <-- simple indicator for code
                if '${' not in line: # <-- ${abc} variable to substitute
                    return True
    return False