def check_dependencies():
available = []<EOL>try:<EOL><INDENT>shell('<STR_LIT>')<EOL>available.append('<STR_LIT>')<EOL><DEDENT>except OSError:<EOL><INDENT>pass<EOL><DEDENT>try:<EOL><INDENT>shell('<STR_LIT>')<EOL>available.append('<STR_LIT>')<EOL><DEDENT>except OSError:<EOL><INDENT>pass<EOL><DEDENT>if not available:<EOL><INDENT>sys.exit(error('<STR_LIT>'))<EOL><DEDENT>check_dependency_epubcheck()<EOL>return available<EOL>
Check external dependecies
    Return a tuple with the available generators.