Configuration

Students and instructors often study and teach multiple courses at the same time. You can have multiple configuration files and select one with option -c or --config, e.g.

allowed -c path/to/configuration.json path/to/file.py

If you omit the .json extension, it will be automatically added, i.e. allowed -c my_course file.py and allowed -c my_course.json file.py are equivalent.

The program comes with two configuration files, one for our algorithms and data structures course M269, and one for our introductory Computing course TM112. If no configuration file is given, allowed will use the one for M269.

For example, allowed program.py will check the given program against the constructs taught in M269, while allowed -c tm112 program.py will check it against those taught in TM112.

You can create your own configuration by writing a JSON file of the form

{
   "LANGUAGE": { ... },
   "IMPORTS": { ... },
   "METHODS": { ... }
}

The easiest approach is to download and rename m269.json or tm112.json and edit it to suit your course.

The rest of this document explains the various parts of the JSON file.

LANGUAGE

This entry is a dictionary that maps each unit number to a list of strings describing the syntax and built-in functions introduced in that unit. For example,

"LANGUAGE": {
   "2": ["name", "+", "help"]
}

means that unit 2 introduces names (identifiers), the plus operator and the builtin help function.

For the possible syntactical elements, see dictionary SYNTAX in allowed.py. For the possible built-in functions, see set BUILTINS in the same file.

The various uses of a construct can’t be individually allowed or disallowed. For example, you can’t allow integer addition and disallow string concatenation (or vice versa): you either allow the + operator (and all its uses) or you don’t.

Adding "for" and "while" to "LANGUAGE" only allows the ‘normal’ loops. To also allow the else clause in loops, add "for else" and "while else".

To allow all possible augmented assignments (+=, *=, //=, etc.), add "+=" to "LANGUAGE".

IMPORTS

This entry is a dictionary that maps units to dictionaries of the modules and the list of exported objects introduced in those units. For example,

"IMPORTS": {
   "10": {"math": ["sqrt", "inf"]},
   "11": {"math": ["abs"], "fractions": ["Fraction"]}
}

allows function math.sqrt(x) and constant math.inf from unit 10 onwards, and allows function math.abs(x) and class fractions.Fraction from unit 11 onwards.

METHODS

This entry has the same structure as "IMPORTS", but instead of listing which objects of which modules can be imported, it lists which methods of which classes can be called.

Note that some of the built-in classes are written in lowercase and others in uppercase (see m269.json, the default configuration).

If a unit introduces literals of some type (e.g. lists) in the "LANGUAGE" section, then there should be an entry for the same unit and type in the "METHODS" section. If no methods are allowed, this must be explicitly indicated with an empty list.

In the following example, unit 2 allows any immutable literal (numbers, Booleans, None, strings, tuples), so it must also state which methods are allowed for strings (none in the example) and tuples (only index).

{
   "LANGUAGE": {
      "2": [ "constant", ...],
      ...
   },
   "IMPORTS": { ... },
   "METHODS": {
      "2": {"Tuple": ["index"], "str": []},
      ...
   }
}

⇦ Usage

⇧ Start