simplepy

An interpreter for a subset of the Python language, written purely in Dart. It is intended for adding scripting capabilities to Dart projects and for educational purposes.

Features

  • Available python features:

    • Variable types: int, float, bool, str, list, dict, set, tuple, NoneType
      (some dict methods with limitations)
    • r-strings, f-strings: {value:[[fill]align][sign][0][width][.precision][dfs]} ; #, and types b/o/x/e/g/% are not yet supported.
    • arithmetic operators: + - * / // ** % and bitwise operators
    • assignments: = += -= *= /= **= //= %=
    • comparisons: == > >= < <= !=
    • boolean operators: and, or, not
    • if, else, elif
    • for loops, while loops (but else: block is not yet available)
    • try/except/else/finally
    • functions (default arguments, *args, **kwargs are partially implemented), lambda functions
    • some built-in functions: print(), range(), len(), str(), repr(), int(), float(), bool(), type(), list(), dict(), set(), tuple(), abs(), round(), min(), max(), hex(), oct(), bin(), pow(), sum(), ord(), chr(), isinstance()
    • list, dict and set comprehensions
    • list, string and tuple slices - read only
    • classes (no class attributes, no multiple inheritance)
    • global and nonlocal variables
    • limited file I/O: files can be created using f=open(filename,mode). mode can be w,r,a,w+,r+,a+. No binary files. Available methods: f.read(n), f.readline(n), f.readlines(n), f.write(text), f.writelines(list), f.seek(position), f.close() File contents are kept in memory in a dictionary as long as the Interpreter object exists. To make them persistent, you can access them from dart by interpreter.vfs[filename].
    • import (only modules from virtual file system or standard modules, no packages yet). Available standard modules:
      • json (functions: dump, dumps, load, loads)
      • math (constants: e, nan, inf, pi, tau; functions: exp, log, log2, log10, pow, sqrt, cbrt, sin, cos, tan, asin, acos, atan, atan2, degrees, radians)
      • random (functions: choice, gauss, randint, random, randrange, seed, uniform)
      • re (functions: findall, match, search, split, sub. Optional parameters flags, count, maxsplit are not supported yet)
      • time (functions: sleep (blocking the execution), time, time_ns)

    Some more features might be added soon, but this will never become a full python interpreter.

  • Missing python features:

    • dict.key(), dict.values(), dict.items() return list copies, not dynamic views as in Python
    • set operators | & - ^ <= >= (but available as set1.union(set2)` etc.)
    • ternary conditional expressions
    • :=operator
    • slice assignments (like x[5:10] = [1,2,3]))
    • decorators
    • async functions, generators
    • input() and some other built-in functions
    • complex numbers
    • multiple statements in one line separated by ;
    • dunder methods (__xxx__) except for __init__
    • anything else not mentioned as available

Usage

import 'package:simplepy/simplepy.dart';

void main() {
  String py = """
print(3**4)
6.0*7
""";
  final tokens = Lexer(py).scanTokens();
  final stmts = Parser(tokens).parse();
  var result = Interpreter().interpret(stmts);
  print("result = $result (${result.runtimeType})");
}

Additional information

Please report any errors (except for missing features, that are not mentioned as available) at the issue tracker.

Libraries

simplepy
simplepy_io