Source code for sympy.printing.jscode

Javascript code printer

The JavascriptCodePrinter converts single sympy expressions into single
Javascript expressions, using the functions defined in the Javascript
Math object where possible.


from __future__ import print_function, division

from sympy.core import S
from sympy.codegen.ast import Assignment
from sympy.printing.codeprinter import CodePrinter
from sympy.printing.precedence import precedence, PRECEDENCE
from sympy.core.compatibility import string_types, range

# dictionary mapping sympy function to (argument_conditions, Javascript_function).
# Used in JavascriptCodePrinter._print_Function(self)
known_functions = {
    'Abs': 'Math.abs',
    'sin': 'Math.sin',
    'cos': 'Math.cos',
    'tan': 'Math.tan',
    'acos': 'Math.acos',
    'asin': 'Math.asin',
    'atan': 'Math.atan',
    'atan2': 'Math.atan2',
    'ceiling': 'Math.ceil',
    'floor': 'Math.floor',
    'sign': 'Math.sign',
    'exp': 'Math.exp',
    'log': 'Math.log',

[docs]class JavascriptCodePrinter(CodePrinter): """"A Printer to convert python expressions to strings of javascript code """ printmethod = '_javascript' language = 'Javascript' _default_settings = { 'order': None, 'full_prec': 'auto', 'precision': 17, 'user_functions': {}, 'human': True, 'contract': True } def __init__(self, settings={}): CodePrinter.__init__(self, settings) self.known_functions = dict(known_functions) userfuncs = settings.get('user_functions', {}) self.known_functions.update(userfuncs) def _rate_index_position(self, p): return p*5 def _get_statement(self, codestring): return "%s;" % codestring def _get_comment(self, text): return "// {0}".format(text) def _declare_number_const(self, name, value): return "var {0} = {1};".format(name, value.evalf(self._settings['precision'])) def _format_code(self, lines): return self.indent_code(lines) def _traverse_matrix_indices(self, mat): rows, cols = mat.shape return ((i, j) for i in range(rows) for j in range(cols)) def _get_loop_opening_ending(self, indices): open_lines = [] close_lines = [] loopstart = "for (var %(varble)s=%(start)s; %(varble)s<%(end)s; %(varble)s++){" for i in indices: # Javascript arrays start at 0 and end at dimension-1 open_lines.append(loopstart % { 'varble': self._print(i.label), 'start': self._print(i.lower), 'end': self._print(i.upper + 1)}) close_lines.append("}") return open_lines, close_lines def _print_Pow(self, expr): PREC = precedence(expr) if expr.exp == -1: return '1/%s' % (self.parenthesize(expr.base, PREC)) elif expr.exp == 0.5: return 'Math.sqrt(%s)' % self._print(expr.base) else: return 'Math.pow(%s, %s)' % (self._print(expr.base), self._print(expr.exp)) def _print_Rational(self, expr): p, q = int(expr.p), int(expr.q) return '%d/%d' % (p, q) def _print_Indexed(self, expr): # calculate index for 1d array dims = expr.shape elem = S.Zero offset = S.One for i in reversed(range(expr.rank)): elem += expr.indices[i]*offset offset *= dims[i] return "%s[%s]" % (self._print(expr.base.label), self._print(elem)) def _print_Idx(self, expr): return self._print(expr.label) def _print_Exp1(self, expr): return "Math.E" def _print_Pi(self, expr): return 'Math.PI' def _print_Infinity(self, expr): return 'Number.POSITIVE_INFINITY' def _print_NegativeInfinity(self, expr): return 'Number.NEGATIVE_INFINITY' def _print_Piecewise(self, expr): if expr.args[-1].cond != True: # We need the last conditional to be a True, otherwise the resulting # function may not return a result. raise ValueError("All Piecewise expressions must contain an " "(expr, True) statement to be used as a default " "condition. Without one, the generated " "expression may not evaluate to anything under " "some condition.") lines = [] if expr.has(Assignment): for i, (e, c) in enumerate(expr.args): if i == 0: lines.append("if (%s) {" % self._print(c)) elif i == len(expr.args) - 1 and c == True: lines.append("else {") else: lines.append("else if (%s) {" % self._print(c)) code0 = self._print(e) lines.append(code0) lines.append("}") return "\n".join(lines) else: # The piecewise was used in an expression, need to do inline # operators. This has the downside that inline operators will # not work for statements that span multiple lines (Matrix or # Indexed expressions). ecpairs = ["((%s) ? (\n%s\n)\n" % (self._print(c), self._print(e)) for e, c in expr.args[:-1]] last_line = ": (\n%s\n)" % self._print(expr.args[-1].expr) return ": ".join(ecpairs) + last_line + " ".join([")"*len(ecpairs)]) def _print_MatrixElement(self, expr): return "{0}[{1}]".format(self.parenthesize(expr.parent, PRECEDENCE["Atom"], strict=True), expr.j + expr.i*expr.parent.shape[1])
[docs] def indent_code(self, code): """Accepts a string of code or a list of code lines""" if isinstance(code, string_types): code_lines = self.indent_code(code.splitlines(True)) return ''.join(code_lines) tab = " " inc_token = ('{', '(', '{\n', '(\n') dec_token = ('}', ')') code = [ line.lstrip(' \t') for line in code ] increase = [ int(any(map(line.endswith, inc_token))) for line in code ] decrease = [ int(any(map(line.startswith, dec_token))) for line in code ] pretty = [] level = 0 for n, line in enumerate(code): if line == '' or line == '\n': pretty.append(line) continue level -= decrease[n] pretty.append("%s%s" % (tab*level, line)) level += increase[n] return pretty
[docs]def jscode(expr, assign_to=None, **settings): """Converts an expr to a string of javascript code Parameters ========== expr : Expr A sympy expression to be converted. assign_to : optional When given, the argument is used as the name of the variable to which the expression is assigned. Can be a string, ``Symbol``, ``MatrixSymbol``, or ``Indexed`` type. This is helpful in case of line-wrapping, or for expressions that generate multi-line statements. precision : integer, optional The precision for numbers such as pi [default=15]. user_functions : dict, optional A dictionary where keys are ``FunctionClass`` instances and values are their string representations. Alternatively, the dictionary value can be a list of tuples i.e. [(argument_test, js_function_string)]. See below for examples. human : bool, optional If True, the result is a single string that may contain some constant declarations for the number symbols. If False, the same information is returned in a tuple of (symbols_to_declare, not_supported_functions, code_text). [default=True]. contract: bool, optional If True, ``Indexed`` instances are assumed to obey tensor contraction rules and the corresponding nested loops over indices are generated. Setting contract=False will not generate loops, instead the user is responsible to provide values for the indices in the code. [default=True]. Examples ======== >>> from sympy import jscode, symbols, Rational, sin, ceiling, Abs >>> x, tau = symbols("x, tau") >>> jscode((2*tau)**Rational(7, 2)) '8*Math.sqrt(2)*Math.pow(tau, 7/2)' >>> jscode(sin(x), assign_to="s") 's = Math.sin(x);' Custom printing can be defined for certain types by passing a dictionary of "type" : "function" to the ``user_functions`` kwarg. Alternatively, the dictionary value can be a list of tuples i.e. [(argument_test, js_function_string)]. >>> custom_functions = { ... "ceiling": "CEIL", ... "Abs": [(lambda x: not x.is_integer, "fabs"), ... (lambda x: x.is_integer, "ABS")] ... } >>> jscode(Abs(x) + ceiling(x), user_functions=custom_functions) 'fabs(x) + CEIL(x)' ``Piecewise`` expressions are converted into conditionals. If an ``assign_to`` variable is provided an if statement is created, otherwise the ternary operator is used. Note that if the ``Piecewise`` lacks a default term, represented by ``(expr, True)`` then an error will be thrown. This is to prevent generating an expression that may not evaluate to anything. >>> from sympy import Piecewise >>> expr = Piecewise((x + 1, x > 0), (x, True)) >>> print(jscode(expr, tau)) if (x > 0) { tau = x + 1; } else { tau = x; } Support for loops is provided through ``Indexed`` types. With ``contract=True`` these expressions will be turned into loops, whereas ``contract=False`` will just print the assignment expression that should be looped over: >>> from sympy import Eq, IndexedBase, Idx >>> len_y = 5 >>> y = IndexedBase('y', shape=(len_y,)) >>> t = IndexedBase('t', shape=(len_y,)) >>> Dy = IndexedBase('Dy', shape=(len_y-1,)) >>> i = Idx('i', len_y-1) >>> e=Eq(Dy[i], (y[i+1]-y[i])/(t[i+1]-t[i])) >>> jscode(e.rhs, assign_to=e.lhs, contract=False) 'Dy[i] = (y[i + 1] - y[i])/(t[i + 1] - t[i]);' Matrices are also supported, but a ``MatrixSymbol`` of the same dimensions must be provided to ``assign_to``. Note that any expression that can be generated normally can also exist inside a Matrix: >>> from sympy import Matrix, MatrixSymbol >>> mat = Matrix([x**2, Piecewise((x + 1, x > 0), (x, True)), sin(x)]) >>> A = MatrixSymbol('A', 3, 1) >>> print(jscode(mat, A)) A[0] = Math.pow(x, 2); if (x > 0) { A[1] = x + 1; } else { A[1] = x; } A[2] = Math.sin(x); """ return JavascriptCodePrinter(settings).doprint(expr, assign_to)
def print_jscode(expr, **settings): """Prints the Javascript representation of the given expression. See jscode for the meaning of the optional arguments. """ print(jscode(expr, **settings))