Source code for openepda.expr

# -*- coding: utf-8 -*-

This file contains a parser of analytic expressions.

The parser can be used to parse the analytic expressions and thus
check their correctness in a safe way, and also to evaluate the

The grammar is intended to be very similar to the tinyexpr library
grammar (

Author: Dima Pustakhod
Copyright: 2020, TU/e - PITC and authors
import re
from collections import Counter
from functools import partial
from importlib import import_module
from itertools import chain
from keyword import iskeyword
from keyword import kwlist
from numbers import Real
from operator import contains
from typing import ByteString
from typing import Dict
from typing import List
from typing import MutableSequence
from typing import Sequence
from typing import Union

import tatsu
from more_itertools import collapse
from tatsu.exceptions import FailedParse

# grammar symbols
OPERATORS = tuple("+-*/^%")
BRACKETS = tuple("()")
LIST_SEPARATOR = tuple(",")
LETTERS_LOWER = tuple("abcdefghijklmnopqrstuvwxyz")
LETTERS_UPPER = tuple(l.upper() for l in LETTERS_LOWER)
DIGITS = tuple("0123465789")
UNDERSCORE = tuple("_")
SPACE = tuple(" ")

    + DIGITS
    + SPACE

# template includes placeholders for optional items. In the comments are
# examples of what should be in the placeholder.
    @@grammar :: openepda_expr
    @@whitespace :: / +/

    start = list $ ;
    list = expr ',' list | expr ;
    expr = expr {{('+' | '-') term}} | term ;
    term = term '%' factor | term '*' factor | term '/' factor | factor ;
    factor = factor "{power_op}" power | power ;  # association right or left
    power = '+' power | '-' power | base ;
    base = number 
           {func2_base}  # | func2 '(' expr ',' expr ')'       
           {func1_base}  # | func1 '(' expr ')'
           {allow_skip_parenth}  # | func1 power  # optional 
           {allow_parenth_after_const}  # | const '(' ')'  # optional 
           {const_base}  # | const  # optional 
           | var
           | "(" list ")" ;
    number = /\d*\.\d+[eE][+-]?\d+/ 
             | /\d+\.?[eE][+-]?\d+/ 
             | /\d*\.\d+/ 
             | /\d+\.?/ ;           
    {const_list}  # const = 'e' | 'pi' ; 
    {func1_list}  # func1 = 'abs' | 'acos' | 'asin' | 'atan' | 'ceil' | 'cos' 
                  # | 'cosh' |'exp' | 'fac' | 'floor' | 'ln' | 'log' | 'log10'  
                  # | 'sin' |'sinh' | 'sqrt' | 'tan' | 'tanh' ;
    {func2_list}  # func2 = 'atan2' | 'pow' | 'npr' | 'ncr' ;
    # var = /[a-zA-Z][a-zA-Z0-9_]*/ ;
    var = {exclude} var:/[a-zA-Z][a-zA-Z0-9_]*/;

CHOICES_TEMPLATE = "{name} = {choices_str} ;"
EXCLUDE_TEMPLATE = "! ( {choices_str} )"

# Predefined identifiers
CONSTANTS_MAP = {"pi": ("math", "pi"), "e": ("math", "e")}

# Mapping of functions available in the expressions, 1 and 2 parameters
    "abs": ("math", "fabs"),
    "acos": ("math", "acos"),
    "asin": ("math", "asin"),
    "atan": ("math", "atan"),
    "ceil": ("math", "ceil"),
    "cos": ("math", "cos"),
    "cosh": ("math", "cosh"),
    "exp": ("math", "exp"),
    "fac": ("math", "factorial"),
    "floor": ("math", "floor"),
    "ln": ("math", "log"),
    "log": ("math", "log"),  # option to use log10
    "log10": ("math", "log10"),
    "sin": ("math", "sin"),
    "sinh": ("math", "sinh"),
    "sqrt": ("math", "sqrt"),
    "tan": ("math", "tan"),
    "tanh": ("math", "tanh"),

    "atan2": ("math", "atan2"),
    "pow": ("math", "pow"),
    "ncr": ("scipy.special", "comb"),
    "npr": ("scipy.special", "perm"),

# Aliases under which the functions can be imported from math
    "abs": "fabs",
    "fac": "factorial",
    "ln": "log",
    "log": "log10",

[docs]class OpenEpdaError(Exception): pass
[docs]class OpenEpdaExpressionError(Exception): pass
class _BaseParser(object): def __init__( self, allow_skip_parenth=False, use_nat_log=True, power_from_right=True, use_caret_for_power=True, constants=None, functions_1=None, functions_2=None, allow_parenth_after_const=False, parameters=(), exclude=(), ): """Create a parser. `constants`, `functions_1`, `functions_2` are dictionaries in the form: {'expression_name': ('module_name', 'module_attribute')}. `parameters` are just an iterable with variable identifiers. Their values are submitted to the eval method. Parameters ---------- allow_skip_parenth : bool if True, in expressions with function of one argument (e.g. 'sin 0.5') parentheses can be omitted. If False, parentheses are required. Note, that if this option is True, parsing of the expression is possible, but evaluation is not currently supported. use_nat_log : bool if True, `log` evaluates to the natural logarithm. Otherwise, it is log10. power_from_right : bool if True, the following association rules are used for exponentiation: `a^b^c == a^(b^c)` and `-a^b == -(a^b)`. This is default Python behavior. If False, the following rules are used: `a^b^c == (a^b)^c` and `-a^b == (-a)^b`. Note, that if this option is True, parsing of the expression is possible, but evaluation is not currently supported. use_caret_for_power : bool if True, caret symbol '^' will be used for power operation. Otherwise, a standard python operator '**' is used. constants : dict constants to be allowed in the expression. functions_1 : dict list of functions of 1 argument to be allowed in the expression. functions_2 : dict list of functions of 2 arguments to be allowed in the expression. parameters : list list of parameter identifiers to be allowed in the expression. exclude : iterable of str identifiers to be excluded from the final list """ # parsing options self._allow_parenth_after_const = allow_parenth_after_const self._use_caret_for_power = use_caret_for_power self._allow_skip_parenth = allow_skip_parenth # not used self._power_from_right = power_from_right # not used # evaluation option self._use_nat_log = use_nat_log self._exclude = exclude constants = constants or {} functions_1 = functions_1 or {} functions_2 = functions_2 or {} # member variables self._parser = None self._imported_symbols = {} # import and add symbols self._check_symbols(constants.keys()) added_symbols = self._add_symbols(constants, exclude=self._exclude) self._constants = added_symbols self._check_symbols(functions_1.keys()) added_symbols = self._add_symbols(functions_1, exclude=self._exclude) self._f1 = added_symbols self._check_symbols(functions_2.keys()) added_symbols = self._add_symbols(functions_2, exclude=self._exclude) self._f2 = added_symbols self._check_symbols(parameters) self._vars = parameters # create parser self.compile_parser() def _check_symbols(self, symbols): """Check if the symbols are allowed in the expression The check will not pass if: - there are repetitions inside symbols - any symbol was already defined before in this parser - any symbol is the same as a python keyword Parameters ---------- symbols : iterable of str Returns ------- True Raises ------ ValueError: if the check fails. """ if len(symbols) == 0: return True # check there is no repeated symbols repeated_symb, no_repetitions = Counter(symbols).most_common()[0] if no_repetitions > 1: raise OpenEpdaExpressionError( 'Symbol "{}" is defined more than once ({} times).'.format( repeated_symb, no_repetitions ) ) # Check each symbol for s in symbols: if iskeyword(s): # python keywords raise OpenEpdaExpressionError( 'Symbol "{}" is a reserved keyword in python.'.format(s) ) elif s in self._imported_symbols.keys(): # already defined symbols raise OpenEpdaExpressionError( 'Symbol "{}" is already defined.'.format(s) ) return True @property def reserved_identifiers(self): return tuple(self._imported_symbols) def _add_symbols(self, symbols, exclude=()): """ Parameters ---------- symbols : dict exclude : iterable of str Returns ------- tuple of str list of imported symbols """ res = make_symbol_mapping(symbols, exclude=exclude) self._imported_symbols.update(res) return tuple(res.keys()) def compile_parser(self): """Create a parser. This is an expensive action, so preferably has to be done only once. Parsing itself is much faster. """ # Create data to fill grammar template # lists of symbols const_list = make_grammar_choice_item("const", self._constants) func1_list = make_grammar_choice_item("func1", self._f1) func2_list = make_grammar_choice_item("func2", self._f2) const_base = r"| const" if const_list else "" func1_base = r"| func1 '(' expr ')'" if func1_list else "" func2_base = r"| func2 '(' expr ',' expr ')'" if func2_list else "" exclude = make_grammar_exclude_item( kwlist, self._constants, self._f1, self._f2 ) # optional items if self._allow_skip_parenth and func1_list: allow_skip_parenth = "| func1 power" else: allow_skip_parenth = "" if self._allow_parenth_after_const and const_list: allow_parenth_after_const = "| const '(' ')'" else: allow_parenth_after_const = "" power_op = "^" if self._use_caret_for_power else "**" grammar = GRAMMAR_TEMPLATE.format( power_op=power_op, const_base=const_base, const_list=const_list, func1_base=func1_base, func1_list=func1_list, func2_base=func2_base, func2_list=func2_list, allow_skip_parenth=allow_skip_parenth, allow_parenth_after_const=allow_parenth_after_const, exclude=exclude, ) # print(grammar) self._parser = tatsu.compile(grammar) def parse(self, expr): """Parse the expression. Parameters ---------- expr : str expression to be parsed Returns ------- tatsu.contexts.closure AST for the expression """ if not self._parser: raise OpenEpdaExpressionError("Parser has not been created yet.") if expr == "": raise OpenEpdaExpressionError("Cannot parse empty expression") try: ast = self._parser.parse(expr) except FailedParse as e: raise OpenEpdaExpressionError( "error parsing expression '{}': {}.".format(expr, e) ) return ast def get_parameter_names(self, expr): """Parse expression and get the names of parameters used in it. Parameters ---------- expr : str expression to the parsed Returns ------- list of str list of parameter names present in the expression """ ast = self.parse(expr) flat_ast = collapse(ast, base_type=dict) param_names = [ item["var"] for item in flat_ast if isinstance(item, dict) ] return param_names def eval(self, expr, params=None): """ Parameters ---------- expr : str expression to be evaluated params : Dict[str, Any] {'parameter_name': parameter_value} Returns ------- Any evaluation result """ if not self._power_from_right: raise NotImplementedError( "Evaluations of expressions with left association of " "exponentiation is not implemented." ) if self._allow_skip_parenth: raise NotImplementedError( "Evaluations of expressions with missing parentheses " "for a function of one argument is not implemented." ) params = params or {} self.check_missing_params(expr, params.keys()) if self._allow_parenth_after_const: for c in self._constants: expr = re.sub(r"{}\( *\)".format(c), "{}".format(c), expr) if self._use_caret_for_power: expr = expr.replace("^", "**") res = eval(expr, self._imported_symbols, params) return res def check_missing_params(self, expr, params): """Verify that all params that are present in the expr are present. Parameters ---------- expr : str params : iterable of str allowed parameters """ actual_param_names = self.get_parameter_names(expr) missing_params = set(actual_param_names) - set(params) if missing_params: raise OpenEpdaExpressionError( "expression '{}' contains undefined params: {}.".format( expr, missing_params ) ) else: return True
[docs]def make_choice_list(*choices, exclude=()): """Combine choices into a single list with unique items. Some of the choices can be excluded. Parameters ---------- choices : iterable of str each iterable contains a list of functions to be included into the symbols. exclude: iterable of str list of symbols to be excluded. Returns ------- list of str sorted list of symbols, where all choices are united, and strings from exclude parameter are removed. """ choices_clean = sorted(set(chain.from_iterable(choices))) ch = list(c for c in choices_clean if c not in exclude) return ch
[docs]def make_symbol_mapping(mapping, exclude=()): """Import all symbols from the mapping using their name Parameters ---------- mapping : Dict[str, Tuple(str, str)] keys are symbol names, values are 2-tuples. value[0] is a module name, value[1] is attribute name to be imported from this module and to be used under symbol name. exclude : iterable of str identifiers to be excluded from the final list Returns ------- Dict[str, Any] keys are imported symbol names, values are imported entities, e.g. function, parameters, etc. """ res = {} for symbol_name, (module_name, attr) in mapping.items(): if symbol_name in exclude: continue m = import_module(module_name) try: symbol = getattr(m, attr) except AttributeError as e: raise ValueError( "Incorrect data for symbol '{}', cannot import it: {}.".format( symbol_name, e ) ) res.update({symbol_name: symbol}) return res
[docs]def make_choice_str(choices=None): """ Parameters ---------- choices : iterable of str Returns ------- str """ if choices: choices_str = "' | '".join(choices) if choices_str != "": choices_str = "'{}'".format(choices_str) else: choices_str = "" return choices_str
def make_grammar_choice_item(name="", choices=None): choices_str = make_choice_str(choices) if choices_str != "": res = CHOICES_TEMPLATE.format(name=name, choices_str=choices_str) else: res = "" return res def make_grammar_exclude_item(*choices): choices_flat = chain.from_iterable(choices) choices_str = make_choice_str(choices_flat) if choices_str != "": res = EXCLUDE_TEMPLATE.format(choices_str=choices_str) else: res = "" return res
[docs]def check_parameter_name(name, reserved=()): """Check if name can be used as identifier in the expression. - Contains letters, underscores, or digits - Starts with a letter - Is not a python keyword - Is not one of the reserved identifiers Parameters ---------- name : str identifier to be checked reserved : iterable of str identifiers which are reserved and are therefore illegal, e.g. for other functions. Returns ------- bool True if name is a correct identifier """ if not (name[0] in LETTERS_LOWER or name[0] in LETTERS_UPPER): # First symbol raise OpenEpdaExpressionError( 'First symbol of the parameter name "{}" is not one of allowed' " symbols.".format(name) ) elif set(name) - set(VARIABLE_NAME): # Other symbols raise OpenEpdaExpressionError( 'Parameter name "{}" contains symbol(s) which is (are) not ' "letters or an underscore.".format(name) ) elif iskeyword(name): # python keywords raise OpenEpdaExpressionError( 'Parameter name "{}" is a reserved keyword in python.'.format(name) ) elif name in reserved: raise OpenEpdaExpressionError( 'Parameter name "{}" is a reserved identifier.'.format(name) ) else: return True
def check_expr(expr): if not isinstance(expr, str): raise TypeError( "Expression is not a str type. It is {}.".format(type(expr)) ) expr = expr.replace(" ", "") # remove whitespaces if any(map(partial(contains, expr), kwlist)): raise OpenEpdaExpressionError( "Expression contains a reserved python keyword." ) elif not all(map(partial(contains, ALLOWED_SYMBOLS), expr)): raise OpenEpdaExpressionError("Expression contains illegal symbols.") else: return True openepda_parser = _BaseParser( functions_1=STANDARD_FCNS_1_ARG_MAP, functions_2=STANDARD_FCNS_2_ARG_MAP, constants=CONSTANTS_MAP, exclude="ln", ) TNestedSequence = Union[str, Real, Sequence["TNestedSequence"]] TNestedRealSequence = Union[Real, Sequence["TNestedRealSequence"]] TNestedRealList = Union[Real, List["TNestedRealList"]]
[docs]def evaluate_expression( expr: TNestedSequence, params=None ) -> Union[Real, TNestedRealList]: """Evaluate expression if necessary and return a numeric value. Parameters ---------- expr : TNestedSequence expression to be checked and evaluated if needed. Can be a sequence of expressions, or a sequence of sequences... params : Optional[Dict[str, Any]] Parameter values to be used during expression evaluation. We do not restrict parameter values to the Real type, however, this could make sense. It depends on whether the functions used in the expression are able to produce numeric output for non-numeric inputs. Returns ------- res : Union[Real, TNestedRealList] the input expression if it is a number, or the expression evaluation result if it is a number. Raises ------ TypeError In cases when the expression cannot be evaluated, or when it returned a non-numeric result. """ if isinstance(expr, Real): res = expr elif isinstance(expr, str): res = openepda_parser.eval(expr, params=params) if not isinstance(res, Real): raise TypeError( "Expression '{}' was evaluated, and a non-numeric type {} " "was returned. Evaluation result: {}.".format( expr, type(res), res ) ) elif isinstance(expr, (MutableSequence, list)): res = [evaluate_expression(e, params=params) for e in expr] elif isinstance(expr, tuple): res = tuple(evaluate_expression(e, params=params) for e in expr) elif isinstance(expr, Sequence) and not isinstance(ByteString): res = tuple(evaluate_expression(e, params=params) for e in expr) else: raise TypeError( "Provided input '{}' has type {}. It is not a string or a number, " "and therefore cannot be evaluated as a numeric value. ".format( expr, type(expr) ) ) return res