"""
pint.pint_eval
~~~~~~~~~~~~~~
An expression evaluator to be used as a safe replacement for builtin eval.
:copyright: 2016 by Pint Authors, see AUTHORS for more details.
:license: BSD, see LICENSE for more details.
"""
import operator
import token as tokenlib
from .errors import DefinitionSyntaxError
# For controlling order of operations
_OP_PRIORITY = {
"**": 3,
"^": 3,
"unary": 2,
"*": 1,
"": 1, # operator for implicit ops
"//": 1,
"/": 1,
"%": 1,
"+": 0,
"-": 0,
}
def _power(left, right):
from .compat import is_duck_array
from .quantity import Quantity
if (
isinstance(left, Quantity)
and is_duck_array(left.magnitude)
and left.dtype.kind not in "cf"
and right < 0
):
left = left.astype(float)
return operator.pow(left, right)
_BINARY_OPERATOR_MAP = {
"**": _power,
"*": operator.mul,
"": operator.mul, # operator for implicit ops
"/": operator.truediv,
"+": operator.add,
"-": operator.sub,
"%": operator.mod,
"//": operator.floordiv,
}
_UNARY_OPERATOR_MAP = {"+": lambda x: x, "-": lambda x: x * -1}
[docs]class EvalTreeNode:
"""Single node within an evaluation tree
left + operator + right --> binary op
left + operator --> unary op
left + right --> implicit op
left --> single value
"""
def __init__(self, left, operator=None, right=None):
self.left = left
self.operator = operator
self.right = right
def to_string(self):
# For debugging purposes
if self.right:
comps = [self.left.to_string()]
if self.operator:
comps.append(self.operator[1])
comps.append(self.right.to_string())
elif self.operator:
comps = [self.operator[1], self.left.to_string()]
else:
return self.left[1]
return "(%s)" % " ".join(comps)
[docs] def evaluate(self, define_op, bin_op=None, un_op=None):
"""Evaluate node.
Parameters
----------
define_op : callable
Translates tokens into objects.
bin_op : dict or None, optional
(Default value = _BINARY_OPERATOR_MAP)
un_op : dict or None, optional
(Default value = _UNARY_OPERATOR_MAP)
Returns
-------
"""
bin_op = bin_op or _BINARY_OPERATOR_MAP
un_op = un_op or _UNARY_OPERATOR_MAP
if self.right:
# binary or implicit operator
op_text = self.operator[1] if self.operator else ""
if op_text not in bin_op:
raise DefinitionSyntaxError('missing binary operator "%s"' % op_text)
left = self.left.evaluate(define_op, bin_op, un_op)
return bin_op[op_text](left, self.right.evaluate(define_op, bin_op, un_op))
elif self.operator:
# unary operator
op_text = self.operator[1]
if op_text not in un_op:
raise DefinitionSyntaxError('missing unary operator "%s"' % op_text)
return un_op[op_text](self.left.evaluate(define_op, bin_op, un_op))
else:
# single value
return define_op(self.left)
[docs]def build_eval_tree(tokens, op_priority=_OP_PRIORITY, index=0, depth=0, prev_op=None):
"""Build an evaluation tree from a set of tokens.
Params:
Index, depth, and prev_op used recursively, so don't touch.
Tokens is an iterable of tokens from an expression to be evaluated.
Transform the tokens from an expression into a recursive parse tree, following order
of operations. Operations can include binary ops (3 + 4), implicit ops (3 kg), or
unary ops (-1).
General Strategy:
1) Get left side of operator
2) If no tokens left, return final result
3) Get operator
4) Use recursion to create tree starting at token on right side of operator (start at step #1)
4.1) If recursive call encounters an operator with lower or equal priority to step #2, exit recursion
5) Combine left side, operator, and right side into a new left side
6) Go back to step #2
"""
if depth == 0 and prev_op is None:
# ensure tokens is list so we can access by index
tokens = list(tokens)
result = None
while True:
current_token = tokens[index]
token_type = current_token[0]
token_text = current_token[1]
if token_type == tokenlib.OP:
if token_text == ")":
if prev_op is None:
raise DefinitionSyntaxError(
"unopened parentheses in tokens: %s" % current_token
)
elif prev_op == "(":
# close parenthetical group
return result, index
else:
# parenthetical group ending, but we need to close sub-operations within group
return result, index - 1
elif token_text == "(":
# gather parenthetical group
right, index = build_eval_tree(
tokens, op_priority, index + 1, 0, token_text
)
if not tokens[index][1] == ")":
raise DefinitionSyntaxError("weird exit from parentheses")
if result:
# implicit op with a parenthetical group, i.e. "3 (kg ** 2)"
result = EvalTreeNode(left=result, right=right)
else:
# get first token
result = right
elif token_text in op_priority:
if result:
# equal-priority operators are grouped in a left-to-right order,
# unless they're exponentiation, in which case they're grouped
# right-to-left this allows us to get the expected behavior for
# multiple exponents
# (2^3^4) --> (2^(3^4))
# (2 * 3 / 4) --> ((2 * 3) / 4)
if op_priority[token_text] <= op_priority.get(
prev_op, -1
) and token_text not in ["**", "^"]:
# previous operator is higher priority, so end previous binary op
return result, index - 1
# get right side of binary op
right, index = build_eval_tree(
tokens, op_priority, index + 1, depth + 1, token_text
)
result = EvalTreeNode(
left=result, operator=current_token, right=right
)
else:
# unary operator
right, index = build_eval_tree(
tokens, op_priority, index + 1, depth + 1, "unary"
)
result = EvalTreeNode(left=right, operator=current_token)
elif token_type == tokenlib.NUMBER or token_type == tokenlib.NAME:
if result:
# tokens with an implicit operation i.e. "1 kg"
if op_priority[""] <= op_priority.get(prev_op, -1):
# previous operator is higher priority than implicit, so end
# previous binary op
return result, index - 1
right, index = build_eval_tree(
tokens, op_priority, index, depth + 1, ""
)
result = EvalTreeNode(left=result, right=right)
else:
# get first token
result = EvalTreeNode(left=current_token)
if tokens[index][0] == tokenlib.ENDMARKER:
if prev_op == "(":
raise DefinitionSyntaxError("unclosed parentheses in tokens")
if depth > 0 or prev_op:
# have to close recursion
return result, index
else:
# recursion all closed, so just return the final result
return result
if index + 1 >= len(tokens):
# should hit ENDMARKER before this ever happens
raise DefinitionSyntaxError("unexpected end to tokens")
index += 1
