from pyparsing import (
CharsNotIn,
Combine,
Optional,
ParseException,
Regex,
Suppress,
Word,
alphas,
nums,
)
from brian2.utils.caching import cached
VARIABLE = Word(f"{alphas}_", f"{alphas + nums}_").setResultsName("variable")
OP = Regex(r"(\+|\-|\*|/|//|%|\*\*|>>|<<|&|\^|\|)?=").setResultsName("operation")
EXPR = Combine(
CharsNotIn("=", min=1, max=1) + Optional(CharsNotIn("#"))
).setResultsName("expression")
COMMENT = Optional(CharsNotIn("#")).setResultsName("comment")
STATEMENT = VARIABLE + OP + EXPR + Optional(Suppress("#") + COMMENT)
[docs]
@cached
def parse_statement(code):
"""
parse_statement(code)
Parses a single line of code into "var op expr".
Parameters
----------
code : str
A string containing a single statement of the form
``var op expr # comment``, where the ``# comment`` part is optional.
Returns
-------
var, op, expr, comment : str, str, str, str
The four parts of the statement.
Examples
--------
>>> parse_statement('v = -65*mV # reset the membrane potential')
('v', '=', '-65*mV', 'reset the membrane potential')
>>> parse_statement('v += dt*(-v/tau)')
('v', '+=', 'dt*(-v/tau)', '')
"""
try:
parsed = STATEMENT.parseString(code, parseAll=True)
except ParseException as p_exc:
raise ValueError(
"Parsing the statement failed: \n"
+ str(p_exc.line)
+ "\n"
+ " " * (p_exc.column - 1)
+ "^\n"
+ str(p_exc)
)
parsed_statement = (
parsed["variable"].strip(),
parsed["operation"],
parsed["expression"].strip(),
parsed.get("comment", "").strip(),
)
return parsed_statement