From 24b7682f6b36c74eb3e9baaa74d4eabf77143cff Mon Sep 17 00:00:00 2001
From: Rafal Skolasinski <r.j.skolasinski@gmail.com>
Date: Sun, 3 Dec 2017 12:13:09 +0100
Subject: [PATCH] continuum: check if symbol names are valid identifiers
A regression in Sympy causes symbols that are invalid
identifiers to be created, e.g. '-B_x'. While we cannot
fix Sympy's behaviour, we can at least shield our users
from its quirks.
Closes #179.
---
kwant/continuum/discretizer.py | 10 ++++++++++
kwant/continuum/tests/test_discretizer.py | 13 +++++++++++++
2 files changed, 23 insertions(+)
diff --git a/kwant/continuum/discretizer.py b/kwant/continuum/discretizer.py
index cac78399..119a4c11 100644
--- a/kwant/continuum/discretizer.py
+++ b/kwant/continuum/discretizer.py
@@ -6,6 +6,7 @@
# the file AUTHORS.rst at the top-level directory of this distribution and at
# http://kwant-project.org/authors.
+from keyword import iskeyword
from collections import defaultdict
import itertools
@@ -598,6 +599,15 @@ def _builder_value(expr, coords, grid_spacing, onsite,
# as arguments to the value function
arg_names = set.union({s.name for s in const_symbols},
{str(k.func) for k in map_func_calls})
+
+ # check if all argument names are valid python identifiers
+ for name in arg_names:
+ if not (name.isidentifier() and not iskeyword(name)):
+ raise ValueError("Invalid name in used symbols: {}\n"
+ "Names of symbols used in Hamiltonian "
+ "must be valid Python identifiers and "
+ "may not be keywords".format(name))
+
arg_names = ', '.join(sorted(arg_names))
if (not arg_names) and (coords is None):
diff --git a/kwant/continuum/tests/test_discretizer.py b/kwant/continuum/tests/test_discretizer.py
index 98a5cec8..47efbe3a 100644
--- a/kwant/continuum/tests/test_discretizer.py
+++ b/kwant/continuum/tests/test_discretizer.py
@@ -509,3 +509,16 @@ def test_numeric_functions_with_parameter():
rhs = f_num
assert np.allclose(lhs, rhs)
+
+
+@pytest.mark.parametrize('name', [
+ '1',
+ '1a',
+ '-a',
+ '+a',
+ 'while',
+ 'for'
+])
+def test_check_symbol_names(name):
+ with pytest.raises(ValueError):
+ discretize(sympy.Symbol(name), 'x')
--
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