fix: don't count '=' inside string literals when parsing parameters

PythonTranslator.inspect treated any line with more than one '=' as
unparseable, which incorrectly rejected parameter lines like
s = "a=b" where the second '=' is inside a string literal.

Count only top-level assignment operators using tokenize so the
existing PARAMETER_PATTERN regex (which already handles '=' in values
correctly) is given a chance to match.

Closes #864

Author: SAY-5

papermill/tests/test_translators.py

@@ -107,6 +107,9 @@ def test_translate_comment_python(test_input, expected):
                 Parameter("b", "float", "-2.3432", "My b variable"),
             ],
         ),
+        # Regression test for #864: '=' inside string literals shouldn't trip parsing.
+        ('s = "a=b"', [Parameter("s", "None", '"a=b"', "")]),
+        ("s = 'a=b'", [Parameter("s", "None", "'a=b'", "")]),
     ],
 )
 def test_inspect_python(test_input, expected):

papermill/translators.py

@@ -1,14 +1,33 @@
+import io
 import logging
 import math
 import re
 import shlex
+import tokenize
 
 from .exceptions import PapermillException
 from .models import Parameter
 
 logger = logging.getLogger(__name__)
 
 
+def _count_assignment_operators(line):
+    """Count top-level assignment operators in a Python source line.
+
+    Uses ``tokenize`` so that ``=`` characters appearing inside string
+    literals (e.g. ``s = "a=b"``) are not counted as assignment
+    operators. Falls back to a naive ``line.count('=')`` if tokenization
+    fails (e.g. for incomplete multiline definitions).
+    """
+    try:
+        tokens = tokenize.tokenize(io.BytesIO(line.encode("utf-8")).readline)
+        return sum(
+            1 for tok in tokens if tok.type == tokenize.OP and tok.string == "="
+        )
+    except (tokenize.TokenError, SyntaxError):
+        return line.count("=")
+
+
 class PapermillTranslators:
     '''
     The holder which houses any translator registered with the system.
@@ -242,7 +261,7 @@ def flatten_accumulator(accumulator):
             if len(line.strip()) == 0 or line.strip().startswith('#'):
                 continue  # Skip blank and comment
 
-            nequal = line.count("=")
+            nequal = _count_assignment_operators(line)
             if nequal > 0:
                 grouped_variable.append(flatten_accumulator(accumulator))
                 accumulator = []