Separate string and bytes classes patching (pylint-dev#807)

Fixes pylint-dev/pylint#3599

Author: PCManticore

ChangeLog

@@ -9,6 +9,10 @@ Release Date: TBA
 
 * Added a brain for ``sqlalchemy.orm.session``
 
+* Separate string and bytes classes patching
+
+  Fixes PyCQA/pylint#3599
+
 * Added missing methods to the brain for ``mechanize``, to fix pylint false positives
 
   Close #793

astroid/brain/brain_builtin_inference.py

@@ -40,52 +40,90 @@
 
 OBJECT_DUNDER_NEW = "object.__new__"
 
-
-def _extend_str(class_node, rvalue):
+STR_CLASS = """
+class whatever(object):
+    def join(self, iterable):
+        return {rvalue}
+    def replace(self, old, new, count=None):
+        return {rvalue}
+    def format(self, *args, **kwargs):
+        return {rvalue}
+    def encode(self, encoding='ascii', errors=None):
+        return b''
+    def decode(self, encoding='ascii', errors=None):
+        return u''
+    def capitalize(self):
+        return {rvalue}
+    def title(self):
+        return {rvalue}
+    def lower(self):
+        return {rvalue}
+    def upper(self):
+        return {rvalue}
+    def swapcase(self):
+        return {rvalue}
+    def index(self, sub, start=None, end=None):
+        return 0
+    def find(self, sub, start=None, end=None):
+        return 0
+    def count(self, sub, start=None, end=None):
+        return 0
+    def strip(self, chars=None):
+        return {rvalue}
+    def lstrip(self, chars=None):
+        return {rvalue}
+    def rstrip(self, chars=None):
+        return {rvalue}
+    def rjust(self, width, fillchar=None):
+        return {rvalue}
+    def center(self, width, fillchar=None):
+        return {rvalue}
+    def ljust(self, width, fillchar=None):
+        return {rvalue}
+"""
+
+
+BYTES_CLASS = """
+class whatever(object):
+    def join(self, iterable):
+        return {rvalue}
+    def replace(self, old, new, count=None):
+        return {rvalue}
+    def decode(self, encoding='ascii', errors=None):
+        return u''
+    def capitalize(self):
+        return {rvalue}
+    def title(self):
+        return {rvalue}
+    def lower(self):
+        return {rvalue}
+    def upper(self):
+        return {rvalue}
+    def swapcase(self):
+        return {rvalue}
+    def index(self, sub, start=None, end=None):
+        return 0
+    def find(self, sub, start=None, end=None):
+        return 0
+    def count(self, sub, start=None, end=None):
+        return 0
+    def strip(self, chars=None):
+        return {rvalue}
+    def lstrip(self, chars=None):
+        return {rvalue}
+    def rstrip(self, chars=None):
+        return {rvalue}
+    def rjust(self, width, fillchar=None):
+        return {rvalue}
+    def center(self, width, fillchar=None):
+        return {rvalue}
+    def ljust(self, width, fillchar=None):
+        return {rvalue}
+"""
+
+
+def _extend_string_class(class_node, code, rvalue):
     """function to extend builtin str/unicode class"""
-    code = dedent(
-        """
-    class whatever(object):
-        def join(self, iterable):
-            return {rvalue}
-        def replace(self, old, new, count=None):
-            return {rvalue}
-        def format(self, *args, **kwargs):
-            return {rvalue}
-        def encode(self, encoding='ascii', errors=None):
-            return ''
-        def decode(self, encoding='ascii', errors=None):
-            return u''
-        def capitalize(self):
-            return {rvalue}
-        def title(self):
-            return {rvalue}
-        def lower(self):
-            return {rvalue}
-        def upper(self):
-            return {rvalue}
-        def swapcase(self):
-            return {rvalue}
-        def index(self, sub, start=None, end=None):
-            return 0
-        def find(self, sub, start=None, end=None):
-            return 0
-        def count(self, sub, start=None, end=None):
-            return 0
-        def strip(self, chars=None):
-            return {rvalue}
-        def lstrip(self, chars=None):
-            return {rvalue}
-        def rstrip(self, chars=None):
-            return {rvalue}
-        def rjust(self, width, fillchar=None):
-            return {rvalue}
-        def center(self, width, fillchar=None):
-            return {rvalue}
-        def ljust(self, width, fillchar=None):
-            return {rvalue}
-    """
-    )
     code = code.format(rvalue=rvalue)
     fake = AstroidBuilder(MANAGER).string_build(code)["whatever"]
     for method in fake.mymethods():
@@ -106,8 +144,8 @@ def _extend_builtins(class_transforms):
 
 _extend_builtins(
     {
-        "bytes": partial(_extend_str, rvalue="b''"),
-        "str": partial(_extend_str, rvalue="''"),
+        "bytes": partial(_extend_string_class, code=BYTES_CLASS, rvalue="b''"),
+        "str": partial(_extend_string_class, code=STR_CLASS, rvalue="''"),
     }
 )
 

tests/unittest_brain.py

@@ -2020,5 +2020,20 @@ class Other:
     assert isinstance(name[0], astroid.Unknown)
 
 
+@pytest.mark.parametrize(
+    "code,expected_class,expected_value",
+    [
+        ("'hey'.encode()", astroid.Const, b""),
+        ("b'hey'.decode()", astroid.Const, ""),
+        ("'hey'.encode().decode()", astroid.Const, ""),
+    ],
+)
+def test_str_and_bytes(code, expected_class, expected_value):
+    node = astroid.extract_node(code)
+    inferred = next(node.infer())
+    assert isinstance(inferred, expected_class)
+    assert inferred.value == expected_value
+
+
 if __name__ == "__main__":
     unittest.main()

tests/unittest_inference.py

@@ -2083,8 +2083,6 @@ def test_dict_invalid_args(self):
     def test_str_methods(self):
         code = """
         ' '.decode() #@
-
-        ' '.encode() #@
         ' '.join('abcd') #@
         ' '.replace('a', 'b') #@
         ' '.format('a') #@
@@ -2106,15 +2104,13 @@ def test_str_methods(self):
         """
         ast = extract_node(code, __name__)
         self.assertInferConst(ast[0], "")
-        for i in range(1, 16):
+        for i in range(1, 15):
             self.assertInferConst(ast[i], "")
-        for i in range(16, 19):
+        for i in range(15, 18):
             self.assertInferConst(ast[i], 0)
 
     def test_unicode_methods(self):
         code = """
-        u' '.encode() #@
-
         u' '.decode() #@
         u' '.join('abcd') #@
         u' '.replace('a', 'b') #@
@@ -2137,9 +2133,9 @@ def test_unicode_methods(self):
         """
         ast = extract_node(code, __name__)
         self.assertInferConst(ast[0], "")
-        for i in range(1, 16):
+        for i in range(1, 15):
             self.assertInferConst(ast[i], "")
-        for i in range(16, 19):
+        for i in range(15, 18):
             self.assertInferConst(ast[i], 0)
 
     def test_scope_lookup_same_attributes(self):