Add new checkers use-list-literal and use-dict-literal (#4769)

* Add ``use-list-literal`` and ``use-dict-literal``
This adds two checks for when empty lists and dicts are created
using a function call instead of their literals.
This closes #4365

* Conform code to use-list-literal, use-dict-literal
With addition of the use-list-literal and use-dict-literal
checkers some code had to be updated.
As there is a real performance difference, the literal is preferred
when it is as clear as using the function call.

* Conform test to use-list-literal, use-dict-literal
With addition of the use-list-literal and use-dict-literal
checkers some code had to be updated.
As there is a real performance difference, the literal is preferred
when it is as clear as using the function call. For some tests
ignoring the checker seemed better for clarity of the test.

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>

ChangeLog

@@ -36,6 +36,14 @@ Release date: TBA
 
   Closes #3878
 
+* Added ``use-list-literal``: Emitted when ``list()`` is called with no arguments instead of using ``[]``
+
+  Closes #4365
+
+* Added ``use-dict-literal``: Emitted when ``dict()`` is called with no arguments instead of using ``{}``
+
+  Closes #4365
+
 * ``CodeStyleChecker``
 
   * Extended ``consider-using-tuple`` check to cover ``in`` comparisons.

doc/whatsnew/2.10.rst

@@ -16,6 +16,14 @@ New checkers
 
   Closes #3826
 
+* Added ``use-list-literal``: Emitted when ``list()`` is called with no arguments instead of using ``[]``
+
+  Closes #4365
+
+* Added ``use-dict-literal``: Emitted when ``dict()`` is called with no arguments instead of using ``{}``
+
+  Closes #4365
+
 
 Extensions
 ==========

pylint/checkers/refactoring/refactoring_checker.py

@@ -413,6 +413,18 @@ class RefactoringChecker(checkers.BaseTokenChecker):
             "value by index lookup. "
             "The value can be accessed directly instead.",
         ),
+        "R1734": (
+            "Consider using [] instead of list()",
+            "use-list-literal",
+            "Emitted when using list() to create an empty list instead of the literal []. "
+            "The literal is faster as it avoids an additional function call.",
+        ),
+        "R1735": (
+            "Consider using {} instead of dict()",
+            "use-dict-literal",
+            "Emitted when using dict() to create an empty dictionary instead of the literal {}. "
+            "The literal is faster as it avoids an additional function call.",
+        ),
     }
     options = (
         (
@@ -964,6 +976,8 @@ def _check_consider_using_generator(self, node):
         "super-with-arguments",
         "consider-using-generator",
         "consider-using-with",
+        "use-list-literal",
+        "use-dict-literal",
     )
     def visit_call(self, node):
         self._check_raising_stopiteration_in_generator_next_call(node)
@@ -972,6 +986,7 @@ def visit_call(self, node):
         self._check_super_with_arguments(node)
         self._check_consider_using_generator(node)
         self._check_consider_using_with(node)
+        self._check_use_list_or_dict_literal(node)
 
     @staticmethod
     def _has_exit_in_scope(scope):
@@ -1454,6 +1469,16 @@ def _check_consider_using_with(self, node: astroid.Call):
         if could_be_used_in_with and not _will_be_released_automatically(node):
             self.add_message("consider-using-with", node=node)
 
+    def _check_use_list_or_dict_literal(self, node: astroid.Call) -> None:
+        """Check if empty list or dict is created by using the literal [] or {}"""
+        if node.as_string() in ("list()", "dict()"):
+            inferred = utils.safe_infer(node.func)
+            if isinstance(inferred, astroid.ClassDef) and not node.args:
+                if inferred.qname() == "builtins.list":
+                    self.add_message("use-list-literal", node=node)
+                elif inferred.qname() == "builtins.dict" and not node.keywords:
+                    self.add_message("use-dict-literal", node=node)
+
     def _check_consider_using_join(self, aug_assign):
         """
         We start with the augmented assignment and work our way upwards.

pylint/checkers/stdlib.py

@@ -443,11 +443,11 @@ def __init__(self, linter=None):
         for since_vers, func_list in DEPRECATED_METHODS[sys.version_info[0]].items():
             if since_vers <= sys.version_info:
                 self._deprecated_methods.update(func_list)
-        self._deprecated_attributes = dict()
+        self._deprecated_attributes = {}
         for since_vers, func_list in DEPRECATED_ARGUMENTS.items():
             if since_vers <= sys.version_info:
                 self._deprecated_attributes.update(func_list)
-        self._deprecated_classes = dict()
+        self._deprecated_classes = {}
         for since_vers, class_list in DEPRECATED_CLASSES.items():
             if since_vers <= sys.version_info:
                 self._deprecated_classes.update(class_list)

pylint/checkers/utils.py

@@ -502,7 +502,7 @@ def parse_format_string(
     IncompleteFormatString or UnsupportedFormatCharacter if a
     parse error occurs."""
     keys = set()
-    key_types = dict()
+    key_types = {}
     pos_types = []
     num_args = 0
 

pylint/utils/pragma_parser.py

@@ -116,7 +116,7 @@ def parse_pragma(pylint_pragma: str) -> Generator[PragmaRepresenter, None, None]
             if action:
                 yield emit_pragma_representer(action, messages)
             action = value
-            messages = list()
+            messages = []
             assignment_required = action in MESSAGE_KEYWORDS
         elif kind in ("MESSAGE_STRING", "MESSAGE_NUMBER"):
             messages.append(value)

tests/functional/c/consider/consider_using_dict_comprehension.py

@@ -1,4 +1,4 @@
-# pylint: disable=missing-docstring, invalid-name
+# pylint: disable=missing-docstring, invalid-name, use-dict-literal
 
 numbers = [1, 2, 3, 4, 5, 6]
 

tests/functional/c/consider/consider_using_dict_items.py

@@ -1,5 +1,5 @@
 """Emit a message for iteration through dict keys and subscripting dict with key."""
-# pylint: disable=line-too-long,missing-docstring,unsubscriptable-object,too-few-public-methods,redefined-outer-name
+# pylint: disable=line-too-long,missing-docstring,unsubscriptable-object,too-few-public-methods,redefined-outer-name,use-dict-literal
 
 def bad():
     a_dict = {1: 1, 2: 2, 3: 3}

tests/functional/c/consider/consider_using_get.py

@@ -1,5 +1,5 @@
 # pylint: disable=missing-docstring,invalid-name,using-constant-test,invalid-sequence-index,undefined-variable
-dictionary = dict()
+dictionary = {}
 key = 'key'
 
 if 'key' in dictionary:  # [consider-using-get]

tests/functional/d/dangerous_default_value_py30.py

@@ -1,4 +1,4 @@
-# pylint: disable=missing-docstring
+# pylint: disable=missing-docstring, use-list-literal, use-dict-literal
 import collections
 
 HEHE = {}

tests/functional/g/generic_alias/generic_alias_side_effects.py

@@ -1,4 +1,4 @@
-# pylint: disable=missing-docstring,invalid-name,line-too-long,too-few-public-methods
+# pylint: disable=missing-docstring,invalid-name,line-too-long,too-few-public-methods,use-list-literal,use-dict-literal
 import typing
 import collections
 from typing import Generic, TypeVar

tests/functional/i/invalid/e/invalid_exceptions_caught.py

@@ -1,4 +1,4 @@
-# pylint: disable=missing-docstring, too-few-public-methods, useless-object-inheritance
+# pylint: disable=missing-docstring, too-few-public-methods, useless-object-inheritance, use-list-literal
 # pylint: disable=too-many-ancestors, no-absolute-import, import-error, multiple-imports,wrong-import-position
 from __future__ import print_function
 

tests/functional/i/invalid/g/invalid_getnewargs_ex_returned.py

@@ -1,6 +1,6 @@
 """Check invalid value returned by __getnewargs_ex__ """
 
-# pylint: disable=too-few-public-methods,missing-docstring,no-self-use,import-error, useless-object-inheritance
+# pylint: disable=too-few-public-methods,missing-docstring,no-self-use,import-error, useless-object-inheritance, use-dict-literal
 import six
 
 from missing import Missing

tests/functional/i/invalid/invalid_unary_operand_type.py

@@ -1,6 +1,6 @@
 """Detect problems with invalid operands used on invalid objects."""
 # pylint: disable=missing-docstring,too-few-public-methods,invalid-name
-# pylint: disable=unused-variable, useless-object-inheritance
+# pylint: disable=unused-variable, useless-object-inheritance, use-dict-literal
 
 import collections
 

tests/functional/n/not_callable.py

@@ -1,4 +1,4 @@
-# pylint: disable=missing-docstring,no-self-use,too-few-public-methods,wrong-import-position, useless-object-inheritance
+# pylint: disable=missing-docstring,no-self-use,too-few-public-methods,wrong-import-position,useless-object-inheritance,use-dict-literal
 
 REVISION = None
 

tests/functional/s/statement_without_effect.py

@@ -1,5 +1,5 @@
 """Test for statements without effects."""
-# pylint: disable=too-few-public-methods, useless-object-inheritance, unnecessary-comprehension
+# pylint: disable=too-few-public-methods, useless-object-inheritance, unnecessary-comprehension, use-list-literal
 
 # +1:[pointless-string-statement]
 """inline doc string should use a separated message"""

tests/functional/u/unnecessary/unnecessary_comprehension.py

@@ -13,7 +13,7 @@
 [2 * x for x in iterable]  # exclude useful comprehensions
 [(x, y, 1) for x, y in iterable]  # exclude useful comprehensions
 # Test case for issue #4499
-a_dict = dict()
+a_dict = {}
 [(k, v) for k, v in a_dict.items()]  # [unnecessary-comprehension]
 
 # Set comprehensions
@@ -39,8 +39,8 @@
 {2 * x: 3 + x for x in iterable}  # exclude useful comprehensions
 
 # Some additional tests on helptext -- when object is already a list/set/dict
-my_list = list()
-my_dict = dict()
+my_list = []
+my_dict = {}
 my_set = set()
 
 [elem for elem in my_list]  # [unnecessary-comprehension]

tests/functional/u/unnecessary/unnecessary_dict_index_lookup.py

@@ -1,7 +1,7 @@
 # pylint: disable=missing-docstring, too-few-public-methods, expression-not-assigned, line-too-long
 
-a_dict = dict()
-b_dict = dict()
+a_dict = {}
+b_dict = {}
 
 for k, v in a_dict.items():
     print(a_dict[k])  # [unnecessary-dict-index-lookup]

tests/functional/u/unnecessary/unnecessary_lambda.py

@@ -1,4 +1,4 @@
-# pylint: disable=undefined-variable
+# pylint: disable=undefined-variable, use-list-literal
 """test suspicious lambda expressions
 """
 

tests/functional/u/use/use_literal_dict.py

@@ -0,0 +1,7 @@
+# pylint: disable=missing-docstring, invalid-name
+
+x = dict()  # [use-dict-literal]
+x = dict(a="1", b=None, c=3)
+x = dict(zip(["a", "b", "c"], [1, 2, 3]))
+x = {}
+x = {"a": 1, "b": 2, "c": 3}

tests/functional/u/use/use_literal_dict.txt

@@ -0,0 +1 @@
+use-dict-literal:3:4::"Consider using {} instead of dict()"

tests/functional/u/use/use_literal_list.py

@@ -0,0 +1,9 @@
+# pylint: disable=missing-docstring, invalid-name
+
+x = list()  # [use-list-literal]
+x = list("string")
+x = list(range(3))
+x = []
+x = ["string"]
+x = [1, 2, 3]
+x = [range(3)]

tests/functional/u/use/use_literal_list.txt

@@ -0,0 +1 @@
+use-list-literal:3:4::"Consider using [] instead of list()"

tests/functional/u/use/using_constant_test.py

@@ -2,7 +2,7 @@
 # pylint: disable=invalid-name, missing-docstring,too-few-public-methods
 # pylint: disable=no-init,expression-not-assigned, useless-object-inheritance
 # pylint: disable=missing-parentheses-for-call-in-test, unnecessary-comprehension, condition-evals-to-constant
-
+# pylint: disable=use-list-literal, use-dict-literal
 
 import collections