Add new checkers use-list-literal and use-dict-literal

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