Add check to enforce literal syntax for Python builtin types

This check requires authors to initialize empty or zero builtin types
using the literal syntax (e.g., `{}` instead of `dict()`).

Authors may ignore this requirement for certain builtins using the
`--ignore` option.

Authors may also forbid calling `dict()` with keyword arguments
(`dict(a=1, b=2)`) using the `--no-allow-dict-kwargs` flag.

.pre-commit-hooks.yaml

@@ -34,6 +34,15 @@
     # for backward compatibility
     files: ''
     minimum_pre_commit_version: 0.15.0
+-   id: check-builtin-literals
+    name: Check builtin type constructor use
+    description: Require literal syntax when initializing empty or zero Python builtin types.
+    entry: check-builtin-literals
+    language: python
+    types: [python]
+    # for backward compatibility
+    files: ''
+    minimum_pre_commit_version: 0.15.0
 -   id: check-case-conflict
     name: Check for case conflicts
     description: Check for files that would conflict in case-insensitive filesystems

README.md

@@ -30,6 +30,10 @@ Add this to your `.pre-commit-config.yaml`
 - `check-added-large-files` - Prevent giant files from being committed.
     - Specify what is "too large" with `args: ['--maxkb=123']` (default=500kB).
 - `check-ast` - Simply check whether files parse as valid python.
+- `check-builtin-literals` - Require literal syntax when initializing empty or zero Python builtin types.
+    - Allows calling constructors with positional arguments (e.g., `list('abc')`).
+    - Ignore this requirement for specific builtin types with `--ignore=type1,type2,…`.
+    - Forbid `dict` keyword syntax with `--no-allow-dict-kwargs`.
 - `check-byte-order-marker` - Forbid files which have a UTF-8 byte-order marker
 - `check-case-conflict` - Check for files with names that would conflict on a
   case-insensitive filesystem like MacOS HFS+ or Windows FAT.

hooks.yaml

@@ -16,6 +16,12 @@
     entry: upgrade-your-pre-commit-version
     files: ''
     minimum_pre_commit_version: 0.15.0
+-   id: check-builtin-literals
+    language: system
+    name: upgrade-your-pre-commit-version
+    entry: upgrade-your-pre-commit-version
+    files: ''
+    minimum_pre_commit_version: 0.15.0
 -   id: check-byte-order-marker
     language: system
     name: upgrade-your-pre-commit-version

pre_commit_hooks/check_builtin_literals.py

@@ -0,0 +1,90 @@
+from __future__ import unicode_literals
+
+import argparse
+import ast
+import collections
+import sys
+
+
+BUILTIN_TYPES = {
+    'complex': '0j',
+    'dict': '{}',
+    'float': '0.0',
+    'int': '0',
+    'list': '[]',
+    'str': "''",
+    'tuple': '()',
+}
+
+
+BuiltinTypeCall = collections.namedtuple('BuiltinTypeCall', ['name', 'line', 'column'])
+
+
+class BuiltinTypeVisitor(ast.NodeVisitor):
+    def __init__(self, ignore=None, allow_dict_kwargs=True):
+        self.builtin_type_calls = []
+        self.ignore = set(ignore) if ignore else set()
+        self.allow_dict_kwargs = allow_dict_kwargs
+
+    def _check_dict_call(self, node):
+        return self.allow_dict_kwargs and (getattr(node, 'kwargs', None) or getattr(node, 'keywords', None))
+
+    def visit_Call(self, node):
+        if node.func.id not in set(BUILTIN_TYPES).difference(self.ignore):
+            return
+        if node.func.id == 'dict' and self._check_dict_call(node):
+            return
+        elif node.args:
+            return
+        self.builtin_type_calls.append(
+            BuiltinTypeCall(node.func.id, node.lineno, node.col_offset),
+        )
+
+
+def check_file_for_builtin_type_constructors(filename, ignore=None, allow_dict_kwargs=True):
+    tree = ast.parse(open(filename, 'rb').read(), filename=filename)
+    visitor = BuiltinTypeVisitor(ignore=ignore, allow_dict_kwargs=allow_dict_kwargs)
+    visitor.visit(tree)
+    return visitor.builtin_type_calls
+
+
+def parse_args(argv):
+    def parse_ignore(value):
+        return set(value.split(','))
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='*')
+    parser.add_argument('--ignore', type=parse_ignore, default=set())
+
+    allow_dict_kwargs = parser.add_mutually_exclusive_group(required=False)
+    allow_dict_kwargs.add_argument('--allow-dict-kwargs', action='store_true')
+    allow_dict_kwargs.add_argument('--no-allow-dict-kwargs', dest='allow_dict_kwargs', action='store_false')
+    allow_dict_kwargs.set_defaults(allow_dict_kwargs=True)
+
+    return parser.parse_args(argv)
+
+
+def main(argv=None):
+    args = parse_args(argv)
+    rc = 0
+    for filename in args.filenames:
+        calls = check_file_for_builtin_type_constructors(
+            filename,
+            ignore=args.ignore,
+            allow_dict_kwargs=args.allow_dict_kwargs,
+        )
+        if calls:
+            rc = rc or 1
+        for call in calls:
+            print(
+                '{filename}:{call.line}:{call.column} - Replace {call.name}() with {replacement}'.format(
+                    filename=filename,
+                    call=call,
+                    replacement=BUILTIN_TYPES[call.name],
+                ),
+            )
+    return rc
+
+
+if __name__ == '__main__':
+    sys.exit(main())

setup.py

@@ -36,6 +36,7 @@ setup(
             'autopep8-wrapper = pre_commit_hooks.autopep8_wrapper:main',
             'check-added-large-files = pre_commit_hooks.check_added_large_files:main',
             'check-ast = pre_commit_hooks.check_ast:check_ast',
+            'check-builtin-literals = pre_commit_hooks.check_builtin_literals:main',
             'check-byte-order-marker = pre_commit_hooks.check_byte_order_marker:main',
             'check-case-conflict = pre_commit_hooks.check_case_conflict:main',
             'check-docstring-first = pre_commit_hooks.check_docstring_first:main',

testing/resources/builtin_constructors.py

@@ -0,0 +1,7 @@
+c1 = complex()
+d1 = dict()
+f1 = float()
+i1 = int()
+l1 = list()
+s1 = str()
+t1 = tuple()

testing/resources/builtin_literals.py

@@ -0,0 +1,7 @@
+c1 = 0j
+d1 = {}
+f1 = 0.0
+i1 = 0
+l1 = []
+s1 = ''
+t1 = ()

tests/check_builtin_literals_test.py

@@ -0,0 +1,107 @@
+import ast
+
+import pytest
+
+from pre_commit_hooks.check_builtin_literals import BuiltinTypeCall
+from pre_commit_hooks.check_builtin_literals import BuiltinTypeVisitor
+from pre_commit_hooks.check_builtin_literals import main
+from testing.util import get_resource_path
+
+
+@pytest.fixture
+def visitor():
+    return BuiltinTypeVisitor()
+
+
+@pytest.mark.parametrize(
+    ('expression', 'calls'),
+    [
+        # complex
+        ("0j", []),
+        ("complex()", [BuiltinTypeCall('complex', 1, 0)]),
+        ("complex(0, 0)", []),
+        ("complex('0+0j')", []),
+        # float
+        ("0.0", []),
+        ("float()", [BuiltinTypeCall('float', 1, 0)]),
+        ("float('0.0')", []),
+        # int
+        ("0", []),
+        ("int()", [BuiltinTypeCall('int', 1, 0)]),
+        ("int('0')", []),
+        # list
+        ("[]", []),
+        ("list()", [BuiltinTypeCall('list', 1, 0)]),
+        ("list('abc')", []),
+        ("list([c for c in 'abc'])", []),
+        ("list(c for c in 'abc')", []),
+        # str
+        ("''", []),
+        ("str()", [BuiltinTypeCall('str', 1, 0)]),
+        ("str('0')", []),
+        ("[]", []),
+        # tuple
+        ("()", []),
+        ("tuple()", [BuiltinTypeCall('tuple', 1, 0)]),
+        ("tuple('abc')", []),
+        ("tuple([c for c in 'abc'])", []),
+        ("tuple(c for c in 'abc')", []),
+    ],
+)
+def test_non_dict_exprs(visitor, expression, calls):
+    visitor.visit(ast.parse(expression))
+    assert visitor.builtin_type_calls == calls
+
+
+@pytest.mark.parametrize(
+    ('expression', 'calls'),
+    [
+        ("{}", []),
+        ("dict()", [BuiltinTypeCall('dict', 1, 0)]),
+        ("dict(a=1, b=2, c=3)", []),
+        ("dict(**{'a': 1, 'b': 2, 'c': 3})", []),
+        ("dict([(k, v) for k, v in [('a', 1), ('b', 2), ('c', 3)]])", []),
+        ("dict((k, v) for k, v in [('a', 1), ('b', 2), ('c', 3)])", []),
+    ],
+)
+def test_dict_allow_kwargs_exprs(visitor, expression, calls):
+    visitor.visit(ast.parse(expression))
+    assert visitor.builtin_type_calls == calls
+
+
+@pytest.mark.parametrize(
+    ('expression', 'calls'),
+    [
+        ("dict()", [BuiltinTypeCall('dict', 1, 0)]),
+        ("dict(a=1, b=2, c=3)", [BuiltinTypeCall('dict', 1, 0)]),
+        ("dict(**{'a': 1, 'b': 2, 'c': 3})", [BuiltinTypeCall('dict', 1, 0)]),
+    ],
+)
+def test_dict_no_allow_kwargs_exprs(expression, calls):
+    visitor = BuiltinTypeVisitor(allow_dict_kwargs=False)
+    visitor.visit(ast.parse(expression))
+    assert visitor.builtin_type_calls == calls
+
+
+def test_ignore_constructors():
+    visitor = BuiltinTypeVisitor(ignore=('complex', 'dict', 'float', 'int', 'list', 'str', 'tuple'))
+    visitor.visit(ast.parse(open(get_resource_path('builtin_constructors.py'), 'rb').read(), 'builtin_constructors.py'))
+    assert visitor.builtin_type_calls == []
+
+
+def test_failing_file():
+    rc = main([get_resource_path('builtin_constructors.py')])
+    assert rc == 1
+
+
+def test_passing_file():
+    rc = main([get_resource_path('builtin_literals.py')])
+    assert rc == 0
+
+
+def test_failing_file_ignore_all():
+    rc = main([
+        '--ignore=complex,dict,float,int,list,str,tuple',
+        get_resource_path('builtin_constructors.py'),
+    ])
+    assert rc == 0