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/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())