New scripts folder to check the effectiveness of fixers

check/README.md

+These scripts are used to manually check that the fixers have not forgotten any
+special cases, i.e. the implementation of their `match` method is good enough.

check/trace_division.py

+import ast, os, sys
+
+
+class Analyzer(ast.NodeVisitor):
+  def __init__(self, file_path):
+    with open(file_path) as f:
+      source_code = f.read()
+      self.file_path = f.name
+    self.source_code = source_code.split('\n')
+    self.tree = ast.parse(source_code)
+    self.warnings = 0
+
+  def __call__(self):
+    self.visit(self.tree)
+    return self.warnings
+
+  def visit_BinOp(self, node):
+    if isinstance(node.op, ast.Div):
+      self.warnings += 1
+      print("%s:%s |%s" % (
+        self.file_path, node.lineno, self.source_code[node.lineno - 1]))
+
+
+def analyze_file(file_path):
+  try:
+    analyzer = Analyzer(file_path)
+  except Exception as e:
+    print("Error: %s => %s" % (file_path, e))
+    return 0, 1
+  return analyzer(), 0
+
+
+def analyze_dir(dir_path):
+  total_warnings = total_errors = 0
+  # Inspired by lib2to3
+  py_ext = os.extsep + "py"
+  for dirpath, dirnames, filenames in os.walk(dir_path):
+    for name in filenames:
+      if not name.startswith(".") and os.path.splitext(name)[1] == py_ext:
+        warnings, errors = analyze_file(os.path.join(dirpath, name))
+        total_warnings += warnings
+        total_errors += errors
+  return total_warnings, total_errors
+
+
+def main():
+  for dir_or_file in sys.argv[1:]:
+    f = analyze_dir if os.path.isdir(dir_or_file) else analyze_file
+    print("%s warning(s), %s error(s)" % f(dir_or_file))
+
+
+if __name__ == '__main__':
+  main()