diff --git a/pipreqs/pipreqs.py b/pipreqs/pipreqs.py
index 5cf763e..9a466f3 100755
--- a/pipreqs/pipreqs.py
+++ b/pipreqs/pipreqs.py
@@ -87,22 +87,22 @@ def get_all_imports(
             file_name = os.path.join(root, file_name)
             with open_func(file_name, "r", encoding=encoding) as f:
                 contents = f.read()
-                try:
-                    tree = ast.parse(contents)
-                    for node in ast.walk(tree):
-                        if isinstance(node, ast.Import):
-                            for subnode in node.names:
-                                raw_imports.add(subnode.name)
-                        elif isinstance(node, ast.ImportFrom):
-                            raw_imports.add(node.module)
-                except Exception as exc:
-                    if ignore_errors:
-                        traceback.print_exc(exc)
-                        logging.warn("Failed on file: %s" % file_name)
-                        continue
-                    else:
-                        logging.error("Failed on file: %s" % file_name)
-                        raise exc
+            try:
+                tree = ast.parse(contents)
+                for node in ast.walk(tree):
+                    if isinstance(node, ast.Import):
+                        for subnode in node.names:
+                            raw_imports.add(subnode.name)
+                    elif isinstance(node, ast.ImportFrom):
+                        raw_imports.add(node.module)
+            except Exception as exc:
+                if ignore_errors:
+                    traceback.print_exc(exc)
+                    logging.warn("Failed on file: %s" % file_name)
+                    continue
+                else:
+                    logging.error("Failed on file: %s" % file_name)
+                    raise exc
 
     # Clean up imports
     for name in [n for n in raw_imports if n]:
@@ -114,13 +114,14 @@ def get_all_imports(
         cleaned_name, _, _ = name.partition('.')
         imports.add(cleaned_name)
 
-    packages = set(imports) - set(set(candidates) & set(imports))
+    packages = imports - (set(candidates) & imports)
     logging.debug('Found packages: {0}'.format(packages))
 
     with open(join("stdlib"), "r") as f:
-        data = [x.strip() for x in f.readlines()]
-        data = [x for x in data if x not in py2_exclude] if py2 else data
-        return list(set(packages) - set(data))
+        data = {x.strip() for x in f}
+
+    data = {x for x in data if x not in py2_exclude} if py2 else data
+    return list(packages - data)
 
 
 def filter_line(l):