bpo-32678: inspect: Import ast lazily (GH-5344)

methane · web-flow · commit 37420deb80dc · 2018-01-27T10:10:06.000+09:00
diff --git a/Lib/inspect.py b/Lib/inspect.py
@@ -32,7 +32,6 @@
               'Yury Selivanov <yselivanov@sprymix.com>')
 
 import abc
-import ast
 import dis
 import collections.abc
 import enum
@@ -1940,6 +1939,9 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
     """Private helper to parse content of '__text_signature__'
     and return a Signature based on it.
     """
+    # Lazy import ast because it's relatively heavy and
+    # it's not used for other than this function.
+    import ast
 
     Parameter = cls._parameter_cls
 
