[3.7] bpo-37163: dataclasses.replace() now supports the field named "obj". (GH-13877) (GH-14405)

(cherry picked from commit f5b89af)

Author: serhiy-storchaka

Lib/dataclasses.py

@@ -1202,7 +1202,7 @@ class C(Base):
  unsafe_hash=unsafe_hash, frozen=frozen)
 
 
-def replace(obj, **changes):
+def replace(*args, **changes):
  """Return a new object replacing specified fields with new values.
 
  This is especially useful for frozen classes. Example usage:
@@ -1216,6 +1216,14 @@ class C:
  c1 = replace(c, x=3)
  assert c1.x == 3 and c1.y == 2
  """
+ if len(args) > 1:
+ raise TypeError(f'replace() takes 1 positional argument but {len(args)} were given')
+ if args:
+ obj, = args
+ elif 'obj' in changes:
+ obj = changes.pop('obj')
+ else:
+ raise TypeError("replace() missing 1 required positional argument: 'obj'")
 
  # We're going to mutate 'changes', but that's okay because it's a
  # new dict, even if called with 'replace(obj, **my_changes)'.

Misc/NEWS.d/next/Library/2019-06-07-08-18-05.bpo-37163.36JkUh.rst

@@ -0,0 +1 @@
+:func:`dataclasses.replace` now supports the field named "obj".