Allow redefinition of Generators when in interactive mode (halide#7053)

It's really annoying to be using (e.g.) Colab/Jupyter/etc and get errors about "Generator already defined", so sniff for interactive mode and allow re-registration of the same name in that case.

python_bindings/src/halide/_generator_helpers.py

@@ -759,13 +759,30 @@ def active_generator_context() -> GeneratorContext:
  return context
 
 
+def _is_interactive_mode() -> bool:
+ return hasattr(sys, 'ps1')
+
+
+def _check_generator_name_in_use(n:str):
+ if _is_interactive_mode():
+ # In interactive mode, it's OK to redefine generators... in fact, it's really
+ # annoying not to allow this (e.g. in Colab)
+ #
+ # (Want to debug? Include this:)
+ # if n in _python_generators:
+ # builtins.print("REDEFINING ", n)
+ return
+
+ _check(n not in _python_generators, "The Generator name %s is already in use." % n)
+
+
 def alias(**kwargs):
 
  def alias_impl(cls):
  for k, v in kwargs.items():
  _check_valid_name(k)
  _check(hasattr(cls, "_halide_registered_name"), "@alias can only be used in conjunction with @generator.")
- _check(k not in _python_generators, "The Generator name %s is already in use." % k)
+ _check_generator_name_in_use(k)
  _check(type(v) is dict, "The Generator alias %s specifies something other than a dict." % k)
  new_cls = type(k, (cls,), {"_halide_registered_name": k, "_halide_alias_generator_params": v})
  _python_generators[k] = new_cls
@@ -779,7 +796,7 @@ def generator(name:str=""):
  _check(sys.version_info >= (3, 7), "Halide Generators require Python 3.7 or later.")
  def generator_impl(cls):
  n = name if name else _fqname(cls)
- _check(n not in _python_generators, "The Generator name %s is already in use." % n)
+ _check_generator_name_in_use(n)
  _check(isclass(cls), "@generator can only be used on classes.")
  # Allow (but don't require) explicit inheritance from hl.Generator;
  # static type checkers (e.g. pytype) can complain that the decorated class