in src/stepfunctions/inputs/placeholders.py [0:0]
def __getitem__(self, name):
"""
Subscript operator to build placeholder variables.
"""
if not self._is_valid_name(name):
raise ValueError('Key name can only be string or integer')
if name in self.store:
return self.store[name]
else:
self.store[name] = self._create_variable(name=name, parent=self)
return self.store[name]