Get PEP 440 dependency requirements for a craft spec.

specstr, sktime/skbase compatible object specification

i.e., a string that executes to construct an object if all imports were present imports inferred are of any classes in the scope of all_estimators option 1: a string that evaluates to an estimator option 2: a sequence of assignments in valid python code,

with the object to be defined preceded by a “return” assignments can use names of classes as if all imports were present

reqslist of str

each str is PEP 440 compatible requirement string for craft(spec) if spec has no requirements, return is [], the length 0 list