It works! Kind of.

README.md

-A generator for *Star Wars* interstellar shipping and passenger jobs, based loosely on the missions you can take on in *Escape Velocity* and *Endless Space*.
+A generator for *Star Wars* interstellar shipping and passenger jobs, based loosely on the missions you can take on in *Escape Velocity* and *Endless Sky*.
 
 
- SW Job Generator © 2023 by [Noëlle Anthony](https://chat.noelle.codes/@noelle) is licensed under [CC BY-NC-SA 4.0](http://creativecommons.org/licenses/by-nc-sa/4.0/?ref=chooser-v1) <img alt="Creative Commons logo" src="https://chooser-beta.creativecommons.org/img/cc-logo.f0ab4ebe.svg" height=20 style="max-height: 20px;" /> <img alt="cc-by symbol" src="https://chooser-beta.creativecommons.org/img/cc-by.21b728bb.svg" style="max-height: 20px;" height=20 />
+ SW Job Generator © 2023 by [Noëlle Anthony](https://chat.noelle.codes/@noelle) is licensed under [CC BY-NC-SA 4.0](http://creativecommons.org/licenses/by-nc-sa/4.0/?ref=chooser-v1) <img alt="Creative Commons logo" src="https://chooser-beta.creativecommons.org/img/cc-logo.f0ab4ebe.svg" height=16 style="max-height: 16px;" /> <img alt="cc-by symbol" src="https://chooser-beta.creativecommons.org/img/cc-by.21b728bb.svg" style="max-height: 16px;" height=16 />

swjg.py

+import argparse, re
+from string import Template
+from typing import NamedTuple
+
+from jinja2 import Environment, PackageLoader, select_autoescape
+
+# global variables
+
+env = Environment(
+    loader=PackageLoader("swjg"),
+    autoescape=select_autoescape
+)
+
+parser = argparse.ArgumentParser()
+
+# helper functions
+
+def get_identifiers_from_template(template):
+    # Template.get_identifiers() doesn't appear until Python 3.11
+
+    # Don't substitute anything; get the raw string
+    template_str = Template.safe_substitute()
+    matches = re.findall("\$[a-z0-9_\.]+", template_str)
+    matches = [x[1:] for x in matches]
+    return matches
+
+
+# classes and such
+
+class Destination(NamedTuple):
+    world: str
+    system: str|None
+    sector: str|None
+
+
+class Mission:
+    output_destination_template = Template("to $world in the $system system")
+    output_sector_template = Template(", part of the $sector,")
+    value_template = Template("for $value credits")
+    error_template = Template("You haven't given this mission some of the values it needs. Please check: $potential_values")
+
+    def __init__(self, destination:Destination, value:int, *args, **kwargs):
+        # destination: Destination (see above)
+        self.world = destination.world if destination.world is not None else None
+        self.system = destination.system if destination.system is not None else destination.world
+        self.sector = destination.sector if destination.sector is not None else None
+        self.value = value
+        # for arg, val in kwargs.items():
+        #     setattr(self, arg, val)
+
+    def assemble_templates(self) -> list:
+        # Override this in children
+        template_list = []
+        if self.world != None:
+            template_list.append(self.output_destination_template)
+        if self.sector != None:
+            template_list.append(self.output_sector_template)
+        template_list.append(self.value_template)
+        return template_list
+
+    def get_current_values(self) -> dict:
+        return {
+            "world": self.world,
+            "system": self.system,
+            "sector": self.sector,
+            "value": self.value
+        }
+
+    def missing_values(self) -> list:
+        object_vars = vars(self)
+        missing = []
+        for key, val in object_vars.items():
+            if val == None:
+                missing.append(key)
+        return missing
+
+    def assemble_text(self) -> str:
+        missing_vals = self.missing_values()
+        templates = self.assemble_templates()
+        if len(templates) == 0 or len(missing_vals) != 0: # either both of these should be true or neither should
+            raise ValueError(self.error_template.substitute(potential_values=missing_vals))
+
+        current_values = self.get_current_values()
+
+        output = []
+        for template in templates:
+            output.append(template.substitute(**current_values))
+        out_text = " ".join(output)
+        out_text = out_text.replace(" ,", ",")
+        out_text += "."
+        return out_text
+
+        
+class PassengerMission(Mission):
+    output_initial_template = Template("Bring $number passengers")
+
+    def __init__(self, number:int, *args, **kwargs):
+        super(PassengerMission, self).__init__(*args, **kwargs)
+        self.number = number
+
+    def get_current_values(self) -> dict:
+        base_dict = super(PassengerMission, self).get_current_values()
+        new_dict = {
+            "number": self.number
+        }
+        base_dict.update(new_dict)
+        return base_dict
+
+    def assemble_templates(self):
+        template_list = [self.output_initial_template]
+        template_list.extend(super(PassengerMission, self).assemble_templates())
+        return template_list
+
+    def assemble_text(self) -> str:
+        return super(PassengerMission, self).assemble_text()
+
+
+class CargoMission(Mission):
+    output_initial_template = Template("Deliver $tons tons of $item")
+    output_time_timeplate = Template("in the next $time days")
+
+    def __init__(self, tons:int, item:str, time:int, *args, **kwargs):
+        # tons: integer
+        # item: string (this will not be pluralized in the text)
+        # time: integer (number of days the crew have to complete delivery)
+        # value: integer (value in credits)
+        super(CargoMission, self).__init__(*args, **kwargs)
+        self.tons = tons
+        self.item = item
+        self.time = time
+
+    def get_current_values(self) -> dict:
+        base_dict = super(CargoMission, self).get_current_values()
+        new_dict = {
+            "tons": self.tons,
+            "item": self.item,
+            "time": self.time
+        }
+        base_dict.update(new_dict)
+        return base_dict
+
+    def assemble_templates(self):
+        template_list = [self.output_initial_template]
+        if self.time is not None:
+            template_list.append(self.output_time_timeplate)
+        template_list.extend(super(CargoMission, self).assemble_templates())
+        return template_list
+
+    def assemble_text(self) -> str:
+        return super(CargoMission, self).assemble_text()
+
+
+class GroupMission(Mission):
+    output_initial_template = Template("Bring $number members of a $group")
+
+    def __init__(self, number:int, group:str, *args, **kwargs):
+        super(GroupMission, self).__init__(*args, **kwargs)
+        self.number = number
+        self.group = group
+
+    def get_current_values(self) -> dict:
+        base_dict = super(GroupMission, self).get_current_values()
+        new_dict = {
+            "number": self.number,
+            "group": self.group
+        }
+        base_dict.update(new_dict)
+        return base_dict
+
+    def assemble_templates(self):
+        template_list = [self.output_initial_template]
+        template_list.extend(super(GroupMission, self).assemble_templates())
+        return template_list
+
+    def assemble_text(self) -> str:
+        return super(GroupMission, self).assemble_text()
+
+
+# the function that does the thing
+
+def main():
+    import random
+    mission_types = [PassengerMission, CargoMission, GroupMission]
+    missions = []
+    for _ in range(5):
+        current_mission = random.choice(mission_types)
+        destination = Destination("Alderaan", None, "Core Worlds")
+        number = random.randint(1,8)
+        tons = random.randint(4, 12)
+        item = random.choice(["gravel", "computer chips", "spice", "live ysalamiri", "empty shipping containers"])
+        time = random.randint(7, 31)
+        value = random.randint(20, 120) * 1000
+        group = None
+        if current_mission == GroupMission:
+            group = random.choice(["family", "performing troupe", "acrobatic troupe"])
+        missions.append(current_mission(destination=destination, number=number, tons=tons, item=item, time=time, value=value, group=group))
+    for mission in missions:
+        # print(mission, mission.__dict__)
+        print(mission.assemble_text())
+
+
+# Don't do anything if the module is loaded wholesale into something else
+
+if __name__ == "__main__":
+    main()