An example of proper handling of pronoun replacement for, e.g., text games.

pronouns.py

################################################################
# pronouns.py - Leonora Tindall     
# 
# An example of proper handling of pronoun replacement in
#   Python, including a selection menu. This handles only
#   singular pronouns, providing a simple .format() based
#   interface for replacing pronouns in prose. 
# This script is limited to English, but a similar technique
#   should work for most languages using a similar grammar.
################################################################


class UnknownBuiltinPronounException(Exception):
    pass

class MissingRequiredPronounException(Exception):
    pass

class Pronouns:
    built_in_sets = {"he": ("him", "his", "his", "himself"),
            "she": ("her", "her", "hers", "herself"),
            "they": ("them", "their", "theirs", "themself")}

    def __init__(self, subjective, objective=None, dep_posessive=None, 
            indep_posessive=None, reflexive=None):

        if objective is None:
            if subjective in self.built_in_sets.keys():
                self.subjective = subjective,
                self.objective, self.dep_posessive, self.indep_posessive, self.reflexive = self.built_in_sets[subjective]
                return 
            raise UnknownBuiltinPronounException
        elif dep_posessive is None:
            raise MissingRequiredPronounException("A dependent posessive pronoun " 
                    "is required.")
        
        # The required pronouns (dependent posessive, objective, and subjective) 
        # are fulfilled, and the object hasn't been constructed based on a builtin set.
        self.subjective = subjective
        self.objective = objective
        self.dep_posessive = dep_posessive
        if reflexive is None:
            self.reflexive = "{}self".format(self.objective)
        else:
            self.reflexive = reflexive
        if indep_posessive is None:
            self.indep_posessive = "{}s".format(dep_posessive)
        else:
            self.indep_posessive = indep_posessive



# This method asks the user to enter custom pronouns. If given three, it assumed they are
#   subjective, objective, and dependent posessive, and the function will guess the 
#   independent posessive and reflexive forms
def get_custom_pronouns():
    print("Enter pronouns, space separated.") 
    print("Examples: they them their; she her her hers herself: ")
    pronouns = input("Enter: ").split()

    if len(pronouns) == 3:   
        return Pronouns(pronouns[0], pronouns[1], pronouns[2])
    # With five given pronouns, the function just fills them in
    elif len(pronouns) == 5:   
        return Pronouns(pronouns[0], pronouns[1], pronouns[2], pronouns[3], pronouns[4])
    # With four, more than five, or fewer than free, this function needs to try again.
    else:
        print("Please enter either sub/obj/ref prononous or "
                "sub/obj/dep pos/indep pos/ref pronouns.")
        return get_custom_pronouns()

def fill_pronouns(text: str, pro: Pronouns):
    return text.format(sub=pro.subjective, obj=pro.objective,
            dep_pos=pro.dep_posessive, ind_pos=pro.indep_posessive,ref=pro.reflexive)

# This function gives the user a menu of common pronoun sets as well as an option to invoke
#   get_custom_pronouns() to enter a custom set.
def get_pronouns_menu():
    print("Select your preferred pronouns.")
    print("[1] They/them pronouns\n[2] He/him pronouns\n"
            "[3] She/her pronouns\n[c] Custom pronouns...")
    selection = input("Selection: ")
    results = {
            '1': Pronouns("they"),
            '2': Pronouns("he"),
            '3': Pronouns("she"),
            }
    if selection in results.keys():
        return results[selection]
    elif selection == 'c':
        return get_custom_pronouns()
    else:
        print("Please enter a valid selection.")
        return get_pronouns_menu()

pronouns = get_pronouns_menu()
print(fill_pronouns(
    "The player picks {ref} up off the ground. After adjusting {dep_pos} "
        "cap, {sub} looks about and grabs {dep_pos} dropped book, "
        "resolving to take it with {obj}.", pronouns))