如何根据用户输入执行不同的打印功能

您可以创建函数。我在这里命名了它，它打印 if is passed 和 print
if is passed：messagewelcomeTruetoo bad thenFalse

# Use int while you ask for an integer
age = int(input("enter your age: "))

def message(msg):
    if msg is True:
        print("welcome")
    elif msg is False:
        print("too bad then")

if age == 18: #It's probably "age >= 18" that you need
    message(True)
else: 
    enter = input("you're not old enough, would you like to enter anyways?: ")
    if enter.strip().lower() in ["yes","y"]:
        message(True)
    elif enter.strip().lower() in ["n","no"]:
        message(False)
    else:
        print("Invalid input exiting...")

请注意，当使用 时，只要第一个表达式（按指定的顺序）是 ，下一个表达式就会被忽略，因为结果将无关紧要。使用时也会发生同样的情况;一旦找到 A，下一个表达式就会被忽略，因为结果将是orTrueTrueandFalseFalse

对于您的具体问题，解决方案是：

if int(input("enter your age: ")) >= 18 or input("you're not old enough, would you like to enter anyways? ").lower().startswith('y'):
    print("welcome")  
else: 
    print("too bad then")

对于更通用的任务（编写解释器或类似任务），您需要使用函数指针和查找表（通常是字典）。 下面是一个工作示例：

import math
import time

def add(*args):
    "Adds numbers together"
    if len(args)>0:
        print(sum((float(arg) for arg in args)))

def mult(*args):
    "Multiplies numbers together"
    if len(args)>0:
        print(math.prod((float(arg) for arg in args)))
        
def nothing(*args):
    pass
        
def alias(*args):
    "Creates a new alias for a given action"
    action, alias, *_ = args
    if action not in LUT:
        print("Cannot create an alias for an undefined action!")
    else:
        aliases[alias]=action
        print(f"Successfully created alias '{alias}' for '{action}'")
    
def print_help(*args):
    "Displays valid options and what they do"
    for keyword in LUT:
        doc = LUT[keyword].__doc__
        print(f"{keyword} : {doc if doc is not None else '?'}")
    print(f"To exit the program, type any one of: {', '.join(termination_keywords)}")
    
def print_aliases(*args):
    groupings= {action : [] for action in LUT}
    for alias in aliases:
        groupings[aliases[alias]].append(alias)
    for action, aliases_ in groupings.items():
        if len(aliases_)>0:
            print(f"{action} : {', '.join(aliases_)}")
    
# Look Up Table
LUT = {
    'help':print_help,
    'add':add,
    'mult':mult,
    'nop' : nothing,
    'alias' : alias,
    'print_aliases': print_aliases
    }

aliases = {
    '+':'add',
    'sum':'add',
    'total': 'add',
    '*':'mult',
    'multiply':'mult',
    'prod':'mult',
    'nothing' : 'nop',
    'pass': 'nop'
}
    
termination_keywords = {'end','exit','quit','q'}

print(f"""Enter your the desired action and its arguments as space seperated values.
For example: add 1 2 3 4 5

Defined actions are:""")
print_help()
# Sometimes the input is displayed before the help is done printing, a small delay fixes the issue
time.sleep(0.5)

while True:
    print("#"*20)
    action, *args = input("What do you want to do? ").split(' ')
    action = action.lower()
    if action in termination_keywords:
        break;
    if action in LUT:
        LUT[action](*args)
    elif action in aliases:
        LUT[aliases[action]](*args)
    else:
        print("Undefined action!")