如果输入一无所有或负数python认为它是一个字符串

Question

如果您需要，这是我的完整代码： （打印内容是德语），

import random
import time

n = 0
guess = 0
tries = 0

print("###Zahlen erraten###")
time.sleep(2)
print("")
time.sleep(1)


while True:
    n = input("Grenze eingeben: ")
    if n.isdigit():
        break

n = int(n)

Number = random.randint(0,n)
print(Number)
print(type(Number))

while True:
    guess = input("Zahl erraten: ")
    if guess.isdigit():
        guess = int(guess)
        print(type(guess))
        while guess == None or guess < 0:
            guess = input("Neue eingabe: ")
            if guess.isdigit():
                guess = int(guess)
                print(type(guess))


    if guess == Number:
        tries += 1
        break
    elif guess < Number:
        print("Die gesuchte Zahl ist größer!")
        tries += 1
        pass
    elif guess > Number:
        print("Die gesuchte Zahl ist kleiner")
        tries += 1
        pass


print("Gut gemacht! Die gesuchte Zahl ist "+ str(Number) + ". ")
print("Anzahl an versuchen: "+str(tries))

这是错误消息，如果我输入负数，或者在变量“猜测”中没有任何内容，

Traceback (most recent call last):
  File "C:\Users\micha\PycharmProjects\NumberGuesser\NumberGuesser.py", line 40, in <module>
    elif guess < Number:
TypeError: '<' not supported between instances of 'str' and 'int'

则该问题在第40行中，Elif Guess＆lt;数字：如果有人可以帮助我解决这个问题，我会很感激。