Random Password with at least one uppercase,one lowercase,one digit and one special char

import random
import string
all_letters = string.ascii_letters
all_uppercase = string.ascii_uppercase
all_lowercase = string.ascii_lowercase
all_numbers = string.digits
all_special = string.punctuation
all = all_letters+all_numbers+all_special

n = int(input("How many characters in your password?   "))

#ensuring all requirements are fullfilled first
password = " "
password += random.choice(all_lowercase)
password += random.choice(all_uppercase)
password += random.choice(all_numbers)
password += random.choice(all_special)

#filling the remaining characters by substracting 4 from n
for char in range(0,n-4):
    char = random.choice(all)

    password = password + char


print("your random password is :", password)