Password security level check

Xiaoming works in the card center, and many system accounts used require a security password. A password can be called a secure password if it meets the following specifications:
1. The password contains at least 6 characters and at most 20 characters;
2. It contains at least one lowercase letter, at least one uppercase letter, and at least one number;

3. There cannot be 3 consecutive identical letters.

Please write a function that checks if a password is a secure password.

The input is a string as the password, and the output is the minimum number of changes to make this password secure. Returns 0 if it is already a secure password.

Note: Inserting, deleting, or replacing a character is regarded as a change.

Just finished the code for the first step: check if the password is secure

s=input("please input your passwords:")

flag_upper=flag_little=flag_num=others=0

if len(s)<6 or len(s)>20:
    print("passwords is too short！")

else:
    for j in range(len(s)-3):
        if type(s[j])==type(s[j+1]) and type(s[j])==type(s[i+2]):
            if s[j]==s[j+1] and s[j]==s[j+2]:
                print("can't use the same three word")
            else:
                pass
        else:
            pass
             
    for i in s:
        if ord(i)>=97 and ord(i)<=122:
            flag_little+=1
        elif ord(i)>=65 and ord(i)<=90:
            flag_upper+=1
        elif ord(i)>=48 and ord(i)<=57:
            flag_num+=1
        else:
            others+=1
    if flag_upper>0 and flag_little>0 and flag_num>0:
        print("successful")
    else:
        print("passwords is invalid")