Calculating the percentage on Python 2.7 An attack with magnitude M will be successful with a chance of (100-M)%. That is, higher magnitude means higher risk of missing it. For instance, if M is 30, the chance of succeeding would be 70%, whereas, if M is 10, the chance of succeeding would be 90%. If an attack with magnitude M is successful, the attacked hero's health points will decrease by M. If the user writes more than
50 or less than 1, the game should warn the player, and re-ask for another attack magnitude as below.

import random

# ---

char1 = raw_input("Player One: ")

while char1 == "":
    char1 = raw_input("Please enter your name: ")

char2 = raw_input("Player two: ")
while char2 == char1:
    char2 = raw_input(char1 + " name is taken, please choose another name: ")
while char2 == "":
    char2 = raw_input("Please enter your name: ")
print char1, "and", char2, "welcome to the game."

# ---

health1 = 50
health2 = 50

print char1, '|' * health1
print char2, '|' * health2

toss = random.randint(0, 1)

if toss == 0:
    print char1, "will start the game"
else:
    print char2, "will start the game"

# ---

while health1 &gt; 0 and health2 &gt; 0:
    if toss == 0:
        n = input(char1 + " select n force: ")
        health2 -= n
        print char2, '|' * health2 + char1,'|' * health1
        toss = 1 # change player
    else:
        n = input(char2 + " select n force: ")
        health1 -= n
        print char1, '|' * health1 + char2,'|' * health2
        toss = 0 # change player

# ---

if health1 &gt; 0:
    print char2, 'wins'
else:
    print char1, 'wins'
I take it from your code the game works like this:


Each player enters their names. The names can't be blank nor the same with each other.
A coin is tossed to determine the turn order.
The turn player decides the amount of damage (M) he wants to deal against the other player. The chance of dealing damage is calculated by (100 - M).


With that, I have this code:

player1, player2 = input_player_names()
print("Welcome to the game {} and {}".format(player1, player2))
print("Tossing coin... Heads for {}; tails for {}".format(player1, player2))
turn_order = determine_turn_order([player1, player2])
print(turn_order[0], "plays first")
play(turn_order)


And the respective implementations:

def input_player_names():
    player1 = ""
    player2 = ""
    while player1 == "":
        player1 = input("Player 1, please enter your name.")
    while player2 == "" or player2 == player1:
        player2 = input("Player 2, please enter your name.")
    return player1, player2

def determine_turn_order(player_list):
    turn_order = []
    toss = random.randint(0, 1)
    turn_order.append(player_list[toss])
    turn_order.append(player_list[toss + 1 % 2])
    return turn_order

def play(turn_order):
    player_health_points_list = [50, 50]
    turn_number = 0
    while there_are_no_winners_yet(player_health_points_list):
        turn_player = turn_order[turn_number % 2]
        player_is_sure = False
        chance = 100
        damage_to_deal = 0
        while not player_is_sure:
            damage_to_deal = input(turn_player + " enter damage you want to deal: ")
            damage_to_deal = int(damage_to_deal)
            chance = chance - damage_to_deal
            if chance &lt; 50:
                player_is_sure = bool(input("You have only a {}% chance of dealing damage. Are you sure you want to push through? Input 1 for yes; 0  for no.".format(chance)))
            else:
                player_is_sure = True

        # Here's how I'd calculate determine whether the attack hits or not
        if chance &gt; random.randint(1, 100):
            player_health_points_list[(turn_number + 1) % 2] -= damage_to_deal
        turn_number = turn_number + 1
        print(turn_order[0], '|' * player_health_points_list[0])
        print(turn_order[1], '|' * player_health_points_list[1])
    declare_winner(turn_order, player_health_points_list)

def there_are_no_winners_yet(player_health_points_list):
    return player_health_points_list[0] &gt; 0 and player_health_points_list[1] &gt; 0

def declare_winner(turn_order, player_health_points_list):
    print("The winner is {}".format(turn_order[0] if player_health_points_list[0] &gt; player_health_points_list[1] else turn_order[1]))