My edited version of G_heinz' damage calc

import math
import os
#import os and therefore the last command I added are windows-only ~M

#first gather information about the attacking and defending pokemon

L = input("Attacking Pokemon's level: ")
A = input("Attacking Pokemon's offensive stat value: ")
P = input("Attacking move's base power: ")
D = input("Defending Pokemon's defensive stat value: ")
HP = input("Defending Pokemon's HP value: ")
xitem = input("Attack stage after boosts/drops: ")
defstage = input("Defense stage after boosts/drops: ")

badgeboost = raw_input("Does a badge boost apply? y or n: ")
softwater = raw_input("Does a mystic water or soft sand boost apply? y or n: ")
torrentcheck = raw_input("Does Torrent apply? y or n: ")
doublecheck = raw_input("Does the attack target both defending Pokemon? y or n: ")
stabcheck = raw_input("Is the move STAB? y or n: ")
raincheck = raw_input("Is the move boosted by weather? y or n: ")
suncheck = raw_input("Is the move negatively affected by weather? y or n: ")
typeeffect = input("What is the type-effectiveness? 0.25, 0.5, 1, 2, or 4: ")
lsrefcheck = raw_input("Is light screen or reflect active? y or n: ")

#next modify the attack stat based on the answers to the above

if badgeboost == "y":
    A = int(A*1.1)
elif badgeboost == "n":
    A = A

if softwater == "y":
    A = int(A*1.1)
elif softwater == "n":
    A = A
if xitem == -1:
    A = int(A*10/15)
elif xitem == 0:
    A = A
elif xitem == 1:
    A = int(A*15/10)
elif xitem == 2:
    A = int(A*20/10)
elif xitem == 3:
    A = int(A*25/10)
elif xitem == 4:
    A = int(A*30/10)
elif xitem == 5:
    A = int(A*35/10)
elif xitem == 6:
    A = int(A*40/10)

if defstage == -1:
    D = int(D*10/15)
elif defstage == 0:
    D = D
elif defstage == 1:
    D = int(D*15/10)
elif defstage == 2:
    D = int(D*20/10)
elif defstage == 3:
    D = int(D*25/10)
elif defstage == 4:
    D = int(D*30/10)
elif defstage == 5:
    D = int(D*35/10)
elif defstage == 6:
    D = int(D*40/10)

if torrentcheck == "y":
    P = int(P*1.5)
elif torrentcheck == "n":
    P = P

#third calculate the base damage of the attack before a few additional modifiers

basedamage = int(int(int(2*L/5+2)*A*P/D)/50)

#then include the relevant modifiers

if lsrefcheck == "y" and doublecheck == "n":
    basedamage = int(basedamage/2)
elif lsrefcheck == "y" and doublecheck == "y":
    basedamage = int((basedamage*2)/3)
elif lsrefcheck == "n" and doublecheck == "n":
    basedamage = basedamage

#I renamed weathercheck to raincheck ~M
if raincheck == "y":
    basedamage = int(basedamage*1.5)
elif raincheck == "n":
    basedamage = basedamage

#and added suncheck ~M
if suncheck == "y":
    basedamage = int(basedamage*0.5)
elif suncheck == "n":
    basedamage = basedamage

if doublecheck == "y":
    basedamage = int(basedamage/2)
elif doublecheck == "n":
    basedamage = basedamage

basedamage += 2

#factor in STAB

if stabcheck == "y":
    basedamage = int(basedamage*1.5)
elif stabcheck == "n":
    basedamage = basedamage

#then type-effectiveness

damage = basedamage * typeeffect

#finally factor in damage variance and print

R = range(85,101)
missedrange = 0
for i in R:
    roll = int((damage*i)/100)
    if HP - roll > 0:
        missedrange += 1

OHKO = 100 * ((16 - missedrange)/float(16))
minroll = int((damage*85)/100)
#Calculating damage in % ~M
percminroll = float(float(minroll) / float(HP) * 100)
percdamage = float(float(damage) / float(HP) * 100)

print("{}-{} damage".format(str(minroll), str(damage)))
print("{}%-{}% damage".format(str(percminroll), str(percdamage)))
print("{}% chance to OHKO".format(OHKO))

#I added a Pause here, because the script would autoexit for me ~M
os.system("pause")