How to fix python error?

Question

Python

def gcd(a, b): 
    while b: 
        a, b = b, a % b 
    return a 

def main(a,b,c): 
    return(gcd(gcd(a,b),c))

def getPowers(n, p):
    vac=[]
    with open(str(p)+".txt", "r") as f:
        for x in range(1, n + 1):
            vac.append(f.readline(x))
    return vac

def detNumbers(n,p):
    xxx=0
    a1=[]
    a2=[]
    a3=[]
    vac=getPowers(n, p)
    for x in range(1, p):
        for y in range(x + 1, p-1):
            for z in range(y+1, p+1):
                if main(x,y,z)==1:
                    if gcd(x, y)==gcd(y, z)==gcd(x, z)==1:
                        if vac[x]+vac[y]==vac[z]:
                            xxx=xxx+1
                            a1[xxx].append(x)
                            a2[xxx].append(y)
                            a3[xxx].append(z)

    for c in range(1, p+1):
        with open("Тройки"+str(c)+".txt", "w") as f:
            for g in range(1, xxx + 1):
                f.write(a1[g] + " " + a2[g] + " " + a3[g] + "\n")

for pop in range(1, 1000+1):
    detNumbers(2000,pop)

Answer 1

Here are the errors

a1[xxx].append(x)
a2[xxx].append(y)
a3[xxx].append(z)

You are accessing list elements a1, a2 and a3, but initially the lists are empty and most likely you get an IndexError exception.
If you want to add an element to the list, then you need to write like this

a1.append(x)
a2.append(y)
a3.append(z)

Answer 2

Sorry, but there is no personal Python technical support here and no one will parse your code with terribly named variables. Learn to look for mistakes yourself, otherwise it will turn into a bad habit.
I can only recommend that you pay attention to the error in the Python emulator and google it. The emulator detects and shows errors well, so there should be no problems.

Answer 3

line 39, in detNumber(2000,1000)
line 29, in detNumber a1[xxx].append(x)