Problem p02782 (python)

Fixed submission:
MOD=10**9+7
class ModInt:
    def __init__(self, x):
        self.x = x % MOD

    def __str__(self):
        return str(self.x)

    __repr__ = __str__

    def __add__(self, other):
        return (
            ModInt(self.x + other.x) if isinstance(other, ModInt) else
            ModInt(self.x + other)
        )

    def __sub__(self, other):
        return (
            ModInt(self.x - other.x) if isinstance(other, ModInt) else
            ModInt(self.x - other)
        )

    def __mul__(self, other):
        return (
            ModInt(self.x * other.x) if isinstance(other, ModInt) else
            ModInt(self.x * other)
        )

    def __truediv__(self, other):
        return (
            ModInt(
                self.x * pow(other.x, MOD - 2, MOD)
            ) if isinstance(other, ModInt) else
            ModInt(self.x * pow(other, MOD - 2, MOD))
        )

    def __pow__(self, other):
        return (
            ModInt(pow(self.x, other.x, MOD)) if isinstance(other, ModInt) else
            ModInt(pow(self.x, other, MOD))
        )

    __radd__ = __add__

    def __rsub__(self, other):
        return (
            ModInt(other.x - self.x) if isinstance(other, ModInt) else
            ModInt(other - self.x)
        )

    __rmul__ = __mul__

    def __rtruediv__(self, other):
        return (
            ModInt(
                other.x * pow(self.x, MOD - 2, MOD)
            ) if isinstance(other, ModInt) else
            ModInt(other * pow(self.x, MOD - 2, MOD))
        )

    def __rpow__(self, other):
        return (
            ModInt(pow(other.x, self.x, MOD)) if isinstance(other, ModInt) else
            ModInt(pow(other, self.x, MOD))
        )
r1,c1,r2,c2=map(int,input().split())
l=[1]*2000022
for i in range(1,2000022):
  l[i]=l[i-1]*ModInt(i)
def comb(a,b):
  c,d=int(a),int(b)
  if a==b or b==0 or a==0:return 1
  return l[c]/l[d]/l[c-d]
ans=((ModInt(r2)+2)*comb(c2+r2+2,r2+2)-ModInt(c2)-1)/(ModInt(c2)+1)-((ModInt(r1)+1)*comb(c2+r1+1,r1+1)-ModInt(c2)-1)/(ModInt(c2)+1)-((ModInt(r2)+2)*comb(c1+r2+1,r2+2)-ModInt(c1)-2)/ModInt(c1)+((ModInt(r1)+1)*comb(c1+r1,r1+1)-ModInt(c1)-2)/ModInt(c1)
print(ans)

Buggy submission (verdict: Runtime Error):
MOD=10**9+7
class ModInt:
    def __init__(self, x):
        self.x = x % MOD

    def __str__(self):
        return str(self.x)

    __repr__ = __str__

    def __add__(self, other):
        return (
            ModInt(self.x + other.x) if isinstance(other, ModInt) else
            ModInt(self.x + other)
        )

    def __sub__(self, other):
        return (
            ModInt(self.x - other.x) if isinstance(other, ModInt) else
            ModInt(self.x - other)
        )

    def __mul__(self, other):
        return (
            ModInt(self.x * other.x) if isinstance(other, ModInt) else
            ModInt(self.x * other)
        )

    def __truediv__(self, other):
        return (
            ModInt(
                self.x * pow(other.x, MOD - 2, MOD)
            ) if isinstance(other, ModInt) else
            ModInt(self.x * pow(other, MOD - 2, MOD))
        )

    def __pow__(self, other):
        return (
            ModInt(pow(self.x, other.x, MOD)) if isinstance(other, ModInt) else
            ModInt(pow(self.x, other, MOD))
        )

    __radd__ = __add__

    def __rsub__(self, other):
        return (
            ModInt(other.x - self.x) if isinstance(other, ModInt) else
            ModInt(other - self.x)
        )

    __rmul__ = __mul__

    def __rtruediv__(self, other):
        return (
            ModInt(
                other.x * pow(self.x, MOD - 2, MOD)
            ) if isinstance(other, ModInt) else
            ModInt(other * pow(self.x, MOD - 2, MOD))
        )

    def __rpow__(self, other):
        return (
            ModInt(pow(other.x, self.x, MOD)) if isinstance(other, ModInt) else
            ModInt(pow(other, self.x, MOD))
        )
r1,c1,r2,c2=map(int,input().split())
l=[1]*2000002
for i in range(1,2000002):
  l[i]=l[i-1]*ModInt(i)
def comb(a,b):
  c,d=int(a),int(b)
  if a==b or b==0 or a==0:return 1
  return l[c]/l[d]/l[c-d]
ans=((ModInt(r2)+2)*comb(c2+r2+2,r2+2)-ModInt(c2)-1)/(ModInt(c2)+1)-((ModInt(r1)+1)*comb(c2+r1+1,r1+1)-ModInt(c2)-1)/(ModInt(c2)+1)-((ModInt(r2)+2)*comb(c1+r2+1,r2+2)-ModInt(c1)-2)/ModInt(c1)+((ModInt(r1)+1)*comb(c1+r1,r1+1)-ModInt(c1)-2)/ModInt(c1)
print(ans)