Buggy python submission (verdict: Time Limit Exceeded):
n=int(input())
xy=[list(map(int,input().split())) for _ in range(n)]
x,y=zip(*xy)
x=list(zip(list(range(n)),x))
y=list(zip(list(range(n)),y))
x.sort(key=lambda a:a[1])
y.sort(key=lambda a:a[1])
d=[]
for i in range(n-1):
  d.append([x[i+1][1]-x[i][1],1,x[i+1][0],x[i][0]])
  d.append([y[i+1][1]-y[i][1],1,y[i+1][0],y[i][0]])
d.sort(key=lambda a:a[0],reverse=True)
# Union FInd
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.parents[x] > self.parents[y]:
            x, y = y, x
        self.parents[x] += self.parents[y]
        self.parents[y] = x
    def size(self, x):
        return -self.parents[self.find(x)]
    def same(self, x, y):
        return self.find(x) == self.find(y)
    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]
    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]
    def group_count(self):
        return len(self.roots())
    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}
    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

ans=0
flg=True
uf=UnionFind(n)
while d and uf.group_count()>1:
  dist,f,i,j=d.pop()
  if uf.same(i,j):
    continue
  uf.union(i,j)
  ans+=dist
print(ans)

Fixed submission:
n=int(input())
xy=[list(map(int,input().split())) for _ in range(n)]
x,y=zip(*xy)
x=list(zip(range(n),x))
y=list(zip(range(n),y))
x.sort(key=lambda a:a[1])
y.sort(key=lambda a:a[1])
d=[]
for i in range(n-1):
  d.append([x[i+1][1]-x[i][1],x[i+1][0],x[i][0]])
  d.append([y[i+1][1]-y[i][1],y[i+1][0],y[i][0]])
d.sort(key=lambda a:a[0],reverse=True)
# Union FInd
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.parents[x] > self.parents[y]:
            x, y = y, x
        self.parents[x] += self.parents[y]
        self.parents[y] = x
    def size(self, x):
        return -self.parents[self.find(x)]
    def same(self, x, y):
        return self.find(x) == self.find(y)
    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]
    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]
    def group_count(self):
        return len(self.roots())
    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}
    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

ans=0
uf=UnionFind(n)
while d:
  dist,i,j=d.pop()
  if uf.same(i,j):
    continue
  uf.union(i,j)
  ans+=dist
print(ans)