Buggy python submission (verdict: Time Limit Exceeded):
from heapq import *
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 unite(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 -size.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())
n=int(input())
X=[]
Y=[]
edge=[] 
for i in range(n):
  x,y=map(int,input().split())
  X.append((x,i))
  Y.append((y,i))
  edge.append((x,y))
X.sort()
Y.sort()
hq=[]
heapify(hq)
for i in range(n-1):
  x1,j1=X[i]
  x2,j2=X[i+1]
  y1,k1=Y[i]
  y2,k2=Y[i+1]
  heappush(hq,(x2-x1,j1,j2))
  heappush(hq,(y2-y1,k1,k2))
uf=UnionFind(n)
ans=0
while hq:
  w,s,t=heappop(hq)
  if uf.find(s)!=uf.find(t):
    uf.unite(s,t)
    ans+=w
print(ans)

Fixed submission:
from heapq import *
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 unite(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 -size.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())
n=int(input())
X=[]
Y=[]
edge=[] 
for i in range(n):
  x,y=map(int,input().split())
  X.append((x,i))
  Y.append((y,i))
  edge.append((x,y))
X.sort()
Y.sort()
hq=[]
heapify(hq)
for i in range(n-1):
  x1,j1=X[i]
  x2,j2=X[i+1]
  y1,k1=Y[i]
  y2,k2=Y[i+1]
  heappush(hq,(x2-x1,j1,j2))
  heappush(hq,(y2-y1,k1,k2))
uf=UnionFind(n)
ans=0
while hq:
  w,s,t=heappop(hq)
  if uf.find(s)!=uf.find(t):
    uf.unite(s,t)
    ans+=w
print(ans)

Buggy python submission (verdict: Runtime Error):
from heapq import *
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 unite(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 -size.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())
n=int(input())
X=[[] for i in range(n)]
Y=[[] for i in range(n)]
edge=[[] for i in range(n)] 
for i in range(n):
  x,y=map(int,input().split())
  X.append((x,i))
  Y.append((y,i))
  edge.append((x,y))
X.sort()
Y.sort()
hq=[]
heapify(hq)
for i in range(n-1):
  x1,j1=X[i]
  x2,j2=X[i+1]
  y1,k1=Y[i]
  y2,k2=Y[i+1]
  heappush(hq,(x2-x1,j1,j2))
  heappush(hq,(y2-y1,k1,k2))
uf=UnionFind(n)
ans=0
while hq:
  w,s,t=heappop(hq)
  if uf.find(s)!=uf.find(t):
    uf.unite(s,t)
    ans+=w
print(ans)

Fixed submission:
from heapq import *
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 unite(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 -size.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())
n=int(input())
X=[]
Y=[]
edge=[] 
for i in range(n):
  x,y=map(int,input().split())
  X.append((x,i))
  Y.append((y,i))
  edge.append((x,y))
X.sort()
Y.sort()
hq=[]
heapify(hq)
for i in range(n-1):
  x1,j1=X[i]
  x2,j2=X[i+1]
  y1,k1=Y[i]
  y2,k2=Y[i+1]
  heappush(hq,(x2-x1,j1,j2))
  heappush(hq,(y2-y1,k1,k2))
uf=UnionFind(n)
ans=0
while hq:
  w,s,t=heappop(hq)
  if uf.find(s)!=uf.find(t):
    uf.unite(s,t)
    ans+=w
print(ans)