Buggy python submission (verdict: Time Limit Exceeded):
def main():  
  n, m = map(int, input().split())

  rootGroups = []

  for i in range(m):
    a, b = map(int, input().split())

    flag = False
    for j in range(len(rootGroups)):
      now = rootGroups[j]
      if a in now:
        now.append(b)
        flag = True
      if b in now:
        now.append(a)
        flag = True
    if not flag:
      rootGroups.append([a, b])

  for i in range(len(rootGroups)):
    rootGroups[i] = list(dict.fromkeys(rootGroups[i]))

  count = 0

  for v in rootGroups:
    count += len(v)


  print((len(rootGroups) - 1) + (n - count))

main()


Fixed submission:
import numpy as np

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())

def main():
  n, m = map(int, input().split())

  union = UnionFind(n)

  for _ in range(m):
    a, b = map(lambda x: int(x) - 1, input().split())
    union.union(a, b)

  print(union.group_count()-1)



main()

Buggy python submission (verdict: Time Limit Exceeded):
n, m = map(int, input().split())

rootGroups = []

for i in range(m):
  a, b = map(int, input().split())

  flag = False
  for j in range(len(rootGroups)):
    if a in rootGroups[j]:
      rootGroups[j].append(b)
      flag = True
    if b in rootGroups[j]:
      rootGroups[j].append(a)
      flag = True
  if not flag:
    rootGroups.append([a, b])

result = []

for i in range(len(rootGroups)):
  rootGroups[i] = list(dict.fromkeys(rootGroups[i]))

count = 0
for v in rootGroups:
  count += len(v)


print((len(rootGroups) - 1) + (n - count))



Fixed submission:
import numpy as np

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())

def main():
  n, m = map(int, input().split())

  union = UnionFind(n)

  for _ in range(m):
    a, b = map(lambda x: int(x) - 1, input().split())
    union.union(a, b)

  print(union.group_count()-1)



main()