Buggy python submission (verdict: Time Limit Exceeded):
import bisect
import sys
import math
input = sys.stdin.readline
import functools

from collections import defaultdict

############ ---- Input Functions ---- ############

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    s = input()
    return(list(s[:len(s) - 1]))
def invr():
    return(map(int,input().split()))

############ ---- Solution ---- ############

def diff(S, i, T):
    res = 0
    for j in range(len(T)):
        if S[i + j] != T[j]:
            res += 1
    return res

def solve():
    [N, M] = inlt()
    uf = [i for i in range(N)]
    rn = [1 for i in range(N)]

    def root(i):
        j = i
        while uf[j] != j:
            j = uf[j]
        uf[i] = j
        return j

    def union(i, j):
        if rn[i] > rn[j]:
            i, j = j, i
        ri = root(i)
        rj = root(j)
        if ri == rj:
            return
        uf[ri] = rj
        rn[rj] += rn[ri]

    for i in range(M):
        [a, b] = inlt()
        union(a - 1, b - 1)

    groups = defaultdict(int)
    res = 0
    for i in range(N):
        r = root(i)
        groups[r] += 1
        res = max(res, groups[r])
    
    return res

    

if len(sys.argv) > 1 and sys.argv[1].startswith("input"):
    f = open("./" + sys.argv[1], 'r')
    input = f.readline

res = solve()
print(str(res))


Fixed submission:
import bisect
import sys
import math
input = sys.stdin.readline
import functools

from collections import defaultdict

############ ---- Input Functions ---- ############

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    s = input()
    return(list(s[:len(s) - 1]))
def invr():
    return(map(int,input().split()))

############ ---- Solution ---- ############

def dfs(i, edges, visited):
    s = []
    if not visited[i]:
        s.append(i)
        visited[i] = True
    res = 0
    while len(s) > 0:
        v = s.pop()
        res += 1
        for i in edges[v]:
            if not visited[i]:
                s.append(i)
                visited[i] = True

    return res

def solve():
    [N, M] = inlt()
    edges = defaultdict(set)
    visited = [False for i in range(N)]

    for i in range(M):
        [a, b] = inlt()
        edges[a - 1].add(b - 1)
        edges[b - 1].add(a - 1)

    res = 0
    for i in range(N):
        res = max(res, dfs(i, edges, visited))
    
    return res

    

if len(sys.argv) > 1 and sys.argv[1].startswith("input"):
    f = open("./" + sys.argv[1], 'r')
    input = f.readline

res = solve()
print(str(res))

Buggy python submission (verdict: Time Limit Exceeded):
import bisect
import sys
import math
input = sys.stdin.readline
import functools

from collections import defaultdict

############ ---- Input Functions ---- ############

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    s = input()
    return(list(s[:len(s) - 1]))
def invr():
    return(map(int,input().split()))

############ ---- Solution ---- ############

def diff(S, i, T):
    res = 0
    for j in range(len(T)):
        if S[i + j] != T[j]:
            res += 1
    return res

def solve():
    [N, M] = inlt()
    uf = [i for i in range(N)]

    def root(i):
        j = i
        while uf[j] != j:
            j = uf[j]
        uf[i] = j
        return j

    def union(i, j):
        uf[root(i)] = root(j)

    for i in range(M):
        [a, b] = inlt()
        union(a - 1, b - 1)

    groups = defaultdict(int)
    res = 0
    for i in range(N):
        r = root(i)
        groups[r] += 1
        res = max(res, groups[r])
    
    return res

    

if len(sys.argv) > 1 and sys.argv[1].startswith("input"):
    f = open("./" + sys.argv[1], 'r')
    input = f.readline

res = solve()
print(str(res))


Fixed submission:
import bisect
import sys
import math
input = sys.stdin.readline
import functools

from collections import defaultdict

############ ---- Input Functions ---- ############

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    s = input()
    return(list(s[:len(s) - 1]))
def invr():
    return(map(int,input().split()))

############ ---- Solution ---- ############

def dfs(i, edges, visited):
    s = []
    if not visited[i]:
        s.append(i)
        visited[i] = True
    res = 0
    while len(s) > 0:
        v = s.pop()
        res += 1
        for i in edges[v]:
            if not visited[i]:
                s.append(i)
                visited[i] = True

    return res

def solve():
    [N, M] = inlt()
    edges = defaultdict(set)
    visited = [False for i in range(N)]

    for i in range(M):
        [a, b] = inlt()
        edges[a - 1].add(b - 1)
        edges[b - 1].add(a - 1)

    res = 0
    for i in range(N):
        res = max(res, dfs(i, edges, visited))
    
    return res

    

if len(sys.argv) > 1 and sys.argv[1].startswith("input"):
    f = open("./" + sys.argv[1], 'r')
    input = f.readline

res = solve()
print(str(res))

Buggy python submission (verdict: Runtime Error):
import bisect
import sys
import math
input = sys.stdin.readline
import functools

from collections import defaultdict

############ ---- Input Functions ---- ############

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    s = input()
    return(list(s[:len(s) - 1]))
def invr():
    return(map(int,input().split()))

############ ---- Solution ---- ############

def diff(S, i, T):
    res = 0
    for j in range(len(T)):
        if S[i + j] != T[j]:
            res += 1
    return res

def solve():
    [N, M] = inlt()
    uf = [i for i in range(N)]

    def root(i):
        if uf[i] == i:
            return i
        res = root(uf[i])
        uf[i] = res
        return res

    def union(i, j):
        uf[root(i)] = root(j)

    for i in range(M):
        [a, b] = inlt()
        union(a - 1, b - 1)

    groups = defaultdict(int)
    res = 0
    for i in range(N):
        r = root(i)
        groups[r] += 1
        res = max(res, groups[r])
    
    return res

    

if len(sys.argv) > 1 and sys.argv[1].startswith("input"):
    f = open("./" + sys.argv[1], 'r')
    input = f.readline

res = solve()
print(str(res))


Fixed submission:
import bisect
import sys
import math
input = sys.stdin.readline
import functools

from collections import defaultdict

############ ---- Input Functions ---- ############

def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    s = input()
    return(list(s[:len(s) - 1]))
def invr():
    return(map(int,input().split()))

############ ---- Solution ---- ############

def dfs(i, edges, visited):
    s = []
    if not visited[i]:
        s.append(i)
        visited[i] = True
    res = 0
    while len(s) > 0:
        v = s.pop()
        res += 1
        for i in edges[v]:
            if not visited[i]:
                s.append(i)
                visited[i] = True

    return res

def solve():
    [N, M] = inlt()
    edges = defaultdict(set)
    visited = [False for i in range(N)]

    for i in range(M):
        [a, b] = inlt()
        edges[a - 1].add(b - 1)
        edges[b - 1].add(a - 1)

    res = 0
    for i in range(N):
        res = max(res, dfs(i, edges, visited))
    
    return res

    

if len(sys.argv) > 1 and sys.argv[1].startswith("input"):
    f = open("./" + sys.argv[1], 'r')
    input = f.readline

res = solve()
print(str(res))