Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque
import copy
import heapq

from math import *

def get_read_func(fileobject):
    if fileobject == None :
        return raw_input
    else:
        return fileobject.readline


def main():
    if len(sys.argv) > 1:
        f = open(sys.argv[1])
    else:
        f = None
    read_func = get_read_func(f);
    input_raw = read_func().strip().split()
    [N, M] =  [int(input_raw[0]), int(input_raw[1])]
    graph = {}
    for i in range(M):
        input_raw = read_func().strip().split()
        [a, b, c] =  [int(input_raw[0]), int(input_raw[1]), -long(input_raw[2])]
        if a not in graph:
            graph[a] = [(b, c)]
        else:
            graph[a].append((b, c))

    #dummy_inf = long(sys.maxint) * long(sys.maxint)
    dist_list =[long(sys.maxint) * long(sys.maxint) for i in range(N + 1)]
    dist_list[1] = 0L

    for i in range(0, 2 * N):
        for j in range(1, N + 1):
            if j not in graph:
                continue
            for edge in graph[j]:
                if dist_list[j] < long(sys.maxint) * long(sys.maxint):
                    new_cost = dist_list[j] + edge[1]
                    if new_cost < dist_list[edge[0]]:
                        dist_list[edge[0]] = new_cost
                        if (i >= N - 1 and edge[0] == N):
                            print "inf"
                            return
    print -dist_list[N]


if __name__ == '__main__':
    main()

Fixed submission:
import sys
from collections import deque
import copy
import heapq

from math import *

def get_read_func(fileobject):
    if fileobject == None :
        return raw_input
    else:
        return fileobject.readline


def main():
    if len(sys.argv) > 1:
        f = open(sys.argv[1])
    else:
        f = None
    read_func = get_read_func(f);
    input_raw = read_func().strip().split()
    [N, M] =  [int(input_raw[0]), int(input_raw[1])]
    graph = {}
    for i in range(M):
        input_raw = read_func().strip().split()
        [a, b, c] =  [int(input_raw[0]), int(input_raw[1]), -long(input_raw[2])]
        if a not in graph:
            graph[a] = [(b, c)]
        else:
            graph[a].append((b, c))

    dummy_inf = long(sys.maxint) * long(sys.maxint)
    dist_list =[dummy_inf for i in range(N + 1)]
    dist_list[1] = 0L

    for i in range(0, 2 * N):
        for j in range(1, N + 1):
            if j not in graph:
                continue
            for edge in graph[j]:
                if dist_list[j] < dummy_inf:
                    new_cost = dist_list[j] + edge[1]
                    if new_cost < dist_list[edge[0]]:
                        dist_list[edge[0]] = new_cost
                        if (i >= N - 1 and edge[0] == N):
                            print "inf"
                            return
    print -dist_list[N]


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque
import copy
import heapq

from math import *

def get_read_func(fileobject):
    if fileobject == None :
        return raw_input
    else:
        return fileobject.readline


def main():
    if len(sys.argv) > 1:
        f = open(sys.argv[1])
    else:
        f = None
    read_func = get_read_func(f);
    input_raw = read_func().strip().split()
    [N, M] =  [int(input_raw[0]), int(input_raw[1])]
    graph = {}
    for i in range(M):
        input_raw = read_func().strip().split()
        [a, b, c] =  [int(input_raw[0]), int(input_raw[1]), int(input_raw[2])]
        if a not in graph:
            graph[a] = [(b, -long(c))]
        else:
            graph[a].append((b, -long(c)))

    dist_list =[long(sys.maxint) * long(sys.maxint) for i in range(N + 1)]
    dist_list[1] = 0L
    for i in range(0, 2 * N):
        for j in range(1, N + 1):
            if j not in graph:
                continue
            for edge in graph[j]:
                if dist_list[j] < long(sys.maxint) * long(sys.maxint):
                    if dist_list[j] + edge[1] < dist_list[edge[0]]:
                        dist_list[edge[0]] = dist_list[j] + edge[1]
                        if (i >= N - 1 and edge[0] == N):
                            print "inf"
                            return
    print -dist_list[N]


if __name__ == '__main__':
    main()


Fixed submission:
import sys
from collections import deque
import copy
import heapq

from math import *

def get_read_func(fileobject):
    if fileobject == None :
        return raw_input
    else:
        return fileobject.readline


def main():
    if len(sys.argv) > 1:
        f = open(sys.argv[1])
    else:
        f = None
    read_func = get_read_func(f);
    input_raw = read_func().strip().split()
    [N, M] =  [int(input_raw[0]), int(input_raw[1])]
    graph = {}
    for i in range(M):
        input_raw = read_func().strip().split()
        [a, b, c] =  [int(input_raw[0]), int(input_raw[1]), -long(input_raw[2])]
        if a not in graph:
            graph[a] = [(b, c)]
        else:
            graph[a].append((b, c))

    dummy_inf = long(sys.maxint) * long(sys.maxint)
    dist_list =[dummy_inf for i in range(N + 1)]
    dist_list[1] = 0L

    for i in range(0, 2 * N):
        for j in range(1, N + 1):
            if j not in graph:
                continue
            for edge in graph[j]:
                if dist_list[j] < dummy_inf:
                    new_cost = dist_list[j] + edge[1]
                    if new_cost < dist_list[edge[0]]:
                        dist_list[edge[0]] = new_cost
                        if (i >= N - 1 and edge[0] == N):
                            print "inf"
                            return
    print -dist_list[N]


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque
import copy
import heapq

from math import *

def get_read_func(fileobject):
    if fileobject == None :
        return raw_input
    else:
        return fileobject.readline


def main():
    if len(sys.argv) > 1:
        f = open(sys.argv[1])
    else:
        f = None
    read_func = get_read_func(f);
    input_raw = read_func().strip().split()
    [N, M] =  [int(input_raw[0]), int(input_raw[1])]
    graph = {}
    for i in range(M):
        input_raw = read_func().strip().split()
        [a, b, c] =  [int(input_raw[0]), int(input_raw[1]), int(input_raw[2])]
        if a not in graph:
            graph[a] = [(b, -long(c))]
        else:
            graph[a].append((b, -long(c)))

    dist_list =[long(sys.maxint) * long(sys.maxint) for i in range(N + 1)]
    dist_list[1] = 0L
    for i in range(0, 2 * N):
        for j in range(1, N + 1):
            if j not in graph:
                continue
            for edge in graph[j]:
                if dist_list[j] < long(sys.maxint) * long(sys.maxint):
                    if dist_list[j] + edge[1] < dist_list[edge[0]]:
                        dist_list[edge[0]] = dist_list[j] + edge[1]
                        if (i >= N - 1 and edge[0] == N):
                            print "inf"
                            return
    print -dist_list[N]


if __name__ == '__main__':
    main()


Fixed submission:
import sys
from collections import deque
import copy
import heapq

from math import *

def get_read_func(fileobject):
    if fileobject == None :
        return raw_input
    else:
        return fileobject.readline


def main():
    if len(sys.argv) > 1:
        f = open(sys.argv[1])
    else:
        f = None
    read_func = get_read_func(f);
    input_raw = read_func().strip().split()
    [N, M] =  [int(input_raw[0]), int(input_raw[1])]
    graph = {}
    for i in range(M):
        input_raw = read_func().strip().split()
        [a, b, c] =  [int(input_raw[0]), int(input_raw[1]), -long(input_raw[2])]
        if a not in graph:
            graph[a] = [(b, c)]
        else:
            graph[a].append((b, c))

    dummy_inf = long(sys.maxint) * long(sys.maxint)
    dist_list =[dummy_inf for i in range(N + 1)]
    dist_list[1] = 0L

    for i in range(0, 2 * N):
        for j in range(1, N + 1):
            if j not in graph:
                continue
            for edge in graph[j]:
                if dist_list[j] < dummy_inf:
                    new_cost = dist_list[j] + edge[1]
                    if new_cost < dist_list[edge[0]]:
                        dist_list[edge[0]] = new_cost
                        if (i >= N - 1 and edge[0] == N):
                            print "inf"
                            return
    print -dist_list[N]


if __name__ == '__main__':
    main()