Writing output to file not working: No errors found

Question

I am trying to write an output a result in a file in Python but it is not working neither it is showing any error.

Following is my code:

from collections import namedtuple
from pprint import pprint as pp

final_data = []
inf = float('inf')
Edge = namedtuple('Edge', 'start, end, cost')
class Graph():
def __init__(self, edges):
    self.edges = edges2 = [Edge(*edge) for edge in edges]
    self.vertices = set(sum(([e.start, e.end] for e in edges2), []))

def dijkstra(self, source, dest):
    assert source in self.vertices
    dist = {vertex: inf for vertex in self.vertices}
    previous = {vertex: None for vertex in self.vertices}
    dist[source] = 0
    q = self.vertices.copy()
    neighbours = {vertex: set() for vertex in self.vertices}
    for start, end, cost in self.edges:
        neighbours[start].add((end, cost))
    #pp(neighbours)

    while q:
        u = min(q, key=lambda vertex: dist[vertex])
        q.remove(u)
        if dist[u] == inf or u == dest:
            break
        for v, cost in neighbours[u]:
            alt = dist[u] + cost
            if alt < dist[v]:                                  
                dist[v] = alt
                previous[v] = u
    #pp(previous)
    s, u = [], dest
    while previous[u]:
        s.insert(0, u)
        u = previous[u]
    s.insert(0, u)
    return s

start_point = input('Enter the starting point: ') 
end_point = input('Enter the ending point: ')
file_name = input('Enter the input file name: ')
output_file = input('Enter the output file name: ')
f = open(file_name, 'r')

data = f.readlines()

for line in data:
    f_line = line
    values = f_line.split()
    values[2] = int(values[2])
    final_data.append(values)

graph = Graph(final_data)




f = open(output_file, 'a')

result = str(pp(graph.dijkstra(start_point, end_point)))
f.write(result)

Note: Ignore indentations

I am not sure where exactly i am making the mistake. I tried writing to the file using append(a) and write(w) but both did not work. All the paths to the files are correct and input file is reading perfectly and output file is also in the same folder.

Thanks for the help but now its writing None rather then the exact answer — Osama Yawar
– Osama Yawar, Commented Jan 25, 2014 at 22:21

zmo · Accepted Answer · 2014-01-25 22:27:35Z

1

f = open(output_file, 'a')
result = str(pp(graph.dijkstra(start_point, end_point)))
f.write(result)

you want instead:

with open(output_file, 'a') as f:
    result = pprint.pformat(graph.dijkstra(start_point, end_point))
    f.write(result)

because pprint.pprint() is a replacement of print and thus has the same "prototype" which returns nothing. pprint.pformat has been made so you can "print" to a string. Though, you may want to do

with open(output_file, 'a') as f:
    pp(graph.dijkstra(start_point, end_point), stream=f)

as the help of pprint states:

Help on function pprint in module pprint:

pprint(object, stream=None, indent=1, width=80, depth=None)
    Pretty-print a Python object to a stream [default is sys.stdout].

answered Jan 25, 2014 at 22:27

zmo

24.9k4 gold badges58 silver badges91 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Writing output to file not working: No errors found

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related