In the above solution, repeated here:
f = open('file.txt', 'r')
try:
# do stuff with f
finally:
f.close()
if something bad happens (you never know ...) after opening the file successfully and before the try, the file will not be closed, so a safer solution is:
f = None
try:
f = open('file.txt', 'r')
# do stuff with f
finally:
if f is not None:
f.close()