.write not working in Python

I'm fairly new to Python so hopefully I'm just missing something obvious here, but it has me stumped. Snippet of my program below:

outFile = open('P4Output.txt', 'w')
outFile.write(output)
print output
print "Output saved to \"P4Output.txt\"\n"

output prints correctly to the console, but if I go open up the file it's blank. If I delete the file and execute my program again, the file is created but still is empty. I used this exact same block of code in another program of mine previously and it worked, and still works. However, if I open up Python and try something simple like:

f = open('test.txt', 'w')
f.write("test")

Again, test.txt is created but is left blank. What gives?