Why the following python code does not print to file

Question

from sys import stdout
stdout = open('file', 'w')
print 'test'
stdout.close()

does create the file, but it contains nothing.

I had to use

import sys
sys.stdout = open('file', 'w')
print 'test'
sys.stdout.close()

But wouldn't the from ... import... automatically make the name available? Why do I still have to use sys.stdout instead of stdout?

Answer 1

The problem is this: print is equivalent to sys.stdout.write().

So when you do from sys import stdout, the variable stdout won't be used by print.

But when you do

import sys
print 'test'

it actually writes to sys.stdout which is pointing to the file you opened.

Analysis

from sys import stdout
stdout = open('file', 'w')
print 'test' # calls sys.stdout.write('test'), which print to the terminal
stdout.close()

---

import sys
sys.stdout = open('file', 'w')
print 'test' # calls sys.stdout.write('test'), which print to the file
sys.stdout.close()

Conclusion

This works...

from sys import stdout
stdout = open('file', 'w')
stdout.write('test')
stdout.close()