为什么以下python代码不打印到文件

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()