Cmd and Git bash have a different result when run a Python code

Question

Platform: Git bash MINGW64, Windows 7, 64 CMD
When I run a Python code from Learn Python The Hard Way ex11. The code is simple.

print "How old are you?",
age = raw_input()
print "How tall are you?",
height = raw_input()
print "How much do you weigh?",
weight = raw_input()

print "So, you're %r old, %r tall and %r heavy." % (
    age, height, weight)

But they have different result in CMD and Git bash. When I run it using Git bash, the raw_input() will run first.

When you input 3 answers, then it will show the 4 print in the end. When I run it in CMD, it shows normally, one print, one raw_input().

Can somebody explain it?

EDIT: Actually, my goal is to explain the reason, not to solve this with flush. So It is different with this question

Asked By: naifan

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Source

Answer 1

So I had a look at this and tried a couple of different ways of writing what you have there, and they all acted the same way. Digging into it some more I came across https://code.google.com/p/mintty/issues/detail?id=218. Key from this is andy.koppe’s reply:

The key to the problem is that stdout’s default buffering mode depends on the type of device: unbuffered for a console, buffered for a pipe. This means that in a console the output will appear immediately, whereas in mintty it will only appear once the buffer is either full or flushed, as happens at the end of main().

Windows Console prints text to the screen as soon as possible, while mingw (git bash) will wait until the application tells it to update the screen.

So to get it to behave the same in both, you will need to flush the buffer to the screen after each print. How to flush output of Python print? has information about how to do this, but it comes down to the following:

import sys

print "How old are you?"
sys.stdout.flush()
age = raw_input()
print "How tall are you?"
sys.stdout.flush()
height = raw_input()
print "How much do you weigh?"
sys.stdout.flush()
weight = raw_input()

print "So, you're %r old, %r tall and %r heavy." % (age, height, weight)

Alternatively you can run it in mingw using the -u command, which will stop python from buffering output in mingw.

python -u file.py

Answered By: Mitch Pomery

Cmd and Git bash have a different result when run a Python code

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