Why does naming a file 'con.txt' in windows make Python write to console, not file?

Question

I need help debugging some odd file behavior in Python. Take the following script (write_con.py):

f=open('con.txt','w')
f.write('hi')

In Linux, this creates a file called con.txt with the contents hi. In Windows this writes hi to the console and does not create a file. I've tried this with Python 2.5.1, 2.6.3, 2.6.5, and 2.7.2. Example run:

C:\Users\rpsharp> C:\Python27\python.exe .\write_con.py
hiC:\Users\rpsharp> C:\Python25\python.exe .\write_con.py
hiC:\Users\rpsharp>

Yet a file named anything other than something that starts with con works fine (write_other_con.py):

f=open('other_con.txt','w')
f.write('hi')

Here's a run:

C:\Users\rpsharp> C:\Python25\python.exe .\write_other_con.py
C:\Users\rpsharp> type .\other_con.txt
hi

What's going on that causes windows versions of python to write to the console when the prefix of the named file is con?

Answer 1

Legacy. In DOS, writing to a file called "CON" writes it to the console instead; Windows continues this tradition.

Answer 2

You have to check the Wikipedia Filename page. It has a table containing the reserved characters for quite a lot of file systems.

In Windows and DOS utilities, some words might also be reserved and can not be used as filenames. For example, DOS Device file:

CON, PRN, AUX, CLOCK$, NUL COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9 LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9.

Answer 3

This is not a Python error, but a Windows naming convention. There are a list of reserved keywords that Windows will not allow you to save files or folders as, including CON, PRN, AUX, CLOCK$, NUL COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, LPT9.