Develop Reference

Python can't handle Windows long paths with parent directory parts

I'm trying to use .. in a Windows long filename within Python and it is producing unexpected results.
Here is the output from the Python REPL:
Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.path.exists(u'\\\\?\\C:\\BitBucket\\crab6\\product\\installer\\windows\\..\\usage.txt')
False
>>> os.path.exists(u'\\\\?\\C:\\BitBucket\\crab6\\product\\installer\\usage.txt')
True
(I realize the path above isn't over 260 characters and therefore the long path syntax is unnecessary, but for the purposes of this post I've made it more manageable. The outcome is the same with very long paths.)
Has anyone else encountered this, and is it a purposeful limitation of long filenames?

Run scons on Windows 10 environment with Python 2.7 and Python 3

How can I run scons on Windows 10 when Python 3.6.1 and Python 2.7.13 is installed? When typing python into my command window I get the following output:
Python 3.6.1 (v3.6.1:69c0db5, Mar 21 2017, 18:41:36) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>
Since I personally use Python 3.6.x this is fine for me and I do not want to change this.
When typing py -2 into my command window I get the following output:
Python 2.7.13 (v2.7.13:a06454b1afa1, Dec 17 2016, 20:42:59) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>
scons does not work with Python 3.x. It needs to be executed with Python 2.7.x. How can I "tell" scons to use Python 2.7.x?
When I just type scons into the command prompt I get the following output:
PS C:\dev\projectX> scons
Fatal Python error: Py_Initialize: unable to load the file system codec
ModuleNotFoundError: No module named 'encodings'
Current thread 0x00007050 (most recent call first):

Try Changing line 23 in scons.bat from:
python "%scriptname%" %*
to
py -2 "%scriptname%" %*
Note that work on getting SCons to run under both py 2 and py 3.5+ is mostly done and should be released in the next month (or so)

Before running scons in Powershell, amend the PATH environment variable to put your Python 2.7 installation at the front. Something like:
SET PATH=C:\Python27;%path%

Syntax error in command line while executing python programme

I have just started using python3.3. The shell looks like this:
Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:06:53) [MSC v.1600 64 bit (AMD64)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> print ("hello world")
It prints hello world correclty, but in the command line it shows error in line 1 (i.e Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:06:53) [MSC v.1600 64 bit (AMD64)] on win32 ) declaring it as a syntax error.
What is the problem??

You are specifying the syntax incorrectly on the command line. The correct syntax is:
$ python3 -c 'print ("hello world")'

That's not an error. That's what appears when you open the interactive interpreter by typing $ python3, telling you what version of python you have and other details (such as the date).

Is there easy way to prevent echo from input?

How to prevent echo from input ??
Have tried "getpass()" but no luck.
On Windows IDLE, it doesn't work
Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> import getpass
>>> p = getpass.getpass(prompt="Input: ")
Warning: Password input may be echoed.
Input: abc <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< It still echos..
On the terminal of the Windows, it works
Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (In
tel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import getpass
>>> p = getpass.getpass(prompt="Input: ")
Input:
>>>
Is there a easy way to prevent echo from input ?

I'm assuming your first example there is in IDLE.
From getpass.win_getpass():
if sys.stdin is not sys.__stdin__:
return fallback_getpass(prompt, stream)
IDLE replaces sys.stdin with a different object. getpass detects that somebody has wrapped stdin and fails for security reasons.
See: http://bugs.python.org/issue9290

os.exec on Windows

I have a script that calls os.execvp into another Python instance. After doing this, I appear to be attached to a cmd.exe instance, not the Python instance I just created. The Python instance responds to Ctrl+C however.
H:\bin>Python 3.2.1 (default, Jul 10 2011, 21:51:15) [MSC v.1500
32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print('hi')
Can't find file ('hi')
H:\bin>
H:\bin>
KeyboardInterrupt
>>> echo hi
hi
The call to exec:
from sys import argv
os.execvp('python', argv)
How do I replace the original Python instance with the new one, as per the behaviour one might see on Linux?

On Unix executing binaries is split into two stages - fork(3) to clone current process and exec(3) to load executable into address space. On windows there is only CreateProcess which does the same thing as fork+exec.
For portability your best bet is to use subprocess.Popen (which also does proper filename quoting on Windows unlike os.* counterparts) as in http://docs.python.org/library/subprocess.html#replacing-the-os-spawn-family