How to read Unicode characters from command-line arguments in Python on Windows

Question

I want my Python script to be able to read Unicode command line arguments in Windows. But it appears that sys.argv is a string encoded in some local encoding, rather than Unicode. How can I read the command line in full Unicode?

Example code: argv.py

import sys

first_arg = sys.argv[1]
print first_arg
print type(first_arg)
print first_arg.encode("hex")
print open(first_arg)

On my PC set up for Japanese code page, I get:

C:\temp>argv.py "PC・ソフト申請書08.09.24.doc"
PC・ソフト申請書08.09.24.doc
<type 'str'>
50438145835c83748367905c90bf8f9130382e30392e32342e646f63
<open file 'PC・ソフト申請書08.09.24.doc', mode 'r' at 0x00917D90>

That's Shift-JIS encoded I believe, and it "works" for that filename. But it breaks for filenames with characters that aren't in the Shift-JIS character set—the final "open" call fails:

C:\temp>argv.py Jörgen.txt
Jorgen.txt
<type 'str'>
4a6f7267656e2e747874
Traceback (most recent call last):
  File "C:\temp\argv.py", line 7,
in <module>
    print open(first_arg)
IOError: [Errno 2] No such file or directory: 'Jorgen.txt'

Note—I'm talking about Python 2.x, not Python 3.0. I've found that Python 3.0 gives sys.argv as proper Unicode. But it's a bit early yet to transition to Python 3.0 (due to lack of 3rd party library support).

Update:

A few answers have said I should decode according to whatever the sys.argv is encoded in. The problem with that is that it's not full Unicode, so some characters are not representable.

Here's the use case that gives me grief: I have enabled drag-and-drop of files onto .py files in Windows Explorer. I have file names with all sorts of characters, including some not in the system default code page. My Python script doesn't get the right Unicode filenames passed to it via sys.argv in all cases, when the characters aren't representable in the current code page encoding.

There is certainly some Windows API to read the command line with full Unicode (and Python 3.0 does it). I assume the Python 2.x interpreter is not using it.

Answer 1

Check this question asked here on Stack Overflow, it should provide the answer to your question:

http://stackoverflow.com/questions/477061/how-to-read-unicode-input-and-compare-unicode-strings-in-python

Answer 2

The command line might be in Windows encoding. Try decoding the arguments into unicode objects:

args = [unicode(x, "iso-8859-9") for x in sys.argv]

Answer 3

Try this:

import sys
print repr(sys.argv[1].decode('UTF-8'))

Maybe you have to substitute CP437 or CP1252 for UTF-8. You should be able to infer the proper encoding name from the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\CodePage\OEMCP

Answer 4

Here is a solution that is just what I'm looking for, making a call to the Windows GetCommandLineArgvW function:
Get sys.argv with Unicode characters under Windows (from ActiveState)

But I've made several changes, to simplify its usage and better handle certain uses. Here is what I use:

win32_unicode_argv.py

"""
win32_unicode_argv.py

Importing this will replace sys.argv with a full Unicode form.
Windows only.

From this site, with adaptations:
      http://code.activestate.com/recipes/572200/

Usage: simply import this module into a script. sys.argv is changed to
be a list of Unicode strings.
"""


import sys

def win32_unicode_argv():
    """Uses shell32.GetCommandLineArgvW to get sys.argv as a list of Unicode
    strings.

    Versions 2.x of Python don't support Unicode in sys.argv on
    Windows, with the underlying Windows API instead replacing multi-byte
    characters with '?'.
    """

    from ctypes import POINTER, byref, cdll, c_int, windll
    from ctypes.wintypes import LPCWSTR, LPWSTR

    GetCommandLineW = cdll.kernel32.GetCommandLineW
    GetCommandLineW.argtypes = []
    GetCommandLineW.restype = LPCWSTR

    CommandLineToArgvW = windll.shell32.CommandLineToArgvW
    CommandLineToArgvW.argtypes = [LPCWSTR, POINTER(c_int)]
    CommandLineToArgvW.restype = POINTER(LPWSTR)

    cmd = GetCommandLineW()
    argc = c_int(0)
    argv = CommandLineToArgvW(cmd, byref(argc))
    if argc.value > 0:
        # Remove Python executable and commands if present
        start = argc.value - len(sys.argv)
        return [argv[i] for i in
                xrange(start, argc.value)]

sys.argv = win32_unicode_argv()

Now, the way I use it is simply to do:

import sys
import win32_unicode_argv

and from then on, sys.argv is a list of Unicode strings. The Python optparse module seems happy to parse it, which is great.

Answer 5

Dealing with encodings is very confusing.

I believe if your inputing data via the commandline it will encode the data as whatever your system encoding is and is not unicode. (Even copy/paste should do this)

So it should be correct to decode into unicode using the system encoding:

import sys

first_arg = sys.argv[1]
print first_arg
print type(first_arg)

first_arg_unicode = first_arg.decode(sys.getfilesystemencoding())
print first_arg_unicode
print type(first_arg_unicode)

f = codecs.open(first_arg_unicode, 'r', 'utf-8')
unicode_text = f.read()
print type(unicode_text)
print unicode_text.encode(sys.getfilesystemencoding())

running the following Will output: Prompt> python myargv.py "PC・ソフト申請書08.09.24.txt"

PC・ソフト申請書08.09.24.txt
<type 'str'>
<type 'unicode'>
PC・ソフト申請書08.09.24.txt
<type 'unicode'>
?日本語

Where the "PC・ソフト申請書08.09.24.txt" contained the text, "日本語". (I encoded the file as utf8 using windows notepad, I'm a little stumped as to why there's a '?' in the begining when printing. Something to do with how notepad saves utf8?)

The strings 'decode' method or the unicode() builtin can be used to convert an encoding into unicode.

unicode_str = utf8_str.decode('utf8')
unicode_str = unicode(utf8_str, 'utf8')

Also, if your dealing with encoded files you may want to use the codecs.open() function in place of the built-in open(). It allows you to define the encoding of the file.

codecs.open: http://docs.python.org/library/codecs.html?#codecs.open

If I'm miss-understanding something please let me know.

If you haven't already I recommend reading Joel's article on unicode and encoding: http://www.joelonsoftware.com/articles/Unicode.html