Eryk Sun added the comment:
> Windows also treats full-width spaces as a delimiter when parsing
> command line arguments.
CreateProcess has to parse the beginning of the command-line string if the
lpApplicationName parameter is omitted. According to the documentation, it
treats "white space" as a delimiter, but it doesn't actually say which
characters are in that set. We know for an unquoted name like
"python{character}spam" that it will try to execute python.exe if "{character}"
is parsed as a space. Otherwise we expect CreateProcess to fail with
ERROR_FILE_NOT_FOUND because it's looking for the non-existent file
"python{character}spam". Here's a test that checks all characters that Unicode
considers to be whitespace, which includes "ideographic space" (U+3000):
import os
import sys
import subprocess
space_chars = [chr(c) for c in range(sys.maxunicode) if chr(c).isspace()]
assert '\N{IDEOGRAPHIC SPACE}' in space_chars # U+3000
def get_create_delims():
assert not os.path.exists('spam')
filename = 'python{}spam'
basepath = os.path.dirname(sys.executable)
delims = []
for space in space_chars:
path = os.path.join(basepath, filename.format(space))
assert not os.path.exists(path)
try:
subprocess.check_output(path, stderr=subprocess.STDOUT)
except FileNotFoundError:
pass # not a delimiter
except subprocess.CalledProcessError:
delims.append(space)
else:
assert False, 'python.exe should have failed'
return delims
>>> get_create_delims()
['\t', ' ']
CreateProcess considers only space and horizontal tab as white-space
delimiters, at least on this Windows 10 system.
Otherwise Windows itself doesn't care about the command line. It's up to each
application to parse its command line however it wants. subprocess.list2cmdline
assumes an application uses argv from Microsoft's C runtime. The Windows shell
function CommandLineToArgvW is supposed to follow the same rules. The following
calls CommandLineToArgvW on a test command-line string for each character in
the space_chars set:
import ctypes
from ctypes import wintypes
shell32 = ctypes.WinDLL('shell32', use_last_error=True)
PLPWSTR = ctypes.POINTER(wintypes.LPWSTR)
shell32.CommandLineToArgvW.restype = PLPWSTR
def cmdline2argv(cmdline):
argc = ctypes.c_int()
pargv = shell32.CommandLineToArgvW(cmdline, ctypes.byref(argc))
if not pargv:
raise ctypes.WinError(ctypes.get_last_error())
return pargv[:argc.value]
def get_argv_delims():
cmdline = 'test{}space'
delims = []
for space in space_chars:
if len(cmdline2argv(cmdline.format(space))) > 1:
delims.append(space)
return delims
>>> get_argv_delims()
['\t', '\n', '\x0b', '\x0c', '\r', '\x1c', '\x1d', '\x1e', '\x1f', ' ']
In addition to space and horizontal tab, CommandLineToArgvW also considers line
feed, vertical tab, form feed, carriage return, file separator, group
separator, record separator, and unit separator to be white-space delimiters.
This disagrees with [1], which says it should be limited to space and
horizontal tab, like CreateProcess. Let's test this as well:
def get_msvc_argv_delims():
template = '"{}" -c "import sys;print(len(sys.argv))" test{}space'
delims = []
for space in space_chars:
cmdline = template.format(sys.executable, space)
out = subprocess.check_output(cmdline)
argc = int(out)
if argc > 2:
delims.append(space)
return delims
>>> get_msvc_argv_delims()
['\t', ' ']
Apparently CommandLineToArgvW is inconsistent with the C runtime in this case.
On my Windows 10 system, ideographic space (U+3000) is not generally a
command-line delimiter. That's not to say that some applications (and maybe
localized CRTs?) don't use it that way. But I don't think it's the place of the
subprocess module to handle it.
[1]: https://msdn.microsoft.com/en-us/library/17w5ykft
----------
nosy: +eryksun
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