Issue 2470: Need fixer for dl (removed) -> ctypes module

r61837 removed the dl module.  It needs a 2to3 fixer written to use ctypes.

Is it possible to write one? I'm skeptical.

Can you list the mapping you'd like to see? I've never used dl or
ctypes, so I'm not immediately sure how to port from one to the other.

In the simplest case, convert

import dl
libc = dl.open("libc.so.6")
iconv = libc.call("iconv_open", "ISO-8859-1", "ISO-8859-2")
print(iconv)

to

import ctypes
libc = ctypes.CDLL("libc.so.6")
iconv = libc.iconv_open("ISO-8859-1", "ISO-8859-2")
print(iconv)

Notice that <dlobject>.call has up to 11 arguments, the first one being
the function name.

Thomas, is it the case that all calls to dl.call can be converted to a
ctypes call without parameter conversion? dl supports these parameter
types:
- byte string, passed as char*
- integers, passed as int
- None, passed as NULL

> In the simplest case, convert
> 
> import dl
> libc = dl.open("libc.so.6")
> iconv = libc.call("iconv_open", "ISO-8859-1", "ISO-8859-2")
> print(iconv)
> 
> to
> 
> import ctypes
> libc = ctypes.CDLL("libc.so.6")
> iconv = libc.iconv_open("ISO-8859-1", "ISO-8859-2")
> print(iconv)
> 
> Notice that <dlobject>.call has up to 11 arguments, the first one being
> the function name.
> 
> Thomas, is it the case that all calls to dl.call can be converted to a
> ctypes call without parameter conversion? dl supports these parameter
> types:
> - byte string, passed as char*
> - integers, passed as int
> - None, passed as NULL

Yes, this is correct.

Thomas Heller schrieb:
> Thomas Heller <theller@ctypes.org> added the comment:
> 
>> In the simplest case, convert
>> 
>> import dl
>> libc = dl.open("libc.so.6")
>> iconv = libc.call("iconv_open", "ISO-8859-1", "ISO-8859-2")
>> print(iconv)
>> 
>> to
>> 
>> import ctypes
>> libc = ctypes.CDLL("libc.so.6")
>> iconv = libc.iconv_open("ISO-8859-1", "ISO-8859-2")
>> print(iconv)
>> 

Currently, in py3k, ctypes only passed bytes objects as char*; so
the strings should be translated to bytes literals:

import ctypes
libc = ctypes.CDLL("libc.so.6")
iconv = libc.iconv_open(b"ISO-8859-1", b"ISO-8859-2")
#                       ^              ^
print(iconv)

What's the status of this?

If nobody else is interested in or currently in the process of making a
fixer for this, I can do it. I'm not sure if I completely understand the
changes I need to make though. Importing dl needs to be replaced by
importing ctypes, calls to dl.open() need to be replaced by calls to
ctypes.CDLL(), and calls to call() from an open dl object need to be
replaced to calls to funcname, where funcname is the first argument to
call(). Also, any strings in the other arguments should be preceded with
b to make them byte objects. Is this all that needs doing or am I
missing something else? Are there more complicated cases that I should
also take into account?

I'd prefer it if someone better-versed in ctypes/dl wrote this fixer (or
at the very least, someone with access to Windows to test the translation).

I can review and try out the fixer if someone provides a patch.  OTOH I
have never used the dl module.

Note that dl exposed a lot of RTLD_ constants that ctypes does not yet,
so there should be a patch for ctypes also.

for the RTLD_ constants, refer to issue #13226.

Being open for four years, this is hardly critical.

messages: + msg158724