New submission from David M. Rogers <dmr...@sandia.gov>:
Python Devs,
There is an issue relating to variable lookup using exec from within
multiprocessing's fork()-ed process. I'm attempting to use the forked process
as a generic remote python shell, but exec is unable to reach variables from
within functions. This issue makes it impossible to define a function which
uses un-passed variables defined in the remote process.
The simplest way to reproduce the error is:
--- err.py ---
from multiprocessing import Process, Pipe
def run_remote(con, name):
my_name = name
for i in range(2):
code = con.recv()
exec code
me, he = Pipe()
p = Process(target=run_remote,
args=(he, "Sono Inglese de Gerrards Cross."))
p.start()
me.send("print my_name") # works
me.send("""
def show_name():
print my_name
show_name() # doesn't work
""")
--- end err.py ---
This program prints:
$ python2.6 err.py
Sono Inglese de Gerrards Cross.
Process Process-1:
Traceback (most recent call last):
File "/sw/lib/python2.6/multiprocessing/process.py", line 232, in _bootstrap
self.run()
File "/sw/lib/python2.6/multiprocessing/process.py", line 88, in run
self._target(*self._args, **self._kwargs)
File "err.py", line 7, in run_remote
exec code
File "<string>", line 4, in <module>
File "<string>", line 3, in show_name
NameError: global name 'my_name' is not defined
I'm using Mac OSX (10.6.8) and
Python 2.6.5 (r265:79063, Sep 23 2010, 14:05:02)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
The issue (with the same traceback) also occurs for:
Python 2.7 (r27:82500, Sep 29 2010, 15:34:46)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Using exactly the same set of exec calls locally results in the correct
behavior.
--- noerr.py ---
my_name = "Sono Inglese de Gerrards Cross."
exec "print my_name"
exec """
def show_name():
print my_name
show_name()
"""
--- end noerr.py ---
----------
components: None
messages: 159764
nosy: frobnitzem
priority: normal
severity: normal
status: open
title: NameError Issue in Multiprocessing
versions: Python 2.6
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue14704>
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