Peyman Askari wrote:
I want to write a function which imports modules the first time, and reloads
them afterwards, but I am running into problems with global variables and exec.
I will include a full script, but let me elaborate first.
Essentially what you need is
def import_or_reload():
"""assume we want to load or reload sys"""
if 'sys' in dir():
reload(sys)
else:
import sys
but this runs into the problem that sys is imported within the local scope of
the function, so you insert a global statement
def import_or_reload2():
"""Add 'global sys'"""
global sys
if 'sys' in dir():
reload(sys)
else:
import sys
'sys' is still not in dir() as dir() pertains to the local scope of the
function, but one can get around this by creating a local modules list and
adding the imported modules to it
def import_or_reload3():
"""Add 'global modules'"""
global sys
global modules
if 'sys' in modules:
reload(sys)
else:
import sys
modules.append('sys')
now lets add a parameter to the function signature, so any module name can be
passed as an argument and loaded
def import_or_reload4(module_name):
"""Add exec"""
exec 'global %s'%module_name
global modules
if module_name in modules:
exec 'reload(%s)'%module_name
else:
exec 'import %s'%module_name
exec 'modules.append(\'%s\')'%module_name
but this doesn't work as global does not cooperate with exec
is there a __reload__('X') function like there is an __import__(‘X’) function?
Also is there a better way to import modules at run time?
Cheers and here is the test script in case you can't access the attachment
def a():
global modules
global sys
import sys
modules.append('sys')
def b():
global modules
global sys
reload(sys)
def c(module_name):
global modules
exec 'global %s'%module_name
exec 'import %s'%module_name
modules.append(module_name)
def test():
global modules
global sys
#create the module list to contain all the modules
modules=[]
print 'originally dir() returns:'
print dir()
a()
print 'function a() properly imports the following module:'
print sys
print 'is %s in %s->%s'%('sys',modules,'sys' in modules)
b()
print 'function b() properly reloads the following module:'
print sys
print 'is %s still in %s->%s'%('sys',modules,'sys' in modules)
try:
c('os')
print 'function c() properly imports the following module:'
except:
print 'function c() failed to import module os'
print 'is %s in %s->%s'%('os',modules,'os' in modules)
try:
print os
print 'is %s still in %s->%s'%('os',modules,'os' in modules)
except:
print 'os was loaded, but is not visible outside of the scope of c()'
--- On Fri, 3/19/10, python-list-requ...@python.org
<python-list-requ...@python.org> wrote:
From: python-list-requ...@python.org <python-list-requ...@python.org>
Subject: Python-list Digest, Vol 78, Issue 192
To: python-list@python.org
Received: Friday, March 19, 2010, 7:05 AM
<snip>
(When starting a new thread, create a new message addressed to
python-list@python.org, do not just reply to an existing message, (or
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First comment. I would seriously try to avoid using reload() in
production code. The problems that can result are subtle. I use it for
debugging sessions, but not in real programs.
But I'll assume you have a use case (which would have been good to
explain), and have rejected the other possibilities.
Next, I'll point out that reloading sys isn't desirable, and it's one of
the specifically proscribed modules for reloading. But probably you
weren't really using sys, you were just sanitizing the code since you
knew we all had sys.
Next, if your reason for reloading is that you just changed the module
programmatically, and it might have been loaded by some other module (as
sys is, for example, long before your code starts), then you're not
checking in the right place. Instead of looking at your own global
space, you should be looking at sys.modules to decide whether something
has been loaded.
Perhaps the function you're looking for is imp.load_module()
DaveA
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