Turn of globals in a function?

**Michael Spencer** · Jul 18 '05, 11:07 PM

Re: Turn of globals in a function?

Ron_Adam wrote:[color=blue]
> Is there a way to hide global names from a function or class?
>
> I want to be sure that a function doesn't use any global variables by
> mistake. So hiding them would force a name error in the case that I
> omit an initialization step. This might be a good way to quickly
> catch some hard to find, but easy to fix, errors in large code blocks.
>
> Examples:
>
> def a(x):
> # ...
> x = y # x is assigned to global y unintentionally .
> # ...
> return x
>
> def b(x):
> # hide globals somehow
> # ...
> x = y # Cause a name error
> # ...
> return x
>
>
> y = True
>
>[color=green][color=darkred]
>>>>a(False):[/color][/color]
>
> True
>
>[color=green][color=darkred]
>>>>b(False):[/color][/color]
>
> *** name error here ***
>
>
> Ron_Adam
>
>[/color]
For testing, you could simply execute the function in an empty dict:
[color=blue][color=green][color=darkred]
>>> a = "I'm a"
>>> def test():[/color][/color][/color]
... print a
...[color=blue][color=green][color=darkred]
>>> test()[/color][/color][/color]
I'm a[color=blue][color=green][color=darkred]
>>> exec test.func_code in {}[/color][/color][/color]
Traceback (most recent call last):
File "<input>", line 1, in ?
File "<input>", line 2, in test
NameError: global name 'a' is not defined[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

This would get more complicated when you wanted to test calling with parameters,
so with a little more effort, you can create a new function where the globals
binding is to an empty dict:
[color=blue][color=green][color=darkred]
>>> from types import FunctionType as function
>>> testtest = function(test.f unc_code, {})
>>> testtest()[/color][/color][/color]
Traceback (most recent call last):
File "<input>", line 1, in ?
File "<input>", line 2, in test
NameError: global name 'a' is not defined[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

HTH

Michael

**Bengt Richter** · Jul 18 '05, 11:07 PM

Re: Turn of globals in a function?

On Sat, 26 Mar 2005 20:01:28 GMT, Ron_Adam <radam2@tampaba y.rr.com> wrote:
[color=blue]
>
>Is there a way to hide global names from a function or class?
>
>I want to be sure that a function doesn't use any global variables by
>mistake. So hiding them would force a name error in the case that I
>omit an initialization step. This might be a good way to quickly
>catch some hard to find, but easy to fix, errors in large code blocks.
>
>Examples:
>
>def a(x):
> # ...
> x = y # x is assigned to global y unintentionally .
> # ...
> return x
>
>def b(x):
> # hide globals somehow
> # ...
> x = y # Cause a name error
> # ...
> return x
>
>[/color]
If you put the above def b in e.g. a_module.py,
and do a (untested ;-)

from a_module import b

instead of defining it locally, then the global references
from b (and whatever else you import from a_module)
should be to the global dict defined for a_module (i.e., its
outermost scope), not to the globals where you do the import.
[color=blue]
>y = True
>[color=green][color=darkred]
>>>>a(False):[/color][/color]
>True[/color]
Should work if you define a in place having same scope as the y assignment[color=blue]
>[color=green][color=darkred]
>>>>b(False):[/color][/color]
>*** name error here ***
>[/color]
UIAM it should do this if you import b as above.

Regards,
Bengt Richter

**Ron_Adam** · Jul 18 '05, 11:07 PM

Re: Turn of globals in a function?

On Sat, 26 Mar 2005 12:18:39 -0800, Michael Spencer
<mahs@telcopart ners.com> wrote:
[color=blue]
>Ron_Adam wrote:[color=green]
>> Is there a way to hide global names from a function or class?
>>
>> I want to be sure that a function doesn't use any global variables by
>> mistake. So hiding them would force a name error in the case that I
>> omit an initialization step. This might be a good way to quickly
>> catch some hard to find, but easy to fix, errors in large code blocks.
>>
>> Examples:
>>
>> def a(x):
>> # ...
>> x = y # x is assigned to global y unintentionally .
>> # ...
>> return x
>>
>> def b(x):
>> # hide globals somehow
>> # ...
>> x = y # Cause a name error
>> # ...
>> return x
>>
>>
>> y = True
>>
>>[color=darkred]
>>>>>a(False) :[/color]
>>
>> True
>>
>>[color=darkred]
>>>>>b(False) :[/color]
>>
>> *** name error here ***
>>
>>
>> Ron_Adam
>>
>>[/color]
>For testing, you could simply execute the function in an empty dict:
>[color=green][color=darkred]
> >>> a = "I'm a"
> >>> def test():[/color][/color]
> ... print a
> ...[color=green][color=darkred]
> >>> test()[/color][/color]
> I'm a[color=green][color=darkred]
> >>> exec test.func_code in {}[/color][/color]
> Traceback (most recent call last):
> File "<input>", line 1, in ?
> File "<input>", line 2, in test
> NameError: global name 'a' is not defined[color=green][color=darkred]
> >>>[/color][/color][/color]

I didn't know you could do that. Interesting. :)

I was hoping for something in line that could use with an assert
statement. But this is good too, I'll have to play around with it a
bit. Thanks.

Ron

[color=blue]
>This would get more complicated when you wanted to test calling with parameters,
>so with a little more effort, you can create a new function where the globals
>binding is to an empty dict:
>[color=green][color=darkred]
> >>> from types import FunctionType as function
> >>> testtest = function(test.f unc_code, {})
> >>> testtest()[/color][/color]
> Traceback (most recent call last):
> File "<input>", line 1, in ?
> File "<input>", line 2, in test
> NameError: global name 'a' is not defined[color=green][color=darkred]
> >>>[/color][/color]
>
>HTH
>
>Michael[/color]

**Ron_Adam** · Jul 18 '05, 11:07 PM

Re: Turn off globals in a function?

[color=blue]
>If you put the above def b in e.g. a_module.py,
>and do a (untested ;-)
>
> from a_module import b
>
>instead of defining it locally, then the global references
>from b (and whatever else you import from a_module)
>should be to the global dict defined for a_module (i.e., its
>outermost scope), not to the globals where you do the import.
>[color=green]
>>y = True
>>[color=darkred]
>>>>>a(False) :[/color]
>>True[/color]
>Should work if you define a in place having same scope as the y assignment[color=green]
>>[color=darkred]
>>>>>b(False) :[/color]
>>*** name error here ***
>>[/color]
>UIAM it should do this if you import b as above.
>
>Regards,
>Bengt Richter[/color]

Good suggestion. Thanks. I was somewhat aware of the modular scope,
but was looking for way to apply it on a more local level. Michael's
suggestion looks interesting for that.

Ron_Adam

**Oren Tirosh** · Jul 18 '05, 11:08 PM

Re: Turn of globals in a function?

Ron_Adam <radam2@tampaba y.rr.com> wrote in message news:<6qeb415iq qsor4biebk6rqj9 g6jv3lpt55@4ax. com>...[color=blue]
> Is there a way to hide global names from a function or class?
>
> I want to be sure that a function doesn't use any global variables by
> mistake. So hiding them would force a name error in the case that I
> omit an initialization step. This might be a good way to quickly
> catch some hard to find, but easy to fix, errors in large code blocks.[/color]

def noglobals(f):
.. import new
.. return new.function(
.. f.func_code,
.. {'__builtins__' :__builtins__},
.. f.func_name,
.. f.func_defaults ,
.. f.func_closure
.. )

You can use it with the Python 2.4 @decorator syntax:

@noglobals
def a(...):
.. # code here

Doing this for a class is a little more work. You will need dig inside
to perform this treatment on each method separately and handle new and
old-style classes a bit differently.

Note that this kind of function may declare globals. They will be
persistent but private to the function.

Oren

**Ron_Adam** · Jul 18 '05, 11:08 PM

Re: Turn of globals in a function?

On 26 Mar 2005 22:51:14 -0800, oren@REMOVETHIS 1.hishome.net (Oren
Tirosh) wrote:
[color=blue]
>Ron_Adam <radam2@tampaba y.rr.com> wrote in message news:<6qeb415iq qsor4biebk6rqj9 g6jv3lpt55@4ax. com>...[color=green]
>> Is there a way to hide global names from a function or class?
>>
>> I want to be sure that a function doesn't use any global variables by
>> mistake. So hiding them would force a name error in the case that I
>> omit an initialization step. This might be a good way to quickly
>> catch some hard to find, but easy to fix, errors in large code blocks.[/color]
>
>def noglobals(f):
>. import new
>. return new.function(
>. f.func_code,
>. {'__builtins__' :__builtins__},
>. f.func_name,
>. f.func_defaults ,
>. f.func_closure
>. )
>
>You can use it with the Python 2.4 @decorator syntax:
>
>@noglobals
>def a(...):
>. # code here[/color]

Cool! I haven't played with decorators yet. :)

I noticed the 'new' module is depreciated. It referred me to call the
object type directly instead. So this is probably the better way.

def noglobals(f):
return type(f)(
f.func_code,
{'__builtins__' :__builtins__},
f.func_name,
f.func_defaults ,
f.func_closure )

@noglobals
def a():
global x
try: x
except: x=0
x += 1
return x

x = 5
for n in range(10):
print a()
print x # x is still 5

So this is another, but longer, way to do a generator.

[color=blue][color=green][color=darkred]
>>> print type(a).__doc__[/color][/color][/color]
function(code, globals[, name[, argdefs[, closure]]])

Create a function object from a code object and a dictionary.
The optional name string overrides the name from the code object.
The optional argdefs tuple specifies the default argument values.
The optional closure tuple supplies the bindings for free variables.[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

What are 'free variables'?

And is there a way to directly read what names in a function are set
with the global statement? (Other than looking at the monitor. ;)

Ron_Adam

**Greg Ewing** · Jul 18 '05, 11:16 PM

Re: Turn of globals in a function?

Oren Tirosh wrote:[color=blue]
> def noglobals(f):
> . import new
> . return new.function(
> . f.func_code,
> . {'__builtins__' :__builtins__},
> . f.func_name,
> . f.func_defaults ,
> . f.func_closure
> . )[/color]

Be aware that this will render the function incapable
of seeing *any* globals at all, including other
functions and classes defined in the same module --
which you may find rather inconvenient!

--
Greg Ewing, Computer Science Dept,
University of Canterbury,
Christchurch, New Zealand

Greg Ewing's Home Page

http://www.cosc.canterbury.ac.nz/~greg

**Ron_Adam** · Jul 18 '05, 11:17 PM

Re: Turn of globals in a function?

On Thu, 31 Mar 2005 16:28:15 +1200, Greg Ewing
<greg@cosc.cant erbury.ac.nz> wrote:
[color=blue]
>Oren Tirosh wrote:[color=green]
>> def noglobals(f):
>> . import new
>> . return new.function(
>> . f.func_code,
>> . {'__builtins__' :__builtins__},
>> . f.func_name,
>> . f.func_defaults ,
>> . f.func_closure
>> . )[/color]
>
>Be aware that this will render the function incapable
>of seeing *any* globals at all, including other
>functions and classes defined in the same module --
>which you may find rather inconvenient![/color]

Developing this idea further...

This allows a programmer to specify what globals to allow read and or
writes.

Cheers,
Ron

#---start---
# useglobals.py

"""
A function to specify what globals and builtins
a function may access.
Author: Ronald Adam
"""

def useglobals(rw_g lobals=None, r_globals=None, builtins=True):
#import dis
import sys
write_list = []
read_list = []
if rw_globals != None:
rw_globals = rw_globals.repl ace(' ','')
write_list = rw_globals.spli t(',')
if r_globals != None:
r_globals = r_globals.repla ce(' ','')
read_list = r_globals.split (',')
if builtins == True:
read_list.exten d(dir(__builtin s__))
elif builtins != None:
builtins = builtins.replac e(' ','')
read_list.exten d(builtins.spli t(','))
# Add own name to read list.
read_list.appen d(sys._getframe (0).f_code.co_n ame)
read_list.exten d(write_list)
#print read_list, write_list
names = sys._getframe(1 ).f_code.co_nam es
code = sys._getframe(1 ).f_code.co_cod e
#print dis.disassemble (sys._getframe( 1).f_code)
i = 0
while i < len(code):
#print ord(code[i])
op = ord(code[i])
if op == 116: # dis.opmap['LOAD_GLOBAL']
oparg = ord(code[i+1]) + ord(code[i+2]) * 256
if str(names[oparg]) not in read_list:
raise NameError, "read from global name %s, detected"
% names[oparg]
elif op == 97: # dis.opmap['STORE_GLOBAL']
oparg = ord(code[i+1]) + ord(code[i+2]) * 256
if names[oparg] not in write_list:
raise NameError, "write to global name %s, detected" %
names[oparg]
if op >= 90: # dis.HAVE_ARGUME NT
i += 3 # Not sure if this is always the same?
else:
i += 1

if __name__ == '__main__':
"""
Test useglobals() function. Change values to test
for error catching.
"""

def a():
useglobals(rw_g lobals='x', r_globals='y,b' )
# This function can read or write 'x',
# Can read 'y', and function 'b',
# and can access all builtins.
global x
y = 5
x += y
x = b(x)
return x

def b(g):
useglobals('',' y,c','int')
# This function can only read 'y' and
# function 'c' in globals, and can
# only access 'int' in builtins.
g = g+y
c(int(g))
return g

def c(w):
useglobals(buil tins=None)
# This function has no builtins or globals.
w = w**2
return w

y = 4
x = 5
z = 6
print a(),x,y,z

#---end---

Turn of globals in a function?

Turn of globals in a function?

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