how to convert string to list or tuple

[flyaflya]

a = "(1,2,3)"
I want convert a to tuple:(1,2,3),b ut tuple(a) return ('(', '1', ',',
'2', ',', '3', ')') not (1,2,3)

[Duncan Booth]

Steven Bethard wrote:

Duncan Booth wrote:

any new style class you have defined and call any of its methods with
whatever arguments I wish.

Any new style class that I've defined? Or just any one I pass in as
part of dict(__builtins __=None, ...)? If the former, could you
elaborate? If the latter, then yes, I can see the problem. However
for the case where all you pass in is dict(__builtins __=None), is
there still a risk? Note that in the OP's case, all that is necessary
is constant parsing, so no names need to be available.

Any new style class you have defined is accessible through
object.__subcla sses__(), and as I showed object itself is always accessible
through {}.__class__.__ bases__[0].

I'm assuming that the source code for your program is available. That means
I can find the name of an interesting class which has a method that does
something destructive, and call it.

e.g. Assuming that the MyDatabase class does something nasty to a file:

class MyDatabase(obje ct): def __init__(self, filename):
self.filename = filename
def initialise(self ):
print "Splat %s" % self.filename

eval('''[ cls for cls in {}.__class__.__ bases__[0].__subclasses__ ()

if 'MyDatabase' in `cls`
][0]('importantfile ').initialise() ''', dict(__builtins __=None))
Splat importantfile

[Steven Bethard]

Duncan Booth wrote:

e.g. Assuming that the MyDatabase class does something nasty to a file:

class MyDatabase(obje ct):
def __init__(self, filename):
self.filename = filename
def initialise(self ):
print "Splat %s" % self.filename
eval('''[ cls for cls in {}.__class__.__ bases__[0].__subclasses__ ()

if 'MyDatabase' in `cls`
][0]('importantfile ').initialise() ''', dict(__builtins __=None))
Splat importantfile

Interestingly, I don't seem to be able to create a file object as a
class attribute in restricted mode:

py> class C(object):
.... def __init__(self):
.... self.f = file('temp.txt' , 'w')
....
py> eval('''[ cls for cls in {}.__class__.__ bases__[0].__subclasses__ ()
if cls.__name__ == 'C'][0]().f.write("stu ff")''', dict(__builtins __=None))
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
File "<string>", line 0, in ?
AttributeError: 'C' object has no attribute 'f'
py> eval('''[ cls for cls in {}.__class__.__ bases__[0].__subclasses__ ()
if cls.__name__ == 'C'][0]().__dict__''', dict(__builtins __=None))
{}

I don't get an error for calling the file constructor, but the f
attribute is never set AFAICT.

STeVe

[Duncan Booth]

Steven Bethard wrote:

Interestingly, I don't seem to be able to create a file object as a
class attribute in restricted mode:

py> class C(object):
... def __init__(self):
... self.f = file('temp.txt' , 'w')
...
py> eval('''[ cls for cls in
{}.__class__.__ bases__[0].__subclasses__ () if cls.__name__ ==
'C'][0]().f.write("stu ff")''', dict(__builtins __=None)) Traceback
(most recent call last):
File "<interacti ve input>", line 1, in ?
File "<string>", line 0, in ?
AttributeError: 'C' object has no attribute 'f'
py> eval('''[ cls for cls in
{}.__class__.__ bases__[0].__subclasses__ () if cls.__name__ ==
'C'][0]().__dict__''', dict(__builtins __=None)) {}

Weird. I copied and paste your class and eval exactly (apart from deleting
the ... prompts) and it worked exactly as expected: writing 'stuff' to
temp.txt. (Python 2.4)

[Fuzzyman]

flyaflya wrote:

a = "(1,2,3)"
I want convert a to tuple:(1,2,3),b ut tuple(a) return ('(', '1', ',',
'2', ',', '3', ')') not (1,2,3)

Probably a bit late... but there's always listquote - It's part of the
pythonutils module.

http://www.voidspace.org.uk/python/pythonutils.html

It will turn strings to lists, including nested lists.

Best Regards,

Fuzzy
http://www.voidspace.org.uk/python

[Steven Bethard]

Duncan Booth wrote:

Steven Bethard wrote:

Interestingly , I don't seem to be able to create a file object as a
class attribute in restricted mode:

py> class C(object):
... def __init__(self):
... self.f = file('temp.txt' , 'w')
...
py> eval('''[ cls for cls in
{}.__class__. __bases__[0].__subclasses__ () if cls.__name__ ==
'C'][0]().f.write("stu ff")''', dict(__builtins __=None)) Traceback
(most recent call last):
File "<interacti ve input>", line 1, in ?
File "<string>", line 0, in ?
AttributeErro r: 'C' object has no attribute 'f'
py> eval('''[ cls for cls in
{}.__class__. __bases__[0].__subclasses__ () if cls.__name__ ==
'C'][0]().__dict__''', dict(__builtins __=None)) {}

Weird. I copied and paste your class and eval exactly (apart from deleting
the ... prompts) and it worked exactly as expected: writing 'stuff' to
temp.txt. (Python 2.4)

So, I played around with this a little bit. If I start up a new
interpreter and type it in like above, I get the behavior you do. What
I had actually done (abbreviated) was:

py> class C(object):
.... pass
....
py> class C(object):
.... def __init__(self):
.... self.f = file('temp.txt' , 'w')
....
py> eval('''[ cls for cls in {}.__class__.__ bases__[0].__subclasses__ ()
if cls.__name__ == 'C'][0]().f.write("stu ff")''', dict(__builtins __=None))
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
File "<string>", line 0, in ?
AttributeError: 'C' object has no attribute 'f'

And the problem with this is that both __main__.C objects are now
subclasses of object:

py> eval('''[ cls for cls in {}.__class__.__ bases__[0].__subclasses__ ()
if cls.__name__ == 'C']''', dict(__builtins __=None))
[<class '__main__.C'>, <class '__main__.C'>]

So I was getting the wrong __main__.C object. Sorry for the confusion!

Now, even using this technique, *your* code can't call the file constructor:

py> class C(object):
.... def __init__(self):
.... self.file = file
....
py> eval('''[ cls for cls in {}.__class__.__ bases__[0].__subclasses__ ()
if cls.__name__ == 'C'][-1]().file("temp.t xt", "w")''',
dict(__builtins __=None))
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
File "<string>", line 0, in ?
IOError: file() constructor not accessible in restricted mode

But unless the person eval-ing your code *only* writes immaculate code I
can see that you can probably screw them. ;) I wonder why
__subclasses__ isn't a restricted attribute... Is it ever used for
something that isn't evil? ;)

STeVe

[Ruud de Jong]

Steven Bethard schreef:

But unless the person eval-ing your code *only* writes immaculate code I
can see that you can probably screw them. ;) I wonder why
__subclasses__ isn't a restricted attribute... Is it ever used for
something that isn't evil? ;)

STeVe

Completely off topic, but I just cannot resist showing off.
Some time ago I used __subclasses__ in a way that is not evil. I think.

The details are described in the following thread:
http://groups.google.nl/group/comp.l...ccb986c66cdc1/

A summary: I used __subclasses__ to apply the Chain-of-Responsibility
pattern to object creation. The code would appear to instantiate
an object of the root of a class hierarchy, but the actual object
that was created would be an instance of a subclass.

So to get back to your question: yes, there are non-evil
uses for __subclasses__. Weird perhaps, but non-evil.
Non-standard, sure . Too clever for my own good, very likely.

Regards,

Ruud

--
Ruud de Jong

'@'.join('.'.jo in(s) for s in (['ruud','de','jo ng'],['tiscali','nl']))

[Duncan Booth]

Ruud de Jong wrote:

Steven Bethard schreef:

But unless the person eval-ing your code *only* writes immaculate
code I can see that you can probably screw them. ;) I wonder why
__subclasses__ isn't a restricted attribute... Is it ever used for
something that isn't evil? ;)

STeVe

Completely off topic, but I just cannot resist showing off.
Some time ago I used __subclasses__ in a way that is not evil. I
think.

The details are described in the following thread:
http://groups.google.nl/group/comp.l...ead/thread/5c1
ccb986c66cdc1/

A summary: I used __subclasses__ to apply the Chain-of-Responsibility
pattern to object creation. The code would appear to instantiate
an object of the root of a class hierarchy, but the actual object
that was created would be an instance of a subclass.

So to get back to your question: yes, there are non-evil
uses for __subclasses__. Weird perhaps, but non-evil.
Non-standard, sure . Too clever for my own good, very likely.

I've done almost exactly the same thing. The base class uses __subclasses__
to find the best matching subclass based on the factory parameters. In my
case I was retrieving files from the web, so I had a base Handler class and
created HtmlHandler, ImageHandler &c.

class Handler(object) :
'''Class to process files'''
__map = {}

@classmethod
def _resolveClass(k lass, isdir, name):
map = Handler.__map
if not map:
for c in klass.__subclas ses__():
for ext in c.Extensions:
map['.'+ext.lower()] = c

if isdir:
klass = FolderHandler
else:
ext = os.path.splitex t(name)[1].lower()
if ext not in map:
map[ext] = DefaultHandler

klass = map[ext]
return klass(name)

@classmethod
def fromPathname(kl ass, name, path, uri, db):
isdir = os.path.isdir(o s.path.join(pat h, name))
obj = klass._resolveC lass(isdir, name)
obj._initialize (name, path, uri, db)
return obj

@classmethod
def fromUrl(klass, uri, text, db=None):
... and so on ...

and then subclasses such as:

class ImageHandler(Ha ndler):
Extensions = ('jpg', 'jpeg', 'gif', 'png')
type = 'Image'

class DefaultHandler( Handler):
Extensions = ('',)
type = 'Ignored'

This also contains the only code I think I've written with a class
definition in a for loop:

# General categories
EXTENSIONS = {
'js': 'javascript',
'php': 'php',
'doc': 'Word Document',
'xls': 'Spreadsheet',
'ppt': 'Powerpoint',
'css': 'Stylesheet',
'swf': 'Flash',
'pdf': 'File',
'rtf': 'File',
'zip': 'File',
}

Classes = []
for ext in EXTENSIONS:
class GeneralHandler( Handler):
Extensions = (ext,)
type = EXTENSIONS[ext]

Classes.append( GeneralHandler)