How do I do Variable Variables in Python?

Question

How do I accomplish this in Python? Here is an elaborative manual entry, for instance :http://us3.php.net/manual/en/language.variables.variable.php

I hear this is a bad idea in general though, and it is a security hole in PHP. I'm curious if anyone knows how as well?

Answer 1

Use dictionaries to accomplish this. Dictionaries are stores of keys and values.

>>> dict = { 
    'x': 1, 
    'y': 2, 
    'z': 3
}
>>> dict
{'y': 2, 'x': 1, 'z': 3}
>>> dict['y']
2

You can use variable key names to achieve the effect of variable variables without the security risk.

>>> x = 'spam'
>>> z = { x: 'eggs' }
>>> z['spam']
'eggs'

Make sense?

Answer 2

Whenever you want to use variable variables, it's probably better to use a dictionary. So instead of writing

$foo = "bar"
$$foo = "baz"

you write

mydict = {}
foo = "bar"
mydict[foo] = "baz"

This way you won't accidentally overwrite previously existing variables (which is the security aspect) and you can have different "namespaces".

Answer 3

can be easily accomplished with built-in getattr.

getattr(obj, 'foobar')

Answer 4

It's not a good idea. If you are accessing a global variable you can use globals()

>>> a = 10
>>> globals()['a']
10

If you want to access a variable in the local scope you can use locals()

A better solution is to use getattr or store your variables in a dictionary and then access them by name.

Answer 5

You could also use exec and eval:

newvar = 'x'
newvalue = 12
exec('%s=%d') % (newvar, newvalue)
#this will print 12
print x
#this will print 12 as well
print eval(newvar)