Question

Possible Duplicate:
How to programmatically set a global (module) variable?

I have a class called Variable defined as so:

class Variable():
    def __init__(self, name):
        self.name = name
        self._value = None
    def value(self):
        return self._value
    def __repr__(self):
        return self.name

I want to create 26 capital single letter instances of Variable like this:

A = Variable('A')
B = Variable('B')
...
Z = Variable('Z')

So far I’ve tried various solutions, and the best I’ve come up with is:

from string import uppercase
for char in uppercase:
    exec "%s = %s" % (char, Variable(str(char))) in None

However, this doesn’t run and gives me this error:

Traceback (most recent call last):
  File "C:\Users\Administrator\Dev\python\truthtable\truthtable.py", line 7, in <module>
    exec "%s = %s" % (char, Variable(str(char))) in None
  File "<string>", line 1, in <module>
NameError: name 'A' is not defined

What am I doing wrong?

Answer 1

from string import uppercase
_g = globals()
for char in uppercase:
    _g[char] = Variable(char)

Whether this is a good idea remains questionable 🙂

This only works for globals() (i.e. module level assignments), as the language definition explicitly states that modifying the dictionary returned by locals() may not actually change the value of any local variables.

You can also do something similar with the __dict__ of a class or instance.