Bob Rogers wrote:
> Given this class:
>
> class C(object):
> def set_x(self, x):
> self._x = x
>
> def get_x(self):
> return self._x
>
> x = property(get_x, set_x)
>
>
> This use of compile() and eval() works as I expected it to:
>
> c = C()
> c.x = 5000
> n = '\'five thousand\''
> code = compile('c.x = ' + n, '<input>', 'exec')
> print 'before ', c.x
> eval(code)
> print 'after ', c.x
I believe it is an implementation accident that this works.
>
> But this, using eval() without compile(), does not:
>
> c = C()
> c.x = 5000
> n = '\'five thousand\''
> print 'before ', c.x
> eval('c.x = ' + n)
> print 'after ', c.x
>
> It gives:
>
> before 5000
> Traceback (most recent call last):
> File "./r.py", line 16, in ?
> eval('c.x = ' + n)
> File "<string>", line 1
> c.x = 'five thousand'
> ^
> SyntaxError: invalid syntax
>
> Could someone please explain just what is going on here, and whether it
> is possible to dispense with the compile step and use eval() alone
> while setting a property?
Use
eval(s)
to evaluate an expression and
exec s
to execute a statement.
Peter
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