Python code for testing well parenthesized expression

[David Smith]

Jeremy Sanders wrote:
> candide wrote:
> 
>> I'm trying to implement in Python a function testing if an expression is
>> well parenthesized. For instance the expression "zx4er(1(er(Yy)ol)ol)ik"
>> is correctly parenthesized but this one "zx(4er(1(er(Yy)ol)ol)ik" is not.
>>
>> My code follows at the end.
>>
>> If you have a better algorithm or a better Python code (I'm a beginner in
>> the Python world), don't hesitate ...
> 
> Don't you want to just test that the number of "("s equals the number of 
> ")"s or am I missing the point?
> 
>>>> a='aAAA(bbb(cc)))'
>>>> a.count('(') == a.count(')')
> 
> Jeremy
> 

Using straight counting, )z))ab(c(ew( would be well parenthesized.  I
suspect a better way would be to iterate over the string using a balance
counter that increases 1 for every open, decreases 1 for every close.  A
negative balance at any moment would indicate an error as well as an
ending balance greater than 0.

--David