Python balanced Parenthesis help

Question

I can't find out why it doesn't make the length of expression into 0 to print True for ssome test cases, anyone know what's missing?

def balanced(expression):
expression = list(expression.split())
try:
for i in expression:
if i == '(':
expression.insert(0, i)
elif i == ')':
expression.pop(0, i)
finally:
if len(expression) == 0:
return True
elif len(expression) > 0:
return False

print(balanced(input()))

Answer 1

expression.split() split the string at white spaces into a list: so list(expression.split()) is redundant...

also, roughly you are making a list of words (string), not a list of char... there is very few probabilities to get i==')' or i=='('...

try...finally must be used to handle errors... not to... what is your purpose by using them?

also, you seems to use the iterated expression as a stack to keep track of parenthesis... you must use another variable dedicated for that and not modify the original expression...

hint: to simply iterate over char of expression, don't split and/or list it, just do:

for chr in expression:

a string is basically a char list, and can be accessed as a char list in almost programming languages ^^

Answer 2

Thank you!