max() give "int" not callable error in my function

Question

I have a problem using max() inside my function. When a create a list with integers, max function works good. However when a create a list in my function and then using max() with my integer list then it gives "TypeError: 'int' object is not callable" error.
Where am I wrong and how can I fix it?

>>> a = [1,2,3,4,5] # A simple list
>>> max(a) # It works fine
>>> 5
>>> def palen(num):
...     min = 10**(num-1)
...     max = (10**num)-1
...     a=[] # Another list
...     mul=0
...     for i in range(max,min-1,-1):
...         for j in range (max,min-1,-1):
...             mul=i*j
...             if str(mul)==str(mul)[::-1]:
...                 a.append(mul)
...     return max(a)
...
>>> palen(2)
Traceback (most recent call last):
 File "<input>", line 1, in <module>
 File "<input>", line 11, in palen
TypeError: 'int' object is not callable

Answer 1

Because you redefine max as a int number with

max = (10**num)-1

so you can not Call a number to help you get the max value of a list. Change the variable name will be ok:

def palen(num):
  min_num = 10**(num-1)
  max_num = (10**num)-1
  a=[] # Another list
  mul=0
  for i in range(max_num,min_num-1,-1):
    for j in range (max_num,min_num-1,-1):
      mul=i*j
      if str(mul)==str(mul)[::-1]:
        a.append(mul)
  return max(a)

print palen(2)

Answer 2

On line 6 of your readout you define a variable called max. This shadows the pointer to max(). This is why you can't use the max() function anymore. You need to rename your variable max on line 6 and everywhere else you use it to fix this.

For more information on namespaces in Python see this interesting page I just found: http://bytebaker.com/2008/07/30/python-namespaces/