counter.lua

function newCounter()
    local i = 0
    return function()     -- anonymous function
       i = i + 1
       return i
    end
end
 
c1 = newCounter()
print(c1())  --> 1
print(c1())  --> 2

counter.py

def new_counter():
    i = [0]
    def nested():
        i[0] += 1
        return i[0]
    return nested

>>>c = new_counter()
>>>c()
1
>>>c()
2

er_counter.py

def new_counter():
    i = 0
    def nested():
        i += 1
        return i
    return nested

c = new_counter()
c()
---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
<ipython-input-3-1f2bdb17cf98> in <module>()
----> 1 c()

<ipython-input-1-6662aa87dc2a> in nested()
      2     i = 0
      3     def nested():
----> 4         i += 1
      5         return i
      6     return nested

UnboundLocalError: local variable 'i' referenced before assignment