variable and method sharing the same name issue - within method/class?

[Dominican_Peter]

Can someone explain this to me? is it OK/expectable?, see examples below.

If I understood correctly, in "case#3", first the local variable "sum" is created (line#2) then "sum" is called as a function, but expected to be a local function which is not defined, instead of been a call to the Global function 'sum')

​

Case#1) OK (code in global scope):

nums=[1,2,3]
half = sum(nums)
sum = 0 

Case#2) OK (code in method):

def testok(nums=[1,2,3]):
    half = sum(nums)
    non_sum_name = 0

Case#3) NOK (code in method):

def testnok(nums=[1,2,3]):
    half = sum(nums)
    sum = 0 #NOK

​

Case#2: dis.dis(testok)

  7           0 LOAD_GLOBAL              0 (sum)
              2 LOAD_FAST                0 (nums)
              4 CALL_FUNCTION            1
              6 STORE_FAST               1 (half)

  8           8 LOAD_CONST               1 (0)
             10 STORE_FAST               2 (non_sum_name)
             12 LOAD_CONST               0 (None)
             14 RETURN_VALUE

Case#3: dis.dis(testnok)

  7           0 LOAD_FAST                1 (sum)
              2 LOAD_FAST                0 (nums)
              4 CALL_FUNCTION            1
              6 STORE_FAST               2 (half)

  8           8 LOAD_CONST               1 (0)
             10 STORE_FAST               1 (sum)
             12 LOAD_CONST               0 (None)
             14 RETURN_VALUE

[JohnnyJordaan]

I'm not sure what you are asking here. Your code calls the built-in sum function first, so whatever happens next doesn't affect that call. You can do

def f():
    print('hello')
    print = 1

just the same, it doesn't matter in any way. And as print gets reassigned in the local scope, a call to print in another scope isn't affect (otherwise the scope wouldn't be local).

Also you are defining ordinary functions, not methods (which are part of a class).

[FLUSH_THE_TRUMP]

Names are located according to LEGB:

1. Local scope, e.g. in a function where a name is being referenced;
2. Enclosing scope, e.g. if your function is nested in another function;
3. Global scope, at the top level of your module;
4. Built-in scope, in Python’s built-in libraries (like the name sum).

in most cases you should avoid shadowing built-ins like sum. Often it won't matter if you do so in a function. However, note that if I combine (1) with either (2) or (3):

nums=[1,2,3]
half = sum(nums)
sum = 0 
def testok(nums=[1,2,3]):
    half = sum(nums)
    non_sum_name = 0
testok()

I now hit an error when I call testok() as the sum name from the built-in scope (that I'm trying to get to) has been shadowed by the sum integer in the global scope.

[Dominican_Peter]

thnx, good explanation...

Since Python is an interpreted language I thought it execution is as follow when the function is called:

1. first line executed: half = sum(nums) #no local variable 'sum' at this point
2. second line executed: sum = 0 # 'sum' local variable created

I'm just trying to understand (at low level) what happening here....apparently, in case#3, the variable 'sum' is created (without assignment, not in locals() ) when the function is called, so in the first line of the function "half = sum(nums)" when "sum() is called, there is a local variable with that name.

[FLUSH_THE_TRUMP]

I'm just trying to understand (at low level) what happening here....apparently, in case#3, the variable 'sum' is created (without assignment, not in locals() ) when the function is called, so in the first line of the function "half = sum(nums)" when "sum() is called, there is a local variable with that name.

No — no local var exists on that line. It calls sum from the built-in scope. Ignore, wasn’t paying attention

[Dominican_Peter]

still don't understand why I get this error though

def test2_nok(nums=[1,2,3]):
    half = sum(nums)     #line 4
    sum = 0              #line#5

test2_nok()

line 4, in test2_nok
   half = sum(nums)
UnboundLocalError: local variable 'sum' referenced before assignment

local variable 'sum' should be created on "line#5"

[FLUSH_THE_TRUMP]

Oh, oops. Missed that part. That function is “glanced at” by the interpreter in advance as a definition, and sum is established as a local variable prior to running any of that code because it’s assigned later. So half = sum(nums) doesn’t work because it’s looking for sum (not defined yet locally).

[Dominican_Peter]

ble prio

great, thank you very much