Can a variable be used inside a function without a Global declaration inside that function

CODE 1:

x=4    
def func():
          print("HELLO WORLD")
          y=x+2
          print (y)
          print (x) # gives o/p as HELLO WORLD 6,4,4.

func()    
print (x)

CODE 2:

x=4    
def func():

          print("HELLO WORLD")
          y=x+2
          x=x+2 # gives an error here
          print (y)
          print (x) 

func()
print (x)

开发者_运维知识库

In the first code, it is not showing any error, it's adding the x value to 2 and resulting back to y and it prints the o/p as 6,4,4. But Actually as I learnt so for, it should point an error because I am not giving the global declaration for x variable inside the func(). But its not ponting any error but in Code 2 it gives an error saying that x referenced before assignment.

The question is can x can be used for the assignment of its value to other variables? Even it is not followed with global declaration?

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You can read global variables without explicitly declaring them as global (Code 1)

But you are not allowed to assign to a global variable without explicitely declaring it as global. (Code 2)

This is because there is no harm in reading, but when assigning you might get unexpected behaviour (especially if it's a long code with many variables and you think it's a unique name you are using, but it's not).

---

In the first function you haven't assigned to x, so the compiler doesn't treat it as a local variable. The runtime will automatically get x from the containing scope. You can easily inspect that x is not considered a local variable:

>>> func1.__code__.co_varnames
('y',)

In the 2nd function you're assigning to x, so the compiler treats it as a local variable:

>>> func2.__code__.co_varnames
('x', 'y')

Hence the error you see: UnboundLocalError: local variable 'x' referenced before assignment.