*Memo:
- My post explains global and nonlocal with 3 functions (1).
- My post explains global and nonlocal with 3 functions (2).
Without a global or nonlocal statement, the closest non-local variable or a global variable can be referred to in order as shown below:
<Read(Intuitive version)>:
""" It's from the viewpoint of `third()` """ num = 2 # <- ✖ def first(): num = 3 # <- ✖ def second(): num = 4 # <- 〇 def third(): print(num) # 4 third() second() first() """ It's from the viewpoint of `third()` """ num = 2 # <- ✖ def first(): num = 3 # <- 〇 def second(): # num = 4 # <- Commented def third(): print(num) # 3 third() second() first() """ It's from the viewpoint of `third()` """ num = 2 # <- 〇 def first(): # num = 3 # <- Commented def second(): # num = 4 # <- Commented def third(): print(num) # 2 third() second() first() """ It's from the viewpoint of `third()` """ # num = 2 # <- Commented def first(): # num = 3 # <- Commented def second(): # num = 4 # <- Commented def third(): print(num) # NameError: name 'num' is not defined. third() # Did you mean: 'sum'? second() first() <Read(Unintuitive version)>:
""" It's from the viewpoint of `third()` """ def first(): def second(): def third(): print(num) # 4 num = 4 # <- 〇 third() num = 3 # <- ✖ second() num = 2 # <- ✖ first() """ It's from the viewpoint of `third()` """ def first(): def second(): def third(): print(num) # 3 # num = 4 # <- Commented third() num = 3 # <- 〇 second() num = 2 # <- ✖ first() """ It's from the viewpoint of `third()` """ def first(): def second(): def third(): print(num) # 2 # num = 4 # <- Commented third() # num = 3 # <- Commented second() num = 2 # <- 〇 first() """ It's from the viewpoint of `third()` """ def first(): def second(): def third(): print(num) # NameError: name 'num' is not defined. # Did you mean: 'sum'? # num = 4 # <- Commented third() # num = 3 # <- Commented second() # num = 2 # <- Commented first() <Change(Intuitive version)>:
""" It's from the viewpoint of `third()` """ num = 2 # <- ✖ def first(): num = 3 # <- ✖ def second(): num = 4 # <- ✖ def third(): num += 10 # UnboundLocalError: cannot access local variable print(num) # 'num' where it is not associated with a value third() print(num) second() print(num) first() print(num) <Change(Unintuitive version)>:
""" It's from the viewpoint of `third()` """ def first(): def second(): def third(): num += 10 # UnboundLocalError: cannot access local variable print(num) # 'num' where it is not associated with a value num = 4 # <- ✖ third() print(num) num = 3 # <- ✖ second() print(num) num = 2 # <- ✖ first() print(num) Using both a global and nonlocal statement in the same function gets error as shown below:
<Intuitive version>:
""" It's from the viewpoint of `third()` """ num = 2 # <- ✖ def first(): num = 3 # <- ✖ def second(): num = 4 # <- ✖ def third(): global num # SyntaxError: name 'num' is nonlocal and global nonlocal num print(num) third() second() first() """ It's from the viewpoint of `third()` """ num = 2 # <- ✖ def first(): num = 3 # <- ✖ def second(): num = 4 # <- ✖ def third(): nonlocal num # SyntaxError: name 'num' is nonlocal and global global num print(num) third() second() first() <Unintuitive version>:
""" It's from the viewpoint of `third()` """ def first(): def second(): def third(): global num # SyntaxError: name 'num' is nonlocal and global nonlocal num print(num) num = 4 # <- ✖ third() num = 3 # <- ✖ second() num = 2 # <- ✖ first() """ It's from the viewpoint of `third()` """ def first(): def second(): def third(): nonlocal num # SyntaxError: name 'num' is nonlocal and global global num print(num) num = 4 # <- ✖ third() num = 3 # <- ✖ second() num = 2 # <- ✖ first() 
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