This content originally appeared on DEV Community and was authored by Super Kai (Kazuya Ito)
*Memos:
- My post explains global and nonlocal with 3 functions.
- My post explains global and nonlocal with 3 classes and 3 functions.
- My post explains a variable assignment.
First of all, there are 4 kinds of variables from the viewpoint of third() using 3 classes and 3 functions as shown below:
- A global variable is the variable out of any functions and classes.
- A non-local variable is the variable within outer functions.
- A local variable is the variable which is within its function.
- A class variable is the variable within its class.
""" It's from the viewpoint of `third()` """
num = 2 # <- Global variable
print(num) # 2
class Cls1:
num = 3 # <- Class variable
print(num) # 3
def first(self):
num = 4 # <- Non-local variable
print(num) # 4
class Cls2:
num = 5 # <- Class variable
print(num) # 5
def second(self):
num = 6 # <- Non-local variable
print(num) # 6
class Cls3:
num = 7 # <- Class variable
print(num) # 7
def third(self):
num = 8 # <- Local variable
print(num) # 8
Cls3().third()
Cls2().second()
Cls1().first()
A global statement can refer to a global variable as shown below. *The doc explains the rules for local and global variables in Python:
<Read>:
""" It's from the viewpoint of `third()` """
num = 2 # <- 〇
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- ✖
class Cls3:
num = 7 # <- ✖
def third(self):
global num # Here
print(num) # 2
Cls3().third()
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
# num = 2 # <- Commented
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- ✖
class Cls3:
num = 7 # <- ✖
def third(self):
global num # NameError: name 'num' is not defined.
print(num) # Did you mean: 'self.num'?
Cls3().third()
Cls2().second()
Cls1().first()
<Change>:
""" It's from the viewpoint of `third()` """
num = 2 # <- 〇
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- ✖
class Cls3:
num = 7 # <- ✖
def third(self):
global num # Here
num += 10 # Here
print(num) # 12
Cls3().third()
Cls2().second()
Cls1().first()
print(num) # 12
""" It's from the viewpoint of `third()` """
# num = 2 # <- Commented
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- ✖
class Cls3:
num = 7 # <- ✖
def third(self):
global num # NameError: name 'num' is not defined.
num += 10 # Did you mean: 'self.num'?
print(num)
Cls3().third()
Cls2().second()
Cls1().first()
print(num)
A nonlocal statement can refer to a non-local variable as shown below:
<Read>:
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- 〇
class Cls3:
num = 7 # <- ✖
def third(self):
nonlocal num # Here
print(num) # 6
Cls3().third()
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- 〇
class Cls2:
num = 5 # <- ✖
def second(self):
# num = 6 # <- Commented
class Cls3:
num = 7 # <- ✖
def third(self):
nonlocal num # Here
print(num) # 4
Cls3().third()
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
# num = 4 # <- Commented
class Cls2:
num = 5 # <- ✖
def second(self):
# num = 6 # <- Commented
class Cls3:
num = 7 # <- ✖
def third(self):
nonlocal num # SyntaxError: no binding
print(num) # for nonlocal 'num' found
Cls3().third()
Cls2().second()
Cls1().first()
<Change>:
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- 〇
class Cls3:
num = 7 # <- ✖
def third(self):
nonlocal num # Here
num += 10 # Here
print(num) # 16
Cls3().third()
print(num) # 16
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- 〇
class Cls2:
num = 5 # <- ✖
def second(self):
# num = 6 # <- Commented
class Cls3:
num = 7 # <- ✖
def third(self):
nonlocal num # Here
num += 10 # Here
print(num) # 14
Cls3().third()
Cls2().second()
print(num) # 14
Cls1().first()
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
# num = 4 # <- Commented
class Cls2:
num = 5 # <- ✖
def second(self):
# num = 6 # <- Commented
class Cls3:
num = 7 # <- ✖
def third(self):
nonlocal num # SyntaxError: no binding
num += 10 # for nonlocal 'num' found
print(num)
Cls3().third()
Cls2().second()
print(num)
Cls1().first()
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>:
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- 〇
class Cls3:
num = 7 # <- ✖
def third(self):
print(num) # 6
Cls3().third()
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- 〇
class Cls2:
num = 5 # <- ✖
def second(self):
# num = 6 # <- Commented
class Cls3:
num = 7 # <- ✖
def third(self):
print(num) # 4
Cls3().third()
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
num = 2 # <- 〇
class Cls1:
num = 3 # <- ✖
def first(self):
# num = 4 # <- Commented
class Cls2:
num = 5 # <- ✖
def second(self):
# num = 6 # <- Commented
class Cls3:
num = 7 # <- ✖
def third(self):
print(num) # 2
Cls3().third()
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
# num = 2 # <- Commented
class Cls1:
num = 3 # <- ✖
def first(self):
# num = 4 # <- Commented
class Cls2:
num = 5 # <- ✖
def second(self):
# num = 6 # <- Commented
class Cls3:
num = 7 # <- ✖
def third(self):
print(num) # NameError: name 'num' is not defined.
Cls3().third() # Did you mean: 'self.num'?
Cls2().second()
Cls1().first()
<Change>:
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- ✖
class Cls3:
num = 7 # <- ✖
def third(self):
num += 10 # UnboundLocalError: cannot access
print(num) # local variable 'num' where it is
Cls3().third() # not associated with a value
Cls2().second()
Cls1().first()
Using both a global and nonlocal statement in the same function gets error as shown below:
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- ✖
class Cls3:
num = 7 # <- ✖
def third(self):
global num # SyntaxError: name 'num'
nonlocal num # is nonlocal and global
print(num)
Cls3().third()
Cls2().second()
Cls1().first()
""" It's from the viewpoint of `third()` """
num = 2 # <- ✖
class Cls1:
num = 3 # <- ✖
def first(self):
num = 4 # <- ✖
class Cls2:
num = 5 # <- ✖
def second(self):
num = 6 # <- ✖
class Cls3:
num = 7 # <- ✖
def third(self):
nonlocal num # SyntaxError: name 'num'
global num # is nonlocal and global
print(num)
Cls3().third()
Cls2().second()
Cls1().first()
This content originally appeared on DEV Community and was authored by Super Kai (Kazuya Ito)