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global_x_local.rst

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>>> def f1(a):
...     print(a)
...     print(b)
...
>>> f1(3)
3
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in f1
NameError: name 'b' is not defined
>>> b = 6
>>> f1(3)
3
6
>>> def f2(a):
...     print(a)
...     print(b)
...     b = 9
...
>>> f2(3)
3
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in f2
UnboundLocalError: local variable 'b' referenced before assignment

# tag::F1_DIS[] >>> from dis import dis >>> dis(f1)

2 0 LOAD_GLOBAL 0 (print) <1>
3 LOAD_FAST 0 (a) <2> 6 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 9 POP_TOP
3 10 LOAD_GLOBAL 0 (print)
13 LOAD_GLOBAL 1 (b) <3> 16 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 19 POP_TOP 20 LOAD_CONST 0 (None) 23 RETURN_VALUE

# end::F1_DIS[] # tag::F2_DIS[] >>> dis(f2)

2 0 LOAD_GLOBAL 0 (print)
3 LOAD_FAST 0 (a) 6 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 9 POP_TOP
3 10 LOAD_GLOBAL 0 (print)
13 LOAD_FAST 1 (b) <1> 16 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 19 POP_TOP
4 20 LOAD_CONST 1 (9)
23 STORE_FAST 1 (b) 26 LOAD_CONST 0 (None) 29 RETURN_VALUE

# end::F2_DIS[] >>> def f3(a): ... global b ... print(a) ... print(b) ... b = 9 ... >>> f3(3) 3 6 >>> b 9 # tag::F3_DIS[] >>> dis(f3)

3 0 LOAD_GLOBAL 0 (print)
3 LOAD_FAST 0 (a) 6 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 9 POP_TOP
4 10 LOAD_GLOBAL 0 (print)
13 LOAD_GLOBAL 1 (b) 16 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 19 POP_TOP
5 20 LOAD_CONST 1 (9)
23 STORE_GLOBAL 1 (b) 26 LOAD_CONST 0 (None) 29 RETURN_VALUE

# end::F3_DIS[]

>>> def f4(b):
...     def f5(a):
...         nonlocal b
...         print(a)
...         print(b)
...         b = 7
...     return f5
...
>>> f5 = f4(8)
>>> f5(2)
2
8
>>> b
9
>>> f5(3)
3
7????
>>> dis(f5)
  4           0 LOAD_GLOBAL              0 (print)
              3 LOAD_FAST                0 (a)
              6 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
              9 POP_TOP
5 10 LOAD_GLOBAL 0 (print)
13 LOAD_DEREF 0 (b) 16 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 19 POP_TOP
6 20 LOAD_CONST 1 (7)
23 STORE_DEREF 0 (b) 26 LOAD_CONST 0 (None) 29 RETURN_VALUE