reading-notes

Game of Greed 2

Source: Python Scope & the LEGB Rule: Resolving Names in Your Code

Scope

• Global - Avaliable to all code
• Local - Avaliable to other code within same scope (or nested within it)

LEGB Scope

• Local or Function – within a code block, function, or lambda. Only visibke within the function code.
• Enclosing or Nonlocal – Nested functions only. Scope of the outter function.
• Global - Top most scope in program, script or module.
• Build-in - Created when you run a script or session. Automatically loaded.

Modifying Scope

Keywords can be used to change the scope of a variable

Global

• When you try to assign a global name in a function, you create a new local name in the function scope
• global keyword can be used to modify behavior

>>> counter = 0  # A global name
>>> def update_counter():
...     counter = counter + 1  # Fail trying to update counter
...
>>> update_counter()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in update_counter
UnboundLocalError: local variable 'counter' referenced before assignment

>>> counter = 0  # A global name
>>> def update_counter():
...     global counter  # Declare counter as global
...     counter = counter + 1  # Successfully update the counter
...
>>> update_counter()
>>> counter
1

Generally bad practice. Instead, try using a local variable by passing the global in as an argument.

Nonlocal

• Similiar problem as above, but occurs in nested local scopes rather than global/local scope.
• Nonlocal names can’t be access from inner functions
• Modify them with nonlocal keyword

>>> def func():
...     var = 100  # A nonlocal variable
...     def nested():
...         nonlocal var  # Declare var as nonlocal
...         var += 100
...
...     nested()
...     print(var)
...
>>> func()
200