Reading-notes

scope

how variables and names are looked up in your code. It determines the visibility of a variable within the code.

The Python scope concept is generally presented using a rule known as the LEGB rule.

LEGB: Local, Enclosing, Global, and Built-in

1-What scopes are and how they work in Python

Python is a dynamically-typed language (variables in Python come into existence when you first assign them a value. On the other hand, functions and classes are available after you define them using def or class,)

Global scope: The names that you define in this scope are available to all your code.

Local scope: The names that you define in this scope are only available or visible to the code within the scope.

language that implements scope, there’s no way for you to access all the variables in a program at all locations in that program. In this case, your ability to access a given name will depend on where you’ve defined that name. like python

2-Why it’s important to know about Python scope

where you assign or define a name in your code determines the scope or visibility of that name.

** namespaces. These are the concrete mechanisms that Python uses to store names**

Names at the top level of a module are stored in the module’s namespace. __dict__

>>> sys.ps1
'>>> '
>>> sys.__dict__['ps1']
'>>> '

3-What the LEGB rule is and how Python uses it to resolve names

Local (or function) scope :

This Python scope contains the names that you define inside the function. These names will only be visible from the code of the function.

nonlocal names can be accessed from inside nested functions, but they can’t be modified or updated from there.
Enclosing(or nonlocal) scope special scope that only exists for nested functions
Global (or module) scope Names in this Python scope are visible from everywhere in your code.
Built-in scope ** Names in this Python scope are also available from everywhere in your code. **This scope contains names such as keywords, functions, exceptions,

4-How to modify the standard behavior of Python scope using global and nonlocal

Python provides two keywords that allow you to modify the content of global and nonlocal names. These two keywords are:

global
global counter # Declare counter as global
nonlocal The nonlocal statement consists of the nonlocal keyword followed by one or more names separated by commas
```
def nested(
   nonlocal var  # Declare var as nonlocal
  var += 100
```

a closure is an inner or nested function that carries information about its enclosing scope, even though this scope has completed its execution

Closures provide a way to retain state information between function calls

functools provides a function named partial() that makes use of the closure technique to create new function objects that can be called using predefined arguments.

 from functools import partial
>>> def power(exp, base):
...     return base ** exp
...
>>> square = partial(power, 2)
>>> square(10)

Bringing Names to Scope With import

import the modules or the names explicitly to your __main__ module

Discovering Unusual Python Scopes Comprehension Variables Scope:

A comprehension is a compact way to process all or part of the elements in a collection or sequence. You can use comprehensions to create lists, dictionaries, and sets.

Comprehensions consist of a pair of brackets ([]) or curly braces ({}) containing an expression, followed by one or more for clauses and then zero or one if clause per for clause.

Exception Variables Scope

The exception variable is a variable that holds a reference to the exception raised by a try statement. In Python 3.x, such variables are local to the except block and are forgotten when the block ends.

Class and Instance Attributes Scope

globals() In Python, globals() is a built-in function that returns a reference to the current global scope or namespace dictionary.
locals() This function updates and returns a dictionary that holds a copy of the current state of the local Python scope or namespace.
vars() vars() is a Python built-in function that returns the .dict attribute of a module, class, instance,
dir() You can use dir() without arguments to get the list of names in the current Python scope. If you call dir() with an argument