11.5. Function Scope¶
Values defined in function does not leak out
Functions has access to global values
Shadowing is when you define variable with name identical to the one from outer scope
Shadowing in a function is valid only in a function
After function return, the original value of a shadowed variable is restored
globalkeyword allows modification of global variableUsing
globalkeyword is considered as a bad practice
11.5.1. Values Leaking¶
Values defined in function does not leak out
>>> def login():
... username = 'mwatney'
... password = 'nasa'
>>>
>>>
>>> print(username)
Traceback (most recent call last):
NameError: name 'username' is not defined
>>>
>>> print(password)
Traceback (most recent call last):
NameError: name 'password' is not defined
>>>
>>>
>>> login()
>>>
>>> print(username)
Traceback (most recent call last):
NameError: name 'username' is not defined
>>>
>>> print(password)
Traceback (most recent call last):
NameError: name 'password' is not defined
11.5.2. Outer Scope¶
Functions has access to global values
>>> user = ('Mark', 'Watney')
>>>
>>>
>>> def login():
... print(user)
>>>
>>>
>>> print(user)
('Mark', 'Watney')
>>>
>>> login()
('Mark', 'Watney')
>>>
>>> print(user)
('Mark', 'Watney')
11.5.3. Shadowing¶
When variable in function has the same name as in outer scope
Shadowing in a function is valid only in a function
Shadowed variable will be deleted upon function return
After function return, the original value of a shadowed variable is restored
>>> user = ('Mark', 'Watney')
>>>
>>>
>>> def login():
... user = ('Melissa', 'Lewis') # Shadows name 'user' from outer scope
... print(user)
>>>
>>>
>>> print(user)
('Mark', 'Watney')
>>>
>>> login()
('Melissa', 'Lewis')
>>>
>>> print(user)
('Mark', 'Watney')
11.5.4. Global¶
globalkeyword allows modification of global variableUsing
globalkeyword is considered as a bad practice
>>> user = ('Mark', 'Watney')
>>>
>>>
>>> def login():
... global user
... user = ('Melissa', 'Lewis')
... print(user)
>>>
>>>
>>> print(user)
('Mark', 'Watney')
>>>
>>> login()
('Melissa', 'Lewis')
>>>
>>> print(user)
('Melissa', 'Lewis')
11.5.5. Global Scope¶
>>> globals()
{'__name__': '__main__',
'__doc__': None,
'__package__': None,
'__loader__': <class '_frozen_importlib.BuiltinImporter'>,
'__spec__': None,
'__annotations__': {},
'__builtins__': <module 'builtins' (built-in)>}
>>> firstname = 'Mark'
>>> lastname = 'Watney'
>>>
>>> globals()
{'__name__': '__main__',
'__doc__': None,
'__package__': None,
'__loader__': <class '_frozen_importlib.BuiltinImporter'>,
'__spec__': None,
'__annotations__': {},
'__builtins__': <module 'builtins' (built-in)>,
'firstname': 'Mark',
'lastname': 'Watney'}
>>> def login():
... pass
>>>
>>>
>>> globals()
{'__name__': '__main__',
'__doc__': None,
'__package__': None,
'__loader__': <class '_frozen_importlib.BuiltinImporter'>,
'__spec__': None,
'__annotations__': {},
'__builtins__': <module 'builtins' (built-in)>,
'login': <function __main__.login()>}
11.5.6. Local Scope¶
Variables defined inside function
Variables are not available from outside
If outside the function, will return the same as
globals()
>>> locals()
{'__name__': '__main__',
'__doc__': None,
'__package__': None,
'__loader__': <class '_frozen_importlib.BuiltinImporter'>,
'__spec__': None,
'__annotations__': {},
'__builtins__': <module 'builtins' (built-in)>}
>>> def login():
... username = 'mwatney'
... password = 'nasa'
... print(locals())
>>>
>>>
>>> login()
{'username': 'mwatney', 'password': 'nasa'}
If outside the function, will return the same as globals():
>>> locals() == globals()
True
>>>
>>> locals() is globals()
True
11.5.7. Shadowing Global Scope¶
Defining variable with the same name as in outer scope
Shadowed variable will be deleted upon function return
Shadowing of a global scope is used frequently in Mocks and Stubs. This way, we can simulate user input. Note that Mocks and Stubs will stay until the end of a program.
>>> def input(prompt):
... return 'Mark Watney'
>>>
>>>
>>> name = input('Type your name: ')
>>> name
'Mark Watney'
>>>
>>> age = input('Type your age: ')
>>> age
'Mark Watney'
>>> from unittest.mock import MagicMock
>>> input = MagicMock(side_effect=['Mark Watney', '44'])
>>>
>>>
>>> name = input('Type your name: ')
>>> name
'Mark Watney'
>>>
>>> age = input('Type your age: ')
>>> age
'44'
To restore default behavior of input() function use:
>>> from builtins import input
11.5.8. Builtins¶
>>> import builtins
>>>
>>> dir(builtins)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException',
'BaseExceptionGroup', 'BlockingIOError', 'BrokenPipeError', 'BufferError',
'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError',
'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError',
'DeprecationWarning', 'EOFError', 'Ellipsis', 'EncodingWarning',
'EnvironmentError', 'Exception', 'ExceptionGroup', 'False',
'FileExistsError', 'FileNotFoundError', 'FloatingPointError',
'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError',
'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError',
'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError',
'MemoryError', 'ModuleNotFoundError', 'NameError', 'None',
'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError',
'OverflowError', 'PendingDeprecationWarning', 'PermissionError',
'ProcessLookupError', 'RecursionError', 'ReferenceError',
'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopAsyncIteration',
'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError',
'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError',
'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError',
'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning',
'ValueError', 'Warning', 'ZeroDivisionError', '_', '__build_class__',
'__debug__', '__doc__', '__import__', '__loader__', '__name__',
'__package__', '__spec__', 'abs', 'aiter', 'all', 'anext', 'any', 'ascii',
'bin', 'bool', 'breakpoint', 'bytearray', 'bytes', 'callable', 'chr',
'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr',
'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter',
'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash',
'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter',
'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min',
'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property',
'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice',
'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars',
'zip']
11.5.9. Use Case - 0x01¶
Simulate user input (for test automation)
>>> from unittest.mock import MagicMock
>>> input = MagicMock(side_effect=['lastname'])
>>> firstname = 'Mark'
>>> lastname = 'Watney'
>>>
>>>
>>> varname = input('Type variable name: ') #input: 'lastname'
>>>
>>> globals()[varname]
'Watney'
11.5.10. Assignments¶
"""
* Assignment: Function Scope Global
* Required: yes
* Complexity: easy
* Lines of code: 5 lines
* Time: 8 min
English:
1. Define in global scope `SELECT: set[str]` with values:
`'setosa', 'versicolor'`
2. Define function `sumif(features, label)`
3. Function sums `features`, only when `label` is in `SELECT`
4. When `label` is not in `select` return `0` (zero)
5. Run doctests - all must succeed
Polish:
1. Zdefiniuj w przestrzeni globalnej `SELECT: set[str]` z wartościami:
`'setosa', 'versicolor'`
2. Zdefiniuj funkcję `sumif(features, label)`
3. Funkcja sumuje `features`, tylko gdy `label` jest w `SELECT`
4. Gdy `label` nie występuje w `select` zwróć `0` (zero)
5. Uruchom doctesty - wszystkie muszą się powieść
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from inspect import isfunction
>>> assert isfunction(sumif), \
'Object `sumif` must be a function'
>>> assert SELECT is not Ellipsis, \
'Assign result to variable: `SELECT`'
>>> assert type(SELECT) is set, \
'Variable `result` has invalid type, should be set'
>>> assert all(type(x) is str for x in SELECT), \
'All rows in `result` should be str'
>>> sum(sumif(X,y) for *X, y in DATA[1:])
49.1
"""
DATA = [
('Sepal length', 'Sepal width', 'Petal length', 'Petal width', 'Species'),
(5.8, 2.7, 5.1, 1.9, 'virginica'),
(5.1, 3.5, 1.4, 0.2, 'setosa'),
(5.7, 2.8, 4.1, 1.3, 'versicolor'),
(6.3, 2.9, 5.6, 1.8, 'virginica'),
(6.4, 3.2, 4.5, 1.5, 'versicolor'),
(4.7, 3.2, 1.3, 0.2, 'setosa'),
]