12.5. Function Scope¶
12.5.1. Rationale¶
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
12.5.2. Values Leaking¶
Values defined in function does not leak out:
>>> def add(a, b=1):
... c = 0
>>>
>>>
>>> print(a)
Traceback (most recent call last):
NameError: name 'a' is not defined
>>> print(b)
Traceback (most recent call last):
NameError: name 'b' is not defined
>>> print(c)
Traceback (most recent call last):
NameError: name 'c' is not defined
>>>
>>> add(1)
>>>
>>> print(a)
Traceback (most recent call last):
NameError: name 'a' is not defined
>>> print(b)
Traceback (most recent call last):
NameError: name 'b' is not defined
>>> print(c)
Traceback (most recent call last):
NameError: name 'c' is not defined
12.5.3. Outer Scope¶
Functions has access to global values
>>> data = [1, 2, 3]
>>>
>>>
>>> def add():
... return sum(data)
>>>
>>>
>>> add()
6
>>> print(data)
[1, 2, 3]
12.5.4. Shadowing¶
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
>>> data = [1, 2, 3]
>>>
>>>
>>> def add():
... data = [10, 20, 30] # Shadows name 'data' from outer scope
... return sum(data)
>>>
>>>
>>> add()
60
>>> print(data)
[1, 2, 3]
12.5.5. Global¶
globalkeyword allows modification of global variableUsing
globalkeyword is considered as a bad practice
>>> data = [1, 2, 3]
>>>
>>>
>>> def add():
... global data
... data = [10, 20, 30]
... return sum(data)
>>>
>>>
>>> add()
60
>>> print(data)
[10, 20, 30]
12.5.6. Global Scope¶
>>> globals()
{'__name__': '__main__',
'__doc__': None,
'__package__': None,
'__loader__': <class '_frozen_importlib.BuiltinImporter'>,
'__spec__': None,
'__annotations__': {},
'__builtins__': <module 'builtins' (built-in)>}
>>> dir(globals()['__builtins__'])
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException',
'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning',
'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError',
'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning',
'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', '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', 'all', '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']
>>> 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'}
12.5.7. 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 echo():
... a = 1
... print(locals())
>>>
>>>
>>> echo()
{'a': 1}
>>> def echo(a, b=2):
... c = 3
... print(locals())
>>>
>>>
>>> echo(1)
{'a': 1, 'b': 2, 'c': 3}
12.5.8. Shadowing Global Scope¶
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'
To restore default behavior of input() function use:
>>> input = __builtins__['input']
12.5.9. 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
>>> isfunction(sumif)
True
>>> 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'),
]