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Python Function

Nov 05, 20232 min read

parameters

  • 4. More Control Flow Tools — Python 3.12.0 documentation
  • 1. *args and **kwargs — Python Tips 0.1 documentation
  • Python argparse
  • \ Positional-Only Parameters
    • Positional-only parameters are placed before a / (forward-slash). The / is used to logically separate the positional-only parameters from the rest of the parameters.
  • * Keyword-Only Arguments
    • To mark parameters as keyword-only, indicating the parameters must be passed by keyword argument, place an * in the arguments list just before the first keyword-only parameter.
  •  **kwargs
    • special syntax used in function definitions to pass a keyworded, variable-length argument list.
>>> def pos_only_arg(arg, /):
...     print(arg)
...
>>> def kwd_only_arg(*, arg):
...     print(arg)
...
>>> def combined_example(pos_only, /, standard, *, kwd_only):
...     print(pos_only, standard, kwd_only)
 
>>> pos_only_arg(1)
1
 
>>> kwd_only_arg(arg=3)
3
 
>>> combined_example(1, 2, kwd_only=3)
1 2 3
 
>>> combined_example(1, standard=2, kwd_only=3)
1 2 3

Function Annotations

  • docs
    Annotations are stored in the __annotations__ attribute of the function as a dictionary and have no effect on any other part of the function. Parameter annotations are defined by a colon after the parameter name, followed by an expression evaluating to the value of the annotation. Return annotations are defined by a literal ->, followed by an expression, between the parameter list and the colon denoting the end of the def statement. The following example has a required argument, an optional argument, and the return value annotated:
>>> def f(ham: str, eggs: str = 'eggs') -> str:
...     print("Annotations:", f.__annotations__)
...     print("Arguments:", ham, eggs)
...     return ham + ' and ' + eggs
...
>>> f('spam')
Annotations: {'ham': <class 'str'>, 'return': <class 'str'>, 'eggs': <class 'str'>}
Arguments: spam eggs
'spam and eggs'

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