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https://github.com/jsbueno/stackfull

Stack expression utility functions for Python
https://github.com/jsbueno/stackfull

Last synced: 30 days ago
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Stack expression utility functions for Python

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README 

        
PYTHON STACKFULL

================



This small utility package provides functions to be used

inside Python expressions that provide functionality

like that available in stack-based languages

(such as forth and postscript).



It registers a hidden variable in the current

running frame, which is a plain Python list -

calls to plain "push, pop, dup, retr", etc...

will just push/recover elements from that list.



The intent is that whenever in an expression

a value is complicated to retrieve - (or 

computationally extensive) - instead of

having to retrieve it in a previous line

and storing said value in a variable,

one gets the ability to "push" the value

in this implicit stack - and retrieve it

in another part of the same expression::

     

     `result = pop().upper() if not push(get_my+expensive_value()).isdigit() else pop()`



For convenience, most functions return the valued passed

to them in the first place (like the push above).



Compatibility

==============

As of version 0.20, and introduction of the `window`

function, stackfull is no longer Python 2.x compatible.



Available functions:

====================



clear

_____



    Clears the stack



cleartomark

___________



    Clears the stack up to the special sentinel value

    MARK - this allows for clean-up of the stack after

    a block of code, preserving the older values.

    If the stack is not empty, returns the last value on the

    stack non destructively, else, MARK itself is returned.



discard_if_false

________________



    Removes the last value in the stack if the expression is false.

    Made to be used in comprehensions, in the if part:



    Ex.:

    [pop().name for image in values if pop_if_false(push(image) is not None)]



dup

___



    Dplicates the last value on the stack

    It also returns the value duplicated in a non-destructive way



pop

___



    Pops the last value from the stack



popclear

________



    Pops the last value from the stack, and clears the stack.

    This allows stackfull to be used inside generator expressions

    and comprehensions, using a 'push' in the filtering expression,

    and 'popclear' on the result expression.



push

____



    Pushes a value into the stack, and returns the value itself

    Along with 'pop' and 'popclear' this is the heart of

    stackfull - as it allows an expensive function to be used

    in a 'if' or 'while' test, and still have its value

    available to use inside the defined block - without

    the need of an explicit auxiliar variable



push_if_true

____________



    Returns the value itself, and Pushes a value into the stack, if it

    is truthy. Otherwise does not touch the stack.

    Nice to use inside  comprehensions

    in the "if" part: if the expession is not True, it is never pushed, and

    extraneous values don't pile up on the stack.



    Ex.:

    [pop().name for image in values if push_if_true(image)]



retr

____



    Peeks the last value on the stack without consuming it



roll

____



    Rolls the last 'items' values on the stack by

    'amount' positions, changing their order.

    Returns the value on the top of the stack after

    the changes in a non destructive way.



stack

_____



    Retrieves the stack as an ordinary Python list

    (which it actually is), allowing one to perform

    extra desired operations, such as 'len' or 'insert'



window

______



    Pre-populates a frame stack with the seed values,

    and then iterates over the iterable -



    This allows one to use the stack with initial values in a simple way

    in a generator-expression context - like



    `fib = [push(stack()[-2] + stack()[-1]) for i in window(range(2, 10), 1,1)]`