Re: Have do_nothing as default action for dictionary?

[Christopher Reimer via Python-list]

Greetings,

After reading everyone's comments and doing a little more research, I 
re-implemented my function as a callable class.


    def __call__(self, key, value):
    if key not in self._methods:
    return value
    return self._methods[key](value)

This behaves like my previous function, solved the problem that I had 
with the dictionary, the dictionary is created only once, a half dozen 
functions got moved into the new class, and the old class now has less 
clutter.


Thanks everyone!

Chris R.
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Re: Have do_nothing as default action for dictionary?

[Peter Otten]

Christopher Reimer via Python-list wrote:

> Greetings,
> 
> I was playing around this piece of example code (written from memory).
> 
> 
> def filter_text(key, value):
> 
>  def do_nothing(text): return text
> 
>  return {'this': call_this,
> 
>  'that': call_that,
> 
>  'what': do_nothing
> 
>  }[key](value)
> 
> 
> Is there a way to refactor the code to have the inner do_nothing
> function be the default action for the dictionary?


If it does nothing, why invoke it at all?

LOOKUP = {"this": call_this, ...}

def filter_text(key, value):
if key in LOOKUP:
return LOOKUP[key](value)
return value

If there are much more hits than misses:

def filter_text(key, value):
try:
process = return LOOKUP[key]
except KeyError:
return value
return process(value)

If you insist on invoking a noop func:

def do_nothing(text): return text

def filter_text(key, value):
return LOOKUP.get(key, do_nothing)(value)

With a collections.defaultdict (will grow to comprise new keys):

LOOKUP = defaultdict(LOOKUP, lambda: do_nothing)
def filter_key(key, value):
return LOOKUP[key](value)


> The original code was a series of if statements. The alternatives
> include using a lambda to replace the inner function or a try-except
> block on the dictionary to return value on KeyError exception.
> 
> What's the most pythonic and fastest?
> 
> Thank you,
> 
> Chris R.
> 


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Re: Have do_nothing as default action for dictionary?

[Peter Otten]

Christopher Reimer via Python-list wrote:

> Greetings,
> 
> I was playing around this piece of example code (written from memory).
> 
> 
> def filter_text(key, value):
> 
>  def do_nothing(text): return text
> 
>  return {'this': call_this,
> 
>  'that': call_that,
> 
>  'what': do_nothing
> 
>  }[key](value)
> 
> 
> Is there a way to refactor the code to have the inner do_nothing
> function be the default action for the dictionary?

If it does nothing, why invoke it at all?

LOOKUP = {"this": call_this, ...}
def filter_text(key, value):
 
> The original code was a series of if statements. The alternatives
> include using a lambda to replace the inner function or a try-except
> block on the dictionary to return value on KeyError exception.
> 
> What's the most pythonic and fastest?
> 
> Thank you,
> 
> Chris R.
> 


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Re: Have do_nothing as default action for dictionary?

[Chris Angelico]

On Mon, Sep 4, 2017 at 5:31 AM, Christopher Reimer via Python-list
 wrote:
> Greetings,
>
> I was playing around this piece of example code (written from memory).
>
>
> def filter_text(key, value):
>
> def do_nothing(text): return text
>
> return {'this': call_this,
>
>   'that': call_that,
>
>   'what': do_nothing
>
>  }[key](value)
>
>
> Is there a way to refactor the code to have the inner do_nothing function be
> the default action for the dictionary?

Easy: use the .get() method.

return {'this': call_this,

  'that': call_that,

 }.get(key, do_nothing)(value)

ChrisA
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Have do_nothing as default action for dictionary?

[Christopher Reimer via Python-list]

Greetings,

I was playing around this piece of example code (written from memory).


def filter_text(key, value):

    def do_nothing(text): return text

    return {'this': call_this,

  'that': call_that,

  'what': do_nothing

 }[key](value)


Is there a way to refactor the code to have the inner do_nothing 
function be the default action for the dictionary?


The original code was a series of if statements. The alternatives 
include using a lambda to replace the inner function or a try-except 
block on the dictionary to return value on KeyError exception.


What's the most pythonic and fastest?

Thank you,

Chris R.

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