A technique from a chatbot

[avi.e.gross at gmail.com]

I am a tad confused by a suggestion that any kind of GOTO variant is bad. The suggestion runs counter to the reality that underneath it all, compiled programs are chock full of GOTO variants even for simple things like IF-ELSE.

Consider the code here:

>> def first_word_beginning_with_e( list_ ):
>>      for word in list_:
>>          if word[ 0 ]== 'e': return word
>>      something_to_be_done_at_the_end_of_this_function()

If instead the function initialized a variable to nothing useful and in the loop if it found a word beginning with e and it still contained nothing useful, copied it into the variable and then allowed the code to complete the loop and finally returned the variable, that would simply be a much less efficient solution to the problem and gain NOTHING. There are many variants you can come up with and when the conditions are complex and many points of immediate return, fine, then it may be dangerous. But a single return is fine.

The function does have a flaw as it is not clear what it should do if nothing is found. Calling a silly long name does not necessarily return anything.

Others, like Thomas, have shown other variants including some longer and more complex ways.

A fairly simple one-liner version, not necessarily efficient, would be to just use a list comprehension that makes a new list of just the ones matching the pattern of starting with an 'e' and then returns the first entry or None. This shows the code and test it:

text = ["eastern", "Western", "easter"]

NorEaster = ["North", "West", "orient"]

def first_word_beginning_with_e( list_ ):
  return(result[0] if (result := [word for word in list_ if word[0].lower() == 'e']) else None)

print(first_word_beginning_with_e( text ))
print(first_word_beginning_with_e( NorEaster ))

Result of running it on a version of python ay least 3.8 so it supports the walrus operator:

eastern
None





-----Original Message-----
From: Python-list <python-list-bounces+avi.e.gross=gmail.com at python.org> On Behalf Of Thomas Passin via Python-list
Sent: Tuesday, April 2, 2024 3:31 PM
To: python-list at python.org
Subject: Re: A technique from a chatbot

On 4/2/2024 1:47 PM, Piergiorgio Sartor via Python-list wrote:
> On 02/04/2024 19.18, Stefan Ram wrote:
>>    Some people can't believe it when I say that chatbots improve
>>    my programming productivity. So, here's a technique I learned
>>    from a chatbot!
>>    It is a structured "break". "Break" still is a kind of jump,
>>    you know?
>>    So, what's a function to return the first word beginning with
>>    an "e" in a given list, like for example
>> [ 'delta', 'epsilon', 'zeta', 'eta', 'theta' ]
>>
>>    ? Well it's
>> def first_word_beginning_with_e( list_ ):
>>      for word in list_:
>>          if word[ 0 ]== 'e': return word
>>
>>    . "return" still can be considered a kind of "goto" statement.
>>    It can lead to errors:
>>
>> def first_word_beginning_with_e( list_ ):
>>      for word in list_:
>>          if word[ 0 ]== 'e': return word
>>      something_to_be_done_at_the_end_of_this_function()
>>    The call sometimes will not be executed here!
>>    So, "return" is similar to "break" in that regard.
>>    But in Python we can write:
>> def first_word_beginning_with_e( list_ ):
>>      return next( ( word for word in list_ if word[ 0 ]== 'e' ), None )
> 
> Doesn't look a smart advice.
> 
>>    . No jumps anymore, yet the loop is aborted on the first hit

It's worse than "not a smart advice". This code constructs an 
unnecessary tuple, then picks out its first element and returns that. 
The something_to_be_done() function may or may not be called.  And it's 
harder to read and understand than necessary.  Compare, for example, 
with this version:

def first_word_beginning_with_e(target, wordlist):
     result = ''
     for w in wordlist:
         if w.startswith(target):
             res = w
             break
     do_something_else()
     return result

If do_something_else() is supposed to fire only if the target is not 
found, then this slight modification will do:

def first_word_beginning_with_e(target, wordlist):
     result = ''
     for w in wordlist:
         if w.startswith(target):
             res = w
             break
     else:
         do_something_else()
     return result

[Using the "target" argument instead of "target[0]" will let you match 
an initial string instead of just a the first character].

> First of all, I fail to understand why there
> should be no jumps any more.
> It depends on how "return" and "if" are handled,
> I guess, in different context.
> Maybe they're just "masked".
> In any case, the "compiler" should have just
> done the same.
> 
>>    (if I guess correctly how its working).
> 
> Second, it is difficult to read, which is bad.
> The "guess" above is just evidence of that.
> 
> My personal opinion about these "chatbots", is
> that, while they might deliver clever solutions,
> they are not explaining *why* these solutions
> should be considered "clever".
> Which is the most important thing (the solution
> itself is _not_).
> 
> bye,
> 

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