Good code patterns in Python

[Max M]

Michael Chermside wrote:

> Will Stuyvesant writes:
> 
>>If you know that your source code is going to be used
>>later by others, then I feel that code with the pattern:
>>
>>    if some_condition:
>>        some_name = some_value
>>    else:
>>        some_name = other_value
>>
>>is often a mistake.  Much better, safer, would be:
>>
>>    some_name = some_value
>>    if not some_condition:
>>        some_name = other_value
> 
> I disagree with you... I think that the first form is superior
> to the second. Here are two reasons.
> 
> My number one reason is readability. Seeing "some_name = some_value"
> when some_name is ACTUALLY going to take on other_value is very
> misleading to the reader.


If a programmer has a hard time reading the first version, he really 
should have another job ;-)

You cannot expect to know from any program what value a variable has 
from a cursory glance.

And there are many times where it is the prefered idiom. Like:


result = []
if something:
     result.append(stuff)
if something_else:
     result.append(stuff)
return result


Another example:


url = self.url
http = 'http://'
if url[:len(http) != http
     url = http + url
return url


The "first" form is not an unusual pattern to see in programmes. And I 
prefer it myself, as it prevents small stupid mistakes better than the 
"second" form.

The first form frequently mutates into nested code like:


if some_condition:
     some_name = some_value
else:
     if some_exotic_condition:
         some_name = other_value


Where it can be pretty obscure what value a variable has, and if it is 
assigned one at all.

And you have to make shure to set the "default" value in all itterations 
of the code.


if some_condition:
     some_name = some_value
else:
     if some_exotic_condition:
         some_name = third_value
     else:
         some_name = other_value


It would have been a simpler and less error prone procedure to change 
the code if it it had used the first form.


some_name = other_value
if some_condition:
     some_name = some_value
else:
     if some_exotic_condition:
         some_name = third_value


regards Max M