Python coding style

Question

I have two code snippets which essentially do the same thing. Here are the two samples :

retval = count or num_element > 0

and

if count or num_element > 0 :
    retval = True
else:
    retval = False

Is there any specific reason the first option is preferred over the second? I know that people have their own choices. But I am curious to know if there are any performance or other implications. I feel second way is more readable.

I would argue that 2nd case is way more readable. It's just an opinion, but yes it is, but I find it made idiot-readable. I think anyone who can read the language should have no big problems with the 1st code. With the 1st form you get 4 to 1 compression in lines of code, and in case of more than 2-3 such tests in a row, I would rather like to read 5 lines of 1st example than 20 lines of if-elses. Maybe that was it, also it's less typing =). — luk32
– luk32, Commented May 11, 2014 at 21:41

Martijn Pieters · Accepted Answer · 2014-05-11 21:28:28Z

10

They are not essentially the same. If count is a true value (non-zero, or not an empty container, etc.) then the value of count is assigned in the first form. The second form always assigns a boolean.

Unless the statement is part of a tight high-iteration-count loop, performance shouldn't be an issue. Even if it is part of a loop, the difference will be minute.

What remains is a stylistic choice, but your second form is usually extremely redundant.

Whenever I see a if test: value = True, else: value = False statement, it is usually a sign that someone hasn't understood that the test itself is already returning a boolean or can be made into one.

If you need a true boolean value, use:

retval = bool(count) or num_element > 0

otherwise just stick with the first option.

edited May 11, 2014 at 21:28

answered May 11, 2014 at 21:23

Martijn Pieters

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4 Comments

Santanu C Over a year ago

@Martjin: My bad. I have not posted my question correctly. I have edited it. However, your answer was spot on for my incomplete question.

kqr Over a year ago

Wouldn't it be neater to say retval = bool(count or num_element > 0)?

Martijn Pieters Over a year ago

@kqr: only if num_element is a custom class that returns something other than a boolean from the __gt__ method would it a make difference here.

kqr Over a year ago

@MartijnPieters I understand it wouldn't make a difference in most cases, I'm just suggesting it as an improvement – in part due to what you're saying and in part because it follows the general pattern also represented in things like stuff = set([1, 2, 3] * 4) where the entire RHS is wrapped.

Amber · Accepted Answer · 2014-05-11 21:35:58Z

2

If you specifically wanted retval to wind up as either True or False (rather than possibly the value of count if that value is truthy), you could do the following:

retval = True if count else num_element > 0

edited May 11, 2014 at 21:35

answered May 11, 2014 at 21:30

Amber

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2 Comments

Rick Over a year ago

I could be wrong here but if count were to be a false value then retval would also be false, no matter what num_element was.

Amber Over a year ago

I misremembered the original expression and thought it was an and. Fixed now.

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