What is best practice for instantiating a variable for use outside of a loop if you are only assigni-CodePudding

I frequently find myself in situations where I want to assign to a variable based upon the outcome of some comparison or other logic. I've done some Googling and I know that I CAN assign None to a variable and then assign to it later, but I just want to know if that's really the best way.

Here is an example of what I have in mind:

def function(v1, v2):
    least = None
    if v2 < v1:
        least = v2
    else:
        least = v1

Something in my mind is telling me there must be a better way, but I definitely wouldn't call myself an expert in Python.

CodePudding user response：

I wouldn't write the first assignment since it's immediately overwritten and the code's guaranteed to take one of the two branches.

def function(v1, v2):
    if v2 < v1:
        least = v2
    else:
        least = v1

You can shorten it to a one-liner if you like.

def function(v1, v2):
    least = v2 if v2 < v1 else v1

It's a matter of taste whether this is better or worse than the previous version. I like it, but it quickly becomes unreadable as the logic gets more complicated.

CodePudding user response：

There's no need to assign it first in your example, because all branches of the condition assign it.

Assigning a default value first is necessary if there could be code paths that don't assign the variable. A common situation is if you assign the variable in a loop; if the loop executes zero times, you won't set the variable.

def function(lst):
    result = None
    for item in lst:
        if somefunc(item):
            result = item
    return result

If you don't initialize result before the loop, you'll get an error if the list is empty or none of the elements satisfy the somefunc() condition.