Python: Should I avoid initialization of variables inside blocks?

Question

Problem

I have a code like this

if condition:
    a = f(x)
else:
    a = g(y)

Initialization of a inside of the block looks bad for me. Can it be written better?

I cannot use ternary operator, because names of functions and/or lists of arguments are long. Saying "long" I mean that the following expression

a = f(x) if condition else g(y)

will take more than 79 (sometimes even more than 119) symbols with real names instead of a, f, g, x, y and condition. Usage of multiple slashes will make the code ugly and messy.

I don't want to initialize a with result of one of the functions by defaul, because both function are slow and I cannot allow such overhead

a = g(y)
if condition:
    a = f(x)

I can initialize the variable with None, but is this solution pretty enough?

a = None
if condition:
    a = f(x)
else:
    a = g(y)

Let me explain my position: in C and C++ variables inside of a block have the block as their scope. In ES6 the let keyword was introduced — it allows to create variables with the same scoping rules as variables in C and C++. Variables defined with old var keyword have similar scoping rules as in Python. That's why I think that initialization of variables should be made outside blocks if I want to use the variables outside these blocks.

Update

Here is more complicated example

for obj in gen:
    # do something with the `obj`
    if predicate(obj):
        try:
            result = f(obj)
        except Exception as e:
            log(e)
            continue
    else:
        result = g(obj)
    # do something useful with the `result`
else:
    result = h(obj)

display(result)

I go through elements of some generator gen, process them and perform some actions on the result on each iteration. Then I want to do something with the last result outside of the loop.

Is it pythonic enough to not assign a dummy value to the result beforehand? Doesn't this make the code less readable?

Question

Is it good to initialize variables inside if/else/for/etc. in Python?

Answer 1

Python has no block scope... the scope is the whole function and it's perfectly pythonic to write

if <condition>:
    a = f()
else:
    a = g()

If you want to write in C++ then write in C++ using C++, don't write C++ using Python... it's a bad idea.