if let syntax in Python

Question

Coming from Swift I'm having a bit of a hard time working with .None type of Python. I have a few functions which might return None if the object I'm looking for is not found in the array.

Then I have to nest my code as follows:

varA = self.getVariableByName(Variables.varA) 
if varA is None: 
    varB = self.getVariableByName(Variables.varB)
    varC = self.getVariableByName(Variables.varC) 
    if varB is not None and varC is not None: 
        # Do something with varB and varC 

In Swift I used to be able to bind the variables in the if statement

let f = getVariableByName
if f(Variables.varA) == nil, let varB = f(Variables.varB), let varC = f(Variables.varC) {
    // Do something with varB and varC
}

What is a more 'pythonic' way of dealing with None?

Answer 1

you can use the ":=" operator:

if varB := getVariableByName(Variables.varB):
    pass

Answer 2

I believe the nicest way to handle this case is exception handling. E.g. make self.getVariableByName raise an Exception if the element is not found. Then you could do:

try:
    varA = self.getVariableByName(Variables.varA)
except RuntimeError:
    varB = self.getVariableByName(Variables.varB)
    varC = self.getVariableByName(Variables.varC)
    # do something with varB and varC

to get the equivalent of your Swift example.

If you cannot/do not want to change self.getVariableByName, the best you can do is:

f = self.getVariableByName
if f(Variables.varA):
    varB, varC = f(Variables.varB), f(Variables.varC)
    if not (varB is None or varC is None):
        # do something with varB and varC