Shrinking very large If statements in python

Question

I have a situation where I have 4 variables named eax,ebx,ecx and edx, and any one of them may be set to any of these vars: var1,var,var3 and var4, however they are set as the string "varx" instead of the value of varx, but only one of them will every need fixing at a time. I have been using this if statement:

  if eax=="var1":
    eax=var1
  elif ebx=="var1":
    ebx=var1
  elif ecx=="var1":
    ecx=var1
  elif edx=="var1":
    edx=var1
  elif eax=="var2":
    eax=var2
  elif ebx=="var2":
    ebx=var2
  elif ecx=="var2":
    ecx=var2
  elif edx=="var2":
    edx=var2
  elif eax=="var3":
    eax=var3
  elif ebx=="var3":
    ebx=var3
  elif ecx=="var3":
    ecx=var3
  elif edx=="var3":
    edx=var3
  elif eax=="var4":
    eax=var4
  elif ebx=="var4":
    ebx=var4
  elif ecx=="var4":
    ecx=var4
  elif edx=="var4":
    edx=var4

But I am aware that this is very bad practise. Is there a way for me to compact this if statement?

Thanks.

Answer 1

You could try thinking about the update process for a single variable at a time and create a function to handle that. Then the logic can be easily reused for each variable. This means you'll have a function that handles 4 (or 5) cases and call it 4 times (resulting in 8-9 steps) instead of having to do each combination (16 steps). This also has the benefit of making your code more readable and maintainable.

For example:

def get_var(x):
    if x == "var1":
        return var1
    if x == "var2":
        return var2
    if x == "var3":
        return var3
    if x == "var4":
        return var4
    return x

eax = get_var(eax)
ebx = get_var(ebx)
ecx = get_var(ecx)
edx = get_var(edx)

Note this is basically a switch statement (which is not supported by Python), and can instead be written in the following way (which can be easier to update depending on the rest of your code):

vars_lookup = {
    "var1": var1,
    "var2": var2,
    "var3": var3,
    "var4": var4,
}

def get_var(x):
    return vars_lookup.get(x, x)

eax = get_var(eax)
ebx = get_var(ebx)
ecx = get_var(ecx)
edx = get_var(edx)

Note here that the get method of the dict type works like the usual brackets notation (vars_lookup[x]), but handles cases where the key is not found in the dictionary and then returns the default value (the second argument).