Is there a more efficient method to using Nested IF's in Python

Question

I want to find a way to make it more efficient to check whether an input is = to one number or another, but the only way i've learnt and can see is using nested if's in python.

def menu():
    while type(x) != int or x < 0 or x > 46:
        try:
            x = int(input("\nEnter a valid menu choice: "))
        except:
            print("\nInvalid input...\n")
    if x == 1:
        max1()
    elif x == 2:

    elif x == 3:

    elif x == 4:

This is my code design for a simple menu function to call upon other functions with a user's input, however i need 46 more if x == n.

Is there a faster way than doing an elif x == n+1 every line?

There are other options, such as a dispatch dict (constructed outside the function if you really need it to be efficient), but it seems to me like the 46-item menu might be a deeper problem. — user2357112
– user2357112, Commented Oct 28, 2016 at 19:32
The "best" solution depends on how different the menu items are from one another — Patrick Haugh
– Patrick Haugh, Commented Oct 28, 2016 at 19:32

kindall · Accepted Answer · 2016-10-28 20:30:18Z

2

Use a dictionary to hold the references to the functions, then use x to get the right function, then call it:

{1: max1, 2: whatever, 3: something_else}[x]()

In this case you're selecting the right function with an integer, so you could also use a list:

[max1, whatever, something_else][x-1]()

But I prefer the dictionary because it is easier to read: you can easily find the function associated with 13 if you need to change it.

N.B. there are no "nested ifs" in your code.

edited Oct 28, 2016 at 20:30

answered Oct 28, 2016 at 19:32

kindall

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Comments

Jared Goguen · Accepted Answer · 2016-10-28 19:32:34Z

1

Use a dictionary of integers to functions:

function_mapping = {
    1: max1,
    2: max2,
    ...
    n: maxn
}

function_mapping[x]()

If your functions are named this way, there are "hackish" ways of constructing this dictionary, e.g.

function_mapping = {i: globals()['max' + str(i)] for i in range(1,n+1)}

answered Oct 28, 2016 at 19:32

Jared Goguen

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Comments

ryachza · Accepted Answer · 2016-10-28 19:34:13Z

0

If none of these branches can be abstracted/combined, something like this could be useful:

def max1():
  pass # your block body

def error():
  pass # handle lookup failure

{1:max1
,2:...
}.get(x,error)()

Python dictionaries should be hashmaps so the lookup should be roughly constant time, especially for integer keys.

answered Oct 28, 2016 at 19:34

ryachza

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