optimal if else statement for encapsulated dict

April 12, 2022

How to check if a dict has a key in an encapsulated dict and have the same else statement.

Basically how to optimize the following code, am assuming there must be a better way?

if "key_1" in my_dict:
    if "key_2" in my_dict["key_1"]:
        func_1()
    else:
        func_2()
else:
    func_2()

Of-course you cannot do the following cause if key_1 is not in my_dict then it will throw an error

if "key_2" in my_dict["key_1"]:
    func_1()
else:
    func_2()

>Solution :

The simplest check is:

 if "key_2" in my_dict.get("key_1", ()):

where get never raises a KeyError; when the key is missing, it returns the default value provided, an empty tuple, which "key_2" will never be in (the choice of the empty tuple over the empty dict is a minor efficiency boost; Python would have to reconstruct the empty dict for each call, but it can reuse the singleton tuple over and over without building new ones).

While it’s more verbose, the other approach to this is the EAFP approach; lookup the values assuming they exist, if you end up receiving a KeyError, it means one was missing:

try:
    my_dict["key_1"]["key_2"]  # If the value will be needed, assign to name here, use name in else:
except KeyError:
    func_2()  # One of the lookups failed, call func_2
else:
    func_1()  # Lookup succeeded, both keys exist, call func_1

Obviously:

if "key_1" in my_dict and "key_2" in my_dict["key_1"]:
    func_1()
else:
    func_2()

is also an option, but it requires looking up "key_1" twice, and is relatively verbose (that said, it is straightforward; it’s not an awful solution, I just enjoy being needlessly clever).