Python update a key in dict if it doesn't exist

Methods to safely update a dictionary

Python 3.9+ merge operator

Got Python 3.9 or above? The merge operator (|) is your friend. It merges dictionaries and respects existing entries too.

my_dict = {'a': 1, 'b': 2}
new_entries = {'b': 3, 'c': 4}
my_dict = new_entries | my_dict  # 'b':2 says, "Nice try, but I was here first!"
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The art of dictionary unpacking

Dictionary unpacking (**) is like the all-you-can-eat buffet - it can handle multiple keys and defaults without even breaking a sweat.

defaults = {'a': 1, 'b': 2}
updated_dict = {**defaults, **my_dict}  # The dictionary buffet is now open!
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Conditional update using if

Ah, good ol' if. When you need to check before you insert, trust the if key not in d:.

if 'c' not in my_dict:
    my_dict['c'] = 3  # 'c' enters the chat
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Creative use of .get()

.get() can fetch a value without showing you the scary KeyError monster. But it also sets defaults. How? Check this out:

my_dict['d'] = my_dict.get('d', 4)  # 'd' either says "I'm already here!" or "Fine, let's go with 4."
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Handle your dict with care

Adjust for performance

The bigger your dict, the more you should consider dictionary unpacking or the merge operator – they're an athlete's dream, fast and efficient.

Python 3.9's features for clarity

Python 3.9's merge operator is not just about performance, it's also about code clarity – two birds, one stone.

Pythonic solutions for readability

Readability matters. Dictionary unpacking and setdefault method make your code more Pythonic and thus, more appeasing to human eyes.

Handling edge cases and special scenarios

Check before you step

Why trip over a dictionary key when you can see it coming with in and setdefault? These methods make your code more robust and intuitive.

Old Python, new tricks

Running on a pre-Python 3.9 version? You can still merge dicts and set defaults using dict.update() — don't let your Python version limit your creativity.

my_dict.update({k: defaults[k] for k in defaults if k not in my_dict})  # Yoohoo, Python 3.8 party!
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defaultdict for auto-defaults

Python's collections.defaultdict automatically assigns a default value for missing keys, whenever they're accessed. Isn't Python a sweetheart?

from collections import defaultdict

my_dict = defaultdict(lambda: 'default', my_dict)  # Missing key? No problemo!
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Making your dictionary updates go the distance

Readability—you're writing for humans

While code golfing may be fun for a while, it can sacrifice readability for brevity. And let's be honest, this ain't a typing speed contest.

Massive data? Embrace efficiency

Handling large datasets? Consider the runtime efficiency of these update methods. Remember, efficiency today might save you a headache tomorrow!

Future proof your code

Keeping up with Python's evolution means your dictionary manipulation skills will only get better. So stay sharp, stay updated!