How can I add new keys to a dictionary?

Added details: Update one or more keys

You can use the update() function to amend an existing key or even add one more:

dict.update({'d': 4})  # 'd' key is now part of our cool gang
print(dict)  # Outputs: {'a': 1, 'b': 2, 'c': 3, 'd': 4}
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Adding multiple values and other dictionary operations

Multiplicity & dictionary merges

# Adding multiple key-value pairs:
dict.update(e=5, f=6)  # Inviting 'e' and 'f' to join our hangout
print(dict)  # Outputs: {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5, 'f': 6}

# Merging two dictionaries (Python 3.9+):
another_dict = {'g': 7, 'h': 8}  # Meet our new friends 'g' and 'h'
dict |= another_dict  # Boom and they merged!
print(dict)  # Outputs: {'a': 1, 'b': 2, .... , 'g': 7, 'h': 8}
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Keep in mind: Starting Python 3.9, you can be neater by using dict1 |= dict2 instead of heavy-lifting with dict1.update(dict2).

Overwriting: There can only be one

If you think a key is a Highlander, think again. A key in a dictionary is unique. Assigning a value to an already existing key merely replaces the original.

dict['a'] = 'new value'  # 'a' decided to reinvent itself
print(dict['a'])  # Outputs: 'new value'
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Removing keys: Goodbye my lover, goodbye my friend

To rid a key and its linked value, banish it with either the del keyword or pop() method's wand:

del dict['f']  # Farewell 'f', you will be missed
value = dict.pop('c', None)  # 'c' left us but also left a void, hence default None
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More, more, more: Additional tools for your Python toolbox

Verifying a key's existence: I see dead people

Before meddling with keys, ensure they exist:

exists = 'key' in dict  # If it does, you will know
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Going through keys and values: Roll call!

To have an eagle's view of your dictionary contents, embark on an iteration adventure:

for key, value in dict.items():  # Let's take a roll call, shall we?
    print(f'{key}: {value}')
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Assembling dictionaries from sequences: Assemble!

If you have two lists, one hustling keys and the other bamboozling with corresponding values, join them with the power of zip:

keys = ['i', 'j']
values = [9, 10]
paired_dict = dict(zip(keys, values))  # Union of keys and values, assemble!
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Spring cleaning: Empty the dictionary

Feel the need for a fresh start? Don't worry, wipe the slate clean:

dict.clear()  # Henceforth, a clean slate is granted!
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Adding keys: Direct assignment for the win

Truth be told, direct assignment is much faster than update(). We all love things done in a jiffy, don't we?

# Fast
dict['k'] = 11  # Hustle done right

# Slower
dict.update({'k': 11})  # Like internet speed in the 90s
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