Access the dictionary

Accessing Dictionary Items

You can access dictionary items by their keys. If you try to access a key that does not exist, you will get a KeyError exception.

Accessing a Key that Exists

You can access dictionary items by their keys. The following example accesses the key name of the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
print(dict1["name"])

Output:

command

C:\Users\username>python dict.py
John

In this example, we access the key name of the dictionary dict1. We then print the value of the key to the console. The output shows that the value of the key is John.

Danger

Accessing a Key that Does Not Exist

If you try to access a key that does not exist, you will get a KeyError exception. The following example accesses a key that does not exist:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
print(dict1["address"])

Output:

command

C:\Users\username>python dict.py
Traceback (most recent call last):
  File "dict.py", line 2, in <module>
    print(dict1["address"])
KeyError: 'address'

In this example, we try to access the key address of the dictionary dict1. We then print the value of the key to the console. The output shows that we get a KeyError exception because the key does not exist.

Accessing a Key using the get() Method

You can access dictionary items by their keys using the get() method. If you try to access a key that does not exist, you will get None. The following example accesses the key name of the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
print(dict1.get("name"))

Output:

command

C:\Users\username>python dict.py
John

In this example, we access the key name of the dictionary dict1. We then print the value of the key to the console. The output shows that the value of the key is John.

Accessing a Key that Does Not Exist using the get() Method

You can access dictionary items by their keys using the get() method. If you try to access a key that does not exist, you will get None. The following example accesses a key that does not exist:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
print(dict1.get("address"))

Output:

command

C:\Users\username>python dict.py
None

In this example, we try to access the key address of the dictionary dict1. We then print the value of the key to the console. The output shows that we get None because the key does not exist.

Length of a Dictionary

The length of a dictionary is the number of key-value pairs it contains. You can use the len() function to get the length of a dictionary. The following example gets the length of the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
print(len(dict1))

Output:

command

C:\Users\username>python dict.py
3

In this example, we get the length of the dictionary dict1. We then print the length of the dictionary to the console. The output shows that the length of the dictionary is 3.

Iterating Over a Dictionary

You can iterate over a dictionary using a for loop. When you iterate over a dictionary, you get the keys of the dictionary. The following example iterates over the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
for key in dict1:
    print(key + " => " + str(dict1[key]))

Output:

command

C:\Users\username>python dict.py
name => John
age => 30
city => New York

In this example, we iterate over the dictionary dict1. We then print the keys and values of the dictionary to the console. The output shows that we get the keys of the dictionary.

Accessing the Dictionary Items using the keys() Method

You can access the dictionary items using the keys() method. The following example accesses the dictionary items using the keys() method:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
for key in dict1.keys():
    print(key + " => " + str(dict1[key]))

Output:

command

C:\Users\username>python dict.py
name => John
age => 30
city => New York

In this example, we iterate over the dictionary dict1. We then print the keys and values of the dictionary to the console. The output shows that we get the keys of the dictionary.

Accessing the Dictionary Items using the values() Method

You can access the dictionary items using the values() method. The following example accesses the dictionary items using the values() method:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
for value in dict1.values():
    print(value)

Output:

command

C:\Users\username>python dict.py
John
30
New York

In this example, we iterate over the dictionary dict1. We then print the values of the dictionary to the console. The output shows that we get the values of the dictionary.

Accessing the Dictionary Items using the items() Method

You can access the dictionary items using the items() method. The following example accesses the dictionary items using the items() method:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
for key, value in dict1.items():
    print(key + " => " + str(value))

Output:

command

C:\Users\username>python dict.py
name => John
age => 30
city => New York

In this example, we iterate over the dictionary dict1. We then print the keys and values of the dictionary to the console. The output shows that we get the keys and values of the dictionary.

Checking if a Key Exists

You can check if a key exists in a dictionary using the in operator. The following example checks if the key name exists in the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
if "name" in dict1:
    print("The key 'name' exists in the dictionary")

Output:

command

C:\Users\username>python dict.py
The key 'name' exists in the dictionary

In this example, we check if the key name exists in the dictionary dict1. We then print a message to the console. The output shows that the key exists in the dictionary.

Checking if a Key Does Not Exist

You can check if a key does not exist in a dictionary using the not in operator. The following example checks if the key address does not exist in the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
if "address" not in dict1:
    print("The key 'address' does not exist in the dictionary")

Output:

command

C:\Users\username>python dict.py
The key 'address' does not exist in the dictionary

In this example, we check if the key address does not exist in the dictionary dict1. We then print a message to the console. The output shows that the key does not exist in the dictionary.

Checking if a Value Exists

You can check if a value exists in a dictionary using the in operator. The following example checks if the value John exists in the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
if "John" in dict1.values():
    print("The value 'John' exists in the dictionary")

Output:

command

C:\Users\username>python dict.py
The value 'John' exists in the dictionary

In this example, we check if the value John exists in the dictionary dict1. We then print a message to the console. The output shows that the value exists in the dictionary.

Checking if a Value Does Not Exist

You can check if a value does not exist in a dictionary using the not in operator. The following example checks if the value Jane does not exist in the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
if "Jane" not in dict1.values():
    print("The value 'Jane' does not exist in the dictionary")

Output:

command

C:\Users\username>python dict.py
The value 'Jane' does not exist in the dictionary

In this example, we check if the value Jane does not exist in the dictionary dict1. We then print a message to the console. The output shows that the value does not exist in the dictionary.

Checking if a Key Exists using the get() Method

You can check if a key exists in a dictionary using the get() method. The following example checks if the key name exists in the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
if dict1.get("name"):
    print("The key 'name' exists in the dictionary")

Output:

command

C:\Users\username>python dict.py
The key 'name' exists in the dictionary

In this example, we check if the key name exists in the dictionary dict1. We then print a message to the console. The output shows that the key exists in the dictionary.

Checking if a Key Does Not Exist using the get() Method

You can check if a key does not exist in a dictionary using the get() method. The following example checks if the key address does not exist in the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
if not dict1.get("address"):
    print("The key 'address' does not exist in the dictionary")

Output:

command

C:\Users\username>python dict.py
The key 'address' does not exist in the dictionary

In this example, we check if the key address does not exist in the dictionary dict1. We then print a message to the console. The output shows that the key does not exist in the dictionary.

Changing Dictionary Items

You can change the value of a dictionary item by using its key.

Changing a Key that Exists

You can change the value of a dictionary item by using its key. The following example changes the value of the key name of the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
dict1["name"] = "Jane"
print(dict1)

Output:

command

C:\Users\username>python dict.py
{'name': 'Jane', 'age': 30, 'city': 'New York'}

In this example, we change the value of the key name of the dictionary dict1. We then print the dictionary to the console. The output shows that the value of the key is changed to Jane.

Changing a Key that Does Not Exist

You can change the value of a dictionary item by using its key. The following example changes the value of the key address of the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
dict1["address"] = "London"
print(dict1)

Output:

command

C:\Users\username>python dict.py
{'name': 'John', 'age': 30, 'city': 'New York', 'address': 'London'}

In this example, we change the value of the key address of the dictionary dict1. We then print the dictionary to the console. The output shows that the value of the key is changed to London.

Changing a Key using the update() Method

You can change the value of a dictionary item by using its key. The following example changes the value of the key name of the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
dict1.update({"name": "Jane"})
print(dict1)

Output:

command

C:\Users\username>python dict.py
{'name': 'Jane', 'age': 30, 'city': 'New York'}

In this example, we change the value of the key name of the dictionary dict1. We then print the dictionary to the console. The output shows that the value of the key is changed to Jane.

Changing a Key that Does Not Exist using the update() Method

You can change the value of a dictionary item by using its key. The following example changes the value of the key address of the dictionary dict1:

dict.py

dict1 = {"name": "John", "age": 30, "city": "New York"}
dict1.update({"address": "London"})
print(dict1)

Output:

command

C:\Users\username>python dict.py
{'name': 'John', 'age': 30, 'city': 'New York', 'address': 'London'}

In this example, we change the value of the key address of the dictionary dict1. We then print the dictionary to the console. The output shows that the value of the key is changed to London.

Conclusion

In this tutorial, you have learned how to access the dictionary in Python. You also known as how to access the dictionary in Python using the key. You will also learn how to access the dictionary in Python using the get() method. You change the value of the dictionary in Python. For more tutorials, visit our Python Central Hub.

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diagram the three views, and which support set operations mermaid

  flowchart TD
  A["d.keys()"] --> B["dict_keys -- set-like"]
  C["d.items()"] --> D["dict_items -- set-like when the values are hashable"]
  E["d.values()"] --> F["dict_values -- NOT set-like"]
  B --> G["d.keys() & other  works"]
  D --> G
  F --> H["TypeError: unsupported operand type(s) for &"]
  I["all three are LIVE"] --> J["taken before a change, they show it afterwards"]
  J --> K["and mutating while iterating raises RuntimeError"]

keys, values and items are live windows on the dictionary rather than snapshots. Two of them behave like sets, because keys are unique and hashable -- which lets you intersect two dictionaries' keys directly. values cannot, because values may repeat and need not be hashable at all.

sketch Reading a key: four spellings, measured p5.js Pause Restart

Square brackets are the fastest because they are an operator rather than a method call, and they raise on a miss. get costs a method call and returns a default instead. The difference is around thirty nanoseconds, so choose by what should happen when the key is absent -- not by speed.

Check yourself

pch.quizTag pch.quizDefaultTitle

1. `d.keys() & {'a', 'z'}` works, but `d.values() & {1}` raises. Why?

   A values() is not iterable B Keys are unique and hashable, so the view is set-like; values may repeat and need not be hashable C values() is a generator D It is an oversight in the API
   pch.quizShowAnswer

   B — Keys are unique and hashable, so the view is set-like; values may repeat and need not be hashable — Verified: `TypeError: unsupported operand type(s) for &: 'dict_values'`. `items()` is set-like too, as long as the values happen to be hashable.

2. You take `ks = d.keys()` and then add a key. What does `list(ks)` show?

   A The keys as they were B The new key too — views are live C It raises D An empty list
   pch.quizShowAnswer

   B — The new key too — views are live — Views are windows, not snapshots. The related rule: mutating a dict while iterating it raises `RuntimeError: dictionary changed size during iteration`.

3. `d['a']` measured 112.6 ns and `d.get('a')` 145.1 ns. What should decide which you use?

   A Always the faster one B What should happen when the key is missing C Whether the dict is large D Whether the key is a string
   pch.quizShowAnswer

   B — What should happen when the key is missing — Thirty nanoseconds is a method call, not an algorithmic difference. `d[k]` raises — right when absence is a bug. `get` returns a default — right when absence is expected.

4. What is the risk of reaching for `.get()` everywhere?

   A It is slower B A genuinely missing key becomes a `None` that travels until it breaks something unrelated C It mutates the dict D It does not work with non-string keys
   pch.quizShowAnswer

   B — A genuinely missing key becomes a `None` that travels until it breaks something unrelated — `KeyError` names the missing key at the line that wanted it. A silent `None` surfaces later as a `TypeError` somewhere with no obvious connection to the real mistake.

Try it: Access Dictionary Exercises

Exercise 1 – get() Method

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Exercise 2 – Key Existence Check

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Exercise 3 – Nested Dictionary

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