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Python - Add Dictionary Items
Python Lists Access List Items ... Methods List Exercises Code Challenge Python Tuples · Python Tuples Access Tuples Update Tuples Unpack Tuples Loop Tuples Join Tuples Tuple Methods Tuple Exercises Code Challenge Python Sets · Python Sets Access Set Items Add Set Items Remove Set Items Loop Sets Join Sets Frozenset Set Methods Set Exercises Code Challenge Python Dictionaries...
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W3Schools
w3schools.com › python › python_dictionaries.asp
Python Dictionaries
List is a collection which is ordered and changeable. Allows duplicate members. Tuple is a collection which is ordered and unchangeable. Allows duplicate members. Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members. Dictionary is a collection which is ordered** and changeable. No duplicate members. *Set items are unchangeable, but you can remove and/or add items whenever you like. **As of Python version 3.7, dictionaries are ordered.
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W3Schools
w3schools.com › python › python_dictionaries_nested.asp
Python - Nested Dictionaries
Python Lists Access List Items ... Methods List Exercises Code Challenge Python Tuples · Python Tuples Access Tuples Update Tuples Unpack Tuples Loop Tuples Join Tuples Tuple Methods Tuple Exercises Code Challenge Python Sets · Python Sets Access Set Items Add Set Items Remove Set Items Loop Sets Join Sets Frozenset Set Methods Set Exercises Code Challenge Python Dictionaries...
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W3Schools
w3schools.com › python › gloss_python_dictionary_add_item.asp
Python Adding Items in a Dictionary
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W3Schools
w3schoolsua.github.io › python › python_dictionaries_add_en.html
Python Add Dictionary Items. Lessons for beginners. W3Schools in English
Python Add Dictionary Items. Update Dictionary. The update() method will update the dictionary with the items from a given argument. If the item does not exist, the item will be added. The argument must be a dictionary, or an iterable object with key:value pairs.
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GeeksforGeeks
geeksforgeeks.org › python › appending-a-dictionary-to-a-list-in-python
Appending a Dictionary to a List in Python - GeeksforGeeks
July 23, 2025 - Let's explore different ways in which we can append a dictionary to a list in Python. append() method is the most straightforward and simple way to append a dictionary to a list. ... a = [{'name': 'kate', 'age': 25}] b = {'name': 'Nikki', 'age': ...
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Python documentation
docs.python.org › 3 › tutorial › datastructures.html
5. Data Structures — Python 3.14.3 documentation
To avoid getting this error when trying to access a possibly non-existent key, use the get() method instead, which returns None (or a specified default value) if the key is not in the dictionary. Performing list(d) on a dictionary returns a list of all the keys used in the dictionary, in insertion order (if you want it sorted, just use sorted(d) instead).
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GeeksforGeeks
geeksforgeeks.org › python › python-ways-to-create-a-dictionary-of-lists
Ways to create a dictionary of Lists - Python - GeeksforGeeks
July 11, 2025 - defaultdict automatically creates a default value for keys that don’t exist, making it ideal for building a dictionary of lists dynamically. ... from collections import defaultdict # Initialize a defaultdict with list as the default type d = defaultdict(list) # Add values to the dictionary d[1].append("Apple") d[2].append("Banana") d[3].append("Carrot") print(d)
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W3Schools
w3schools.com › python › python_lists_add.asp
Python - Add List Items
Python Lists Access List Items ... Methods List Exercises Code Challenge Python Tuples · Python Tuples Access Tuples Update Tuples Unpack Tuples Loop Tuples Join Tuples Tuple Methods Tuple Exercises Code Challenge Python Sets · Python Sets Access Set Items Add Set Items Remove Set Items Loop Sets Join Sets Frozenset Set Methods Set Exercises Code Challenge Python Dictionaries...
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w3schools.com › python › python_lists.asp
Python Lists
Remove List Duplicates Reverse a String Add Two Numbers · Python Examples Python Compiler Python Exercises Python Quiz Python Challenges Python Server Python Syllabus Python Study Plan Python Interview Q&A Python Bootcamp Python Certificate Python Training ... Lists are used to store multiple items in a single variable. Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary...
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TutorialsPoint
tutorialspoint.com › adding-values-to-a-dictionary-of-list-using-python
Adding values to a Dictionary of List using Python
Use the append() method to add values to the lists by accessing them through their keys. And, then print the dictionary.
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W3Schools
w3schools.com › python › python_ref_dictionary.asp
Python Dictionary Methods
Remove List Duplicates Reverse a String Add Two Numbers · Python Examples Python Compiler Python Exercises Python Quiz Python Challenges Python Server Python Syllabus Python Study Plan Python Interview Q&A Python Bootcamp Python Certificate Python Training ... Python has a set of built-in methods that you can use on dictionaries. Learn more about dictionaries in our Python Dictionaries Tutorial. ... If you want to ...
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Python Examples
pythonexamples.org › python-list-of-dictionaries
Python List of Dictionaries
In this tutorial, we shall learn about List of Dictionaries in Python. How to create, access dictionaries in list, and then update or delete key:value pairs, or append dictionary to the list.
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Reddit
reddit.com › r/learnpython › how do you add a list as the value of a key inside a dictionary? what about tuples of lists?
r/learnpython on Reddit: How do you add a list as the value of a key inside a dictionary? What about tuples of lists?
April 3, 2022 -

I am trying to add a list, or a tuple of lists, as the value to a key inside a dictionary. I'm starting with a dictionary that has empty lists as values, and then adding to the value of each key inside a loop like this:

dict = {'key1': [], 'key2': [], 'key3': []}
list = ['a', 'b']
for key,value in dict.items():
#    dict[key].append(list)
    value.append(list)
print(dict)

What is the difference between dict[key].append(list) and value.append(list)? They both produce the same dictionary when the other is commented out.

Further, how would I add a second list to one of these values as a tuple? Something like adding the list ['c', 'd'] to key2, like this:

{'key1': [['a', 'b']], 'key2': [['a', 'b'], ['c', 'd']], 'key3': [['a', 'b']]}

Thanks for any replies!

Top answer
1 of 4
2
What is the difference between dict[key].append(list) and value.append(list)? They have the same result, yes, but the first is doing unnecessary work. The dict[key] part of the expression is fetching the value for the key, but you already have that in value, so just append to that. how would I add a second list to one of these values as a tuple? The value is a list, so just append whatever object you want. So if the object to append is a list just do: new_list = ['c', 'd'] for (key, value) ...: value.append(new_list) That's what you are already doing, so I'm not sure what your problem actually is.
2 of 4
2
You should do For key in dict.keys(): Dict[key].append(item). There’s no reason to keep track of the value if you’re unambiguously adding items to the list of each key. This is my opinion and I’m open to criticism but in my opinion that’s the most readable way to do it. Also apologies for mobile. I tried.
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TutorialsPoint
tutorialspoint.com › appending-a-dictionary-to-a-list-in-python
Appending a dictionary to a list in Python
In this article, we learned about lists, dictionaries with their syntax, and methods to append dictionaries to the list in python.
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Stack Overflow
stackoverflow.com › questions › 26367812 › appending-to-list-in-python-dictionary
Appending to list in Python dictionary - Stack Overflow
Top answer
1 of 3
252

list.append returns None, since it is an in-place operation and you are assigning it back to dates_dict[key]. So, the next time when you do dates_dict.get(key, []).append you are actually doing None.append. That is why it is failing. Instead, you can simply do

dates_dict.setdefault(key, []).append(date)

But, we have collections.defaultdict for this purpose only. You can do something like this

from collections import defaultdict
dates_dict = defaultdict(list)
for key, date in cur:
    dates_dict[key].append(date)

This will create a new list object, if the key is not found in the dictionary.

Note: Since the defaultdict will create a new list if the key is not found in the dictionary, this will have unintented side-effects. For example, if you simply want to retrieve a value for the key, which is not there, it will create a new list and return it.

2 of 3
40

Is there a more elegant way to write this code?

Use collections.defaultdict:

from collections import defaultdict

dates_dict = defaultdict(list)
for key, date in cur:
    dates_dict[key].append(date)
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W3Schools
w3schoolsua.github.io › python › python_lists_add_en.html
Python Add List Items. Lessons for beginners. W3Schools in English
Python - Add List Items. Append Items. Insert Items. Extend List. Add Any Iterable. Examples. Lessons for beginners. W3Schools in English
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W3Schools
w3schools.com › python › python_dictionaries_change.asp
Python - Change Dictionary Items
Python Lists Access List Items ... Methods List Exercises Code Challenge Python Tuples · Python Tuples Access Tuples Update Tuples Unpack Tuples Loop Tuples Join Tuples Tuple Methods Tuple Exercises Code Challenge Python Sets · Python Sets Access Set Items Add Set Items Remove Set Items Loop Sets Join Sets Frozenset Set Methods Set Exercises Code Challenge Python Dictionaries...
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DataCamp
datacamp.com › tutorial › python-dictionary-append
Python Dictionary Append: How to Add Key-Value Pairs | DataCamp
August 6, 2024 - In this example, we start with dictionary_w_list where the key 'fruits' maps to a list ['apple', 'banana']. By using the .append() method, we add 'cherry' to the list. This technique is particularly useful when managing collections of items within a single dictionary. Python 3.9 introduced the merge operator (|) for combining dictionaries.
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W3Schools
w3schools.com › python › python_lists_comprehension.asp
Python - List Comprehension
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