Ever needed a nested #Python defaultdict?
You can do it like this:
`defaultdict(lambda: Counter())`
Or using a different factory:
`defaultdict(lambda: defaultdict(list))`
🐍✨
You can do it like this:
`defaultdict(lambda: Counter())`
Or using a different factory:
`defaultdict(lambda: defaultdict(list))`
🐍✨
January 17, 2025 at 12:19 PM
Ever needed a nested #Python defaultdict?
You can do it like this:
`defaultdict(lambda: Counter())`
Or using a different factory:
`defaultdict(lambda: defaultdict(list))`
🐍✨
You can do it like this:
`defaultdict(lambda: Counter())`
Or using a different factory:
`defaultdict(lambda: defaultdict(list))`
🐍✨
hate that i have to type from collections import defaultdict every time i wanna use defaultdict it's crazy that there's like frozenset and memoryview imported by default but not defaultdict
September 3, 2025 at 7:51 PM
hate that i have to type from collections import defaultdict every time i wanna use defaultdict it's crazy that there's like frozenset and memoryview imported by default but not defaultdict
TIL: by default, Django template engine cannot loop over a Python defaultdict
defaultdict is a sub-class of dict that implements the __missing__ method i.e.: you can define a default value if a key doesn't exists
`default(list)` will insert an empty list if you try to access a missing key
defaultdict is a sub-class of dict that implements the __missing__ method i.e.: you can define a default value if a key doesn't exists
`default(list)` will insert an empty list if you try to access a missing key
November 25, 2024 at 10:02 PM
TIL: by default, Django template engine cannot loop over a Python defaultdict
defaultdict is a sub-class of dict that implements the __missing__ method i.e.: you can define a default value if a key doesn't exists
`default(list)` will insert an empty list if you try to access a missing key
defaultdict is a sub-class of dict that implements the __missing__ method i.e.: you can define a default value if a key doesn't exists
`default(list)` will insert an empty list if you try to access a missing key
I use it multiple times a day. It replaced `defaultdict(int)` for me which had replaced `setdefault`.
September 11, 2025 at 6:50 PM
I use it multiple times a day. It replaced `defaultdict(int)` for me which had replaced `setdefault`.
"What does defaultdict(float) mean in Matplotlib?" I'm glad you asked!
defaultdict(float) is a dictionary that automatically starts any new key at 0.0
#Python #PythonTips #100DaysofCode
defaultdict(float) is a dictionary that automatically starts any new key at 0.0
#Python #PythonTips #100DaysofCode
May 22, 2026 at 9:52 PM
"What does defaultdict(float) mean in Matplotlib?" I'm glad you asked!
defaultdict(float) is a dictionary that automatically starts any new key at 0.0
#Python #PythonTips #100DaysofCode
defaultdict(float) is a dictionary that automatically starts any new key at 0.0
#Python #PythonTips #100DaysofCode
![>>> from collections import defaultdict
>>> data = """Tim,ID
... Sara,BR
... Thelma,CN
... Chris,RU
... Fina,ID
... Juliana,SE
... Roberto,CN
... Mario,PL
... Paul,CN"""
>>> countries = defaultdict(list)
>>> for line in data.splitlines():
... name, country_code = line.split(',')
... countries[country_code].append(name)
...
>>> countries
defaultdict(<class 'list'>,
{'BR': ['Sara'], 'CN': ['Thelma', 'Roberto', 'Paul'],
'ID': ['Tim', 'Fina'], 'PL': ['Mario'],
'RU': ['Chris'], 'SE': ['Juliana']})](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:uay2bzai5qhnwqcqz7ivsvzg/bafkreig5cgqgctp4ujs33aiyshxisau422emvsd5kicewskr6dl5fyszzm)
I thought I learned all the data structures Python has to offer but there's a defaultdict
What I understand about how it operates differently from a dict is it safeguard against empty values that haven't exist.
Perhaps I'll have to use more defaultdict vs dict more often??
What I understand about how it operates differently from a dict is it safeguard against empty values that haven't exist.
Perhaps I'll have to use more defaultdict vs dict more often??
October 1, 2025 at 5:14 PM
I thought I learned all the data structures Python has to offer but there's a defaultdict
What I understand about how it operates differently from a dict is it safeguard against empty values that haven't exist.
Perhaps I'll have to use more defaultdict vs dict more often??
What I understand about how it operates differently from a dict is it safeguard against empty values that haven't exist.
Perhaps I'll have to use more defaultdict vs dict more often??
defaultdict of dictionaries
(sorry not sorry)
(sorry not sorry)
October 3, 2023 at 3:30 PM
defaultdict of dictionaries
(sorry not sorry)
(sorry not sorry)
Yep, literally do stuff like that every day. Huge chunks of glossary.digitaltolkien.com or projectamaze.com are generated with defaultdict(Counter) or defaultdict(lambda: defaultdict(Counter))
September 11, 2025 at 9:13 PM
Yep, literally do stuff like that every day. Huge chunks of glossary.digitaltolkien.com or projectamaze.com are generated with defaultdict(Counter) or defaultdict(lambda: defaultdict(Counter))
I just completed "Historian Hysteria" - Day 1 - Advent of Code 2024 #AdventOfCode in #julialang adventofcode.com/2024/day/1
![input = get_numbers.(readlines("1a.txt"))
input = reduce(hcat, input)'
# part 1
l = input[:, 1]
r = input[:, 2]
sum(abs.(sort(l) .- sort(r)))
# part 2
counts = DefaultDict(0, countmap(r))
reduce(+, [el * counts[el] for el ∈ l])](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:6ziky27uf6ylt7gaiilhztm6/bafkreicgguxf42iiyrlvry5ei3jqx564gezvocinpih36gtttra2qnppbe)
December 1, 2024 at 3:44 PM
I just completed "Historian Hysteria" - Day 1 - Advent of Code 2024 #AdventOfCode in #julialang adventofcode.com/2024/day/1
Want to create a dict of lists in #Python? You can use defaultdict:
from collections import defaultdict
places = defaultdict(list)
while True:
city, country = input('Place: ').split()
places[country].append(city) # list is guaranteed
print(places)
from collections import defaultdict
places = defaultdict(list)
while True:
city, country = input('Place: ').split()
places[country].append(city) # list is guaranteed
print(places)
July 3, 2026 at 3:30 PM
Want to create a dict of lists in #Python? You can use defaultdict:
from collections import defaultdict
places = defaultdict(list)
while True:
city, country = input('Place: ').split()
places[country].append(city) # list is guaranteed
print(places)
from collections import defaultdict
places = defaultdict(list)
while True:
city, country = input('Place: ').split()
places[country].append(city) # list is guaranteed
print(places)
In fairness, I’m not sure I’ve used a defaultdict anywhere other than for Advent of Code. 😂
December 2, 2025 at 1:56 PM
In fairness, I’m not sure I’ve used a defaultdict anywhere other than for Advent of Code. 😂
“The defaultdict is very handy, but I find that it's rarely useful enough that I feel the need to use it.”
Read more 👉 pym.dev/default-dict...
#Python
Read more 👉 pym.dev/default-dict...
#Python
https://pym.dev/default-dictionary-values/
pym.dev
August 3, 2026 at 6:16 PM
“The defaultdict is very handy, but I find that it's rarely useful enough that I feel the need to use it.”
Read more 👉 pym.dev/default-dict...
#Python
Read more 👉 pym.dev/default-dict...
#Python
🐍📰 Using the #Python defaultdict Type for Handling Missing Keys
Using the Python defaultdict Type for Handling Missing Keys
In this step-by-step tutorial, you'll learn how the Python defaultdict type works and how to use it for handling missing keys when you're working with dictionaries. You'll also learn how to use a defaultdict to solve problems like grouping or counting ...
realpython.com
May 18, 2025 at 3:00 PM
🐍📰 Using the #Python defaultdict Type for Handling Missing Keys
Claude is really spotty on evaluating coding interview practice questions 🫤
September 15, 2025 at 3:31 AM
Claude is really spotty on evaluating coding interview practice questions 🫤
Если бы мне не за что было ненавидеть #rust
сегодня я бы ненавидел его за мучения с github.com/pydantic/pyd...
сегодня я бы ненавидел его за мучения с github.com/pydantic/pyd...
Release v2.41.5 · pydantic/pydantic-core
What's Changed
Correct invalid serialization of date/datetime/time/timedelta by pulling downcast checks up by @astei in #1851
avoid getting default values from defaultdict by @davidhewitt in #1853...
github.com
December 4, 2025 at 8:21 PM
Если бы мне не за что было ненавидеть #rust
сегодня я бы ненавидел его за мучения с github.com/pydantic/pyd...
сегодня я бы ненавидел его за мучения с github.com/pydantic/pyd...
Really useful python features: check out collections.defaultdict to avoid KeyErrors: my_dict = defaultdict(list). #python #pythontips #programming
January 29, 2025 at 2:29 PM
Really useful python features: check out collections.defaultdict to avoid KeyErrors: my_dict = defaultdict(list). #python #pythontips #programming
When I don’t need the default value for inexistent keys, this is what I use instead of a defaultdict.
As for being faster, MAYBE dict is in C but defaultdict is implemented in Python. That could make a huge difference.
As for being faster, MAYBE dict is in C but defaultdict is implemented in Python. That could make a huge difference.
December 7, 2024 at 7:16 AM
When I don’t need the default value for inexistent keys, this is what I use instead of a defaultdict.
As for being faster, MAYBE dict is in C but defaultdict is implemented in Python. That could make a huge difference.
As for being faster, MAYBE dict is in C but defaultdict is implemented in Python. That could make a huge difference.
Pythonのdefaultdictでは参照しただけでも要素が増えるから、そのせいで実行速度もメモリも増えたりすることがある、
これはPythonですが少し話題に上がっていたので。
これはPythonですが少し話題に上がっていたので。
May 4, 2026 at 7:34 AM
Pythonのdefaultdictでは参照しただけでも要素が増えるから、そのせいで実行速度もメモリも増えたりすることがある、
これはPythonですが少し話題に上がっていたので。
これはPythonですが少し話題に上がっていたので。
Recently stumbled on this combo of two Python stdlib features (both in 'collections') that work well together to keep running partitioned counts (e.g. per-category or per-year):
c = defaultdict(Counter)
c[partition].update(list_of_stuff)
c = defaultdict(Counter)
c[partition].update(list_of_stuff)
March 14, 2024 at 12:58 AM
Recently stumbled on this combo of two Python stdlib features (both in 'collections') that work well together to keep running partitioned counts (e.g. per-category or per-year):
c = defaultdict(Counter)
c[partition].update(list_of_stuff)
c = defaultdict(Counter)
c[partition].update(list_of_stuff)
You can easily create a multi-dict in Python.
You can use `collections.defaultdict` and the built-in `list`.
This creates a dictionary that maps every single key to an empty list by default.
Then, appending to a key means adding a value to that key.
But this is “cheating”.
Why is it cheating..?
You can use `collections.defaultdict` and the built-in `list`.
This creates a dictionary that maps every single key to an empty list by default.
Then, appending to a key means adding a value to that key.
But this is “cheating”.
Why is it cheating..?
![Diagram showing how to create a multidict using `collections.defaultdict` and the built-in `list`.
Code:
from collections import defaultdict
multidict = defaultdict(list)
print(multidict["SW"]) # []
print(multidict["LotR"]) # []
multidict["SW"].append("Han Solo")
multidict["SW"].append("R2D2")
print(multidict["SW"]) # ['Han Solo', 'R2D2']](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:4642ovs4svxe3k3echdm4rks/bafkreib7lu2rv2orymudwr2a7rgik6p3mah524j2hsbacmghwywrsp3jxm)
April 20, 2025 at 11:04 AM
You can easily create a multi-dict in Python.
You can use `collections.defaultdict` and the built-in `list`.
This creates a dictionary that maps every single key to an empty list by default.
Then, appending to a key means adding a value to that key.
But this is “cheating”.
Why is it cheating..?
You can use `collections.defaultdict` and the built-in `list`.
This creates a dictionary that maps every single key to an empty list by default.
Then, appending to a key means adding a value to that key.
But this is “cheating”.
Why is it cheating..?
TIL: by default, Django template engine cannot loop over a Python defaultdict
defaultdict is a sub-class of dict that implements the __missing__ method i.e.: you can define a default value if a key doesn't exists
`default(list)` will insert an empty list if you try to access a missing key
defaultdict is a sub-class of dict that implements the __missing__ method i.e.: you can define a default value if a key doesn't exists
`default(list)` will insert an empty list if you try to access a missing key
November 25, 2024 at 10:56 PM