Defaultdict Module in Python with Syntax and Examples

In this article, we’ll learn about a very special and vividly used module in python, the defaultdict() module.

Starting from basics, covering its syntax, parameters and advanced codes, we’ll cover it all. So let’s get started.

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Defaultdict Module in Python

Dictionary in Python is an unordered collection of mutable lists. It is generally used for the purpose in which data has to be kept fixed, and no changes are required.

The defaultdict module has the ability to hold and manipulate the codes better than any other module. It keeps a dictionary as its fixed elements always.

A dictionary contains the immutable values, which can only be reciprocated in the code for any further alignment.

Example of Defaultdict Module in Python

thisistech = {1: 'wow', 2: 'welcome'}  
print("thisisdict: ")  
print(thisistech) 
print(thisistech[1])

Output:

thisisdict:
{1: ‘wow’, 2: ‘welcome’}
wow
>>>

More in Python DefaultDict

Python Defaultdict primarily contains two parts, one mutable and other immutable.

If the mutable part is parsed it does not allow the immutable part to get executed and vice -versa.

Syntax:

defaultdict(default_factory)

Import defaultdict
from collections import defaultdict
# a coder can Create a defaultdict

Coders can create a defaultdict with the defaultdict() constructor in runtime.

Code:

enternumber= defaultdict(i)
checknumber[a] = 1
checknumber[w] = 2
print(checknumber[c])

Output:

error

Parameters of defaultdict module in Python

default_factory: This function acts as a factory as it stores multiple values in it at a particular runtime and also saves the same for future processing also.

Code:

from collections import defaultdict 
def thisistech(): 
    return "hello!user!"

d = defaultdict(thisistech) 
d["one"] = 8
d["two"] = 9
  
print(d["one"]) 
print(d["two"]) 

Output:

8
9

Inner Working of Python Defaultdict Module

Defaultdict adds parses values internally and displays the output.

Default_factory: It is a function returning the default value of the code to the user in such a way that it is mutable at any time.

Example of Python Defaultdict module:

from collections import defaultdict 
p = defaultdict(lambda: "thisistech") 
p["firstuser"] = 1
p["seconduser"] = 2 
print(p["firstuser"]) 
print(p["seconduser"]) 
print(p["firstuser"]) 

Output:

1
2
welcome

__missing__(): This function takes default_factory as an argument in its main code, checks for the error and displays the error if any. It stops its execution in the meantime.

Example of Python _missing_():

from collections import defaultdict        
p = defaultdict(lambda: "thisistech") 
p["userone"] = 300
p["usertwo"] = 350
print(p.__missing__('userone')) 
print(p.__missing__('usertwo')) 

Output:

thisistech
thisistech
>>>

Using List as default_factory

When a class list is passed in an empty dictionary it is parsed in such a way that a user finds it immutable and hence does not change its value.

Example of Using list as default_factory in Python:

from collections import defaultdict     
p = defaultdict(list)   
for number in range(3): 
    p[number].append(number)
      
print("the appended list is:") 
print(p) 

Output:

the appended list is:
defaultdict(<class ‘list’>, {0: [0], 1: [1], 2: [2]})
>>>

Using int as default_factory

When the int class is parsed, it always interprets it line by line thus making it a mutable value.

Example of using int as Default_factory

from collections import defaultdict
p= defaultdict(int) 
   
o= [1, 2, 3, 4, 2, 4, 1, 2] 
   

for usernumber in p: 
       
   p[usernumber] += 1
       
print(p) 

Output:

defaultdict(<class ‘int’>, {})
>>>

Using ‘int’ as a Default Factory: Int(integer) can also be used in the default factory. And this can be simply done by giving the input statement as an integer and merging the same with list.

Code:

n='thisistech'
mydict=defaultdict(int)
for numbers in n:
                mydict[i]+=1              
mydict

Output:

error
Method or AttributeDescription
.__copy__()Supports for copy.copy()
.default_factoryHolds the callable object
.__missing__() tBy default provides the missing value
.__getitem__()Called when can’t find key in the data

Parsing Animation tools of Defaultdict

1. Counter

It is a built in data structure that is useful to count the occurrence of a number of values for a code.

2. Deque

Deque is a list used for inserting and removing items from the code. It acts as an interpreter which modifies the values as useful and not in the code.

3. ChainMap

ChainMap generally mixes dictionaries together and processes them in a way their values get combined and then returns a list of dictionaries. It does this without any restriction on the numeric value of dictionaries parsed.

Conclusion

In this article, we saw what is Python defaultdict, how and when it is used, its attributes and parameters.

A table has been summed up regarding what we’ve discussed until now.

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