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Specify Argument Type For List of Dictionary For a Python

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  • Last Updated : 22 Apr, 2022

In this article, we will see how we can specify the argument type for a list of Dictionary for Python

As we know, Python is a dynamically typed language so the data type of a variable can change anytime. If a variable containing an integer may hold a string in the future, which can lead to Runtime Errors, Therefore knowing the data type of the arguments becomes important for a function. Here we will use a typing python module which help us to resolve this problem.

So, In general, we can write a function in Python as:


def add(a, b):
    return a+b

But here, we don’t know if the function ‘add’ accepts int or float values. PEP 3107 Function Annotations now enable us to write our code as:


def add(a: int, b: int) -> int:
    return a+b

Now we can easily tell by reading the code what is the expected data type of the parameters and output. 

So, now for Specifying Argument Type for List of Dictionary for a python function. It will be as simple as

Example 1:

Here we can see:

  • The datatype for arguments.
  • The type of output is a list that contains a Dictionary with values – a string and integer.


# typing is a standard library
from typing import List, Dict
def GetData(name: str, age: int) -> List[Dict[str, int]]:
    return [{'name': name, 'age': age}]
print(GetData('Sandeep Jain', 35))


[{'name': 'Sandeep Jain', 'age': 35}]

Example 2:

In this example, we are using list comprehension to get a List of Dictionary. 


# import library
from typing import List, Dict
# define function
def get_list_of_dicts(name: str, category: str) -> Dict[str, str]:
    return [{'name': name, 'category': category}]
Fruit = ["Mango", "tomato", "potato", "papaya"]
Fruit_type = ["fruit", "vegetable", "vegetable", "fruit"]
res = [get_list_of_dicts(Fruit[i], Fruit_type[i]) for i in range(3)]


[[{‘name’: ‘a’, ‘surname’: 1}], [{‘name’: ‘b’, ‘surname’: 2}], [{‘name’: ‘c’, ‘surname’: 3}]]

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