# Python – How to Convert List to Int

Lists are a common data structure in Python that can store multiple values. In some cases, you might need to convert the elements of a list from strings or other data types to integers for further processing.

In this article, we will explore different methods to convert a list to integers in Python. We will also discuss advanced techniques such as converting nested lists and handling errors and exceptions.

## 3 Methods for Converting List to Int

### Method 1: Using List Comprehension

List comprehension is a concise and efficient way to create a new list based on an existing one. Here’s an example of how to use list comprehension to convert a list of strings to integers:

``````list_of_strings = ['1', '2', '3', '4', '5']
list_of_integers = [int(i) for i in list_of_strings]
print(list_of_integers)
``````

### Method 2: Using the map() Function

The `map()` function applies a given function to each item in an iterable and returns a new iterable. In this case, we can use the `map()` function to apply the `int()` function to each element in the list:

``````list_of_strings = ['1', '2', '3', '4', '5']
list_of_integers = list(map(int, list_of_strings))
print(list_of_integers)
``````

### Method 3: Using a Loop

Another way to convert a list to integers is by using a loop. Here’s an example using a `for` loop:

``````list_of_strings = ['1', '2', '3', '4', '5']
list_of_integers = []

for i in list_of_strings:
list_of_integers.append(int(i))

print(list_of_integers)
``````

### Converting Nested Lists

In some cases, you might need to convert nested lists to integers. To do this, you first need to flatten the nested lists and then convert each element to an integer.

#### Flatten Nested Lists

Here’s a function that can be used to flatten nested lists:

``````def flatten_list(nested_list):
result = []
for item in nested_list:
if isinstance(item, list):
result.extend(flatten_list(item))
else:
result.append(item)
return result

nested_list = [['1', '2', '3'], ['4', '5', '6']]

flat_list = flatten_list(nested_list)
print(flat_list)
``````

#### Convert Nested Lists to Int

Now that we have a flattened list, we can convert each element to an integer using any of the previously discussed methods. Here‘s an example using list comprehension:

``````list_of_integers = [int(i) for i in flat_list]
print(list_of_integers)``````

### Handling Errors and Exceptions

When converting a list to integers, you might encounter elements that cannot be converted to integers, such as strings containing non-numeric characters. In such cases, you can use exception handling to skip the problematic elements or replace them with a default value.

Here’s an example using a `try` and `except` block to replace non-convertible elements with `None`:

``````list_with_non_numerics = ['1', '2', '3', 'four', '5']

def convert_to_int(element):
try:
return int(element)
except ValueError:
return None

list_of_integers = [convert_to_int(i) for i in list_with_non_numerics]
print(list_of_integers)
``````

## Use Cases and Applications

Converting lists to integers in Python can be useful in various situations, such as:

1. Data preprocessing in machine learning applications.
2. Manipulating and processing data from external sources, such as databases, files, or APIs.
3. Performing arithmetic operations on list elements.
4. Filtering or sorting lists based on numeric criteria.

## Conclusion

In this article, we covered different methods for converting a list to integers in Python, including list comprehension, the `map()` function, and loops. We also discussed advanced techniques for handling nested lists and error handling. By mastering these techniques, you can efficiently process and manipulate lists in Python for a wide range of applications.