How to Determine Size of List in Python

Python provides the list in order to store multiple items in a single variable. The list is a dynamic strucuter which can contain multiple items in different counts and type. In this tutorial we try to determine the size of the list in different ways. Here are 10 examples to determine the size of a list in Python:

1. Using len() function: The defacto and most used way to determine the size of the is using len() function. The list is provided as paramter to the len() function and the size of the provided list is return as integer.

   my_list = [1, 2, 3, 4, 5]
   size = len(my_list)
   print(size)  # Output: 5
   

2. Using a loop (manual count): Python provides the for loop which can be used to iterate over items in a list. We can manually count the items in a list by iterating over them and increase the counter.

   my_list = [1, 2, 3, 4, 5]
   count = 0
   for _ in my_list:
       count += 1
   print(count)  # Output: 5
   

3. Using list comprehension with len(): Some lists may contains another list as items. These lists are called as nested lists. We can use the len() method and list comprehension in order to count a nested lists all items.

   my_list = [1, 2, 3, 4, 5]
   size = len([x for x in my_list])
   print(size)  # Output: 5
   

4. Using sum() with a generator expression: We can use the sum() method with generator expression by iterating over all list items and sum with 1 with every item which will return size of the list.

   my_list = [1, 2, 3, 4, 5]
   size = sum(1 for _ in my_list)
   print(size)  # Output: 5
   

5. Using recursion:

   def list_size(lst):
       if not lst:
           return 0
       return 1 + list_size(lst[1:])
   
   my_list = [1, 2, 3, 4, 5]
   size = list_size(my_list)
   print(size)  # Output: 5
   

6. Using reduce() from functools: We can use the reduce() and functools() methods in order to count list items and decide size of the list.

   from functools import reduce
   
   my_list = [1, 2, 3, 4, 5]
   size = reduce(lambda count, _: count + 1, my_list, 0)
   print(size)  # Output: 5
   

7. Using a while loop with an iterator: We can determine the size of the loop with the while loop by counting all items one by one.

   my_list = [1, 2, 3, 4, 5]
   it = iter(my_list)
   count = 0
   while True:
       try:
           next(it)
           count += 1
       except StopIteration:
           break
   print(count)  # Output: 5
   

8. Using map() with len(): Another usefull way is using the map() and len() methods like below.

   my_list = [1, 2, 3, 4, 5]
   size = len(list(map(lambda x: x, my_list)))
   print(size)  # Output: 5
   

9. Using numpy (for numerical lists): The 3rd party library numpy also provides the method named size we can simply determine the size of the list by providing the list to the numpy.size() method as parameter.

   import numpy as np
   
   my_list = [1, 2, 3, 4, 5]
   size = np.size(my_list)
   print(size)  # Output: 5
   

These examples show different ways to determine the size of a list in Python, using both built-in functions and more custom approaches.