Python Find in List

Given that it holds items of all datatypes as a collection, a Python list is a widely used container of items in Python. Therefore, understanding some list functions is required for everyday programming.

What do Python lists do?

Lists are among the strongest data structures and an inbuilt data type of Python. They serve storage spaces for numerous, frequently connected things under one unique variable.

Square brackets are used to surround and arrange items []. A comma (,) is used to distinguish each element within the square brackets.

Code

Output:

['Peter Parker', 35, 'New York', 3.45]

You can notice in the code above that lists can include items of different data types, demonstrating the heterogeneity of list elements. Lists offer more versatility than arrays, which can only hold items of the same kind.

Also, because lists are mutable, we can modify them at any time in the code after creating them. Throughout the program, we may change list items, insert new items, and delete any item.

Index Function

We can use the Python list index() function to locate a specific item in a Python list. A built-in function called list index() looks for an entry in a given list and returns the index of that item.

The function gives the index of the very first instance of an element if it occurs multiple times. In Python, the indexing begins from 0, not 1. Therefore, we may determine an item's position in the given list using an index.

The index() function's syntax is as follows:

Syntax

Let's break it down:

We first give the list's name, i.e., listt, in the syntax above.

• index() is the search technique that uses three parameters. Two parameters are optional, while one is mandatory.
• The necessary argument is item. The item whose index we are looking for is this one.
• The first optional argument is start. You will begin your search in the list from this index.
• The second optional argument is the end. You will finish your search in the list at this index.

Code

Output:

2
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
 in 
      9 
     10 # Getting index of an element that is not in the list
---> 11 index1 = info.index(34)
     12 print(index1)
     13 

ValueError: 34 is not in list

Find Multiple Indices in the List

We can use the built-in Python enumerate() method to keep track of and save the index when the item matches with the item we have given in the condition to find multiple indices of an item:

Code

Output:

[1, 2]
[1, 2]

Python Searches an Item in the List Using a For Loop

The simplest method is to conduct a linear search, for instance.

1. Beginning with the item on the left of the list, compare i with each item one at a time.
2. Return True if i matches an object.
3. Return False if none of the items in i match.

See the code below.

Code

Output:

Item is found in the list
Item not found in the list

Using the Python "in" operator

We will use the Python in operator to determine whether an element is present in the list.

Syntax

If an item is present in the list, the operation will return True; otherwise, it will give False.

Let us look at the following code.

Code

Output:

Item is found in the list
Item not found in the list

Filtering a Collection in Python

Using the list comprehension or generator functions to locate every element in a sequence that satisfies certain criteria.

Code

Output:

A string of length 5 is found in the list
A string of length 6 is not found in the list