Python index

The index() method in a Python deque returns the position of the first occurrence of a specified element within the deque.

Syntax

deque.index(element, start=0, stop=len(deque))

Parameters:

• element: The element to be found within the deque.
• start (Optional): The zero-based inclusive index to specify the start position of the search.
• stop (Optional): The index to end the search (default is the length of the deque).

Return value:

Returns the index (int) of the first matching element; raises a ValueError if the element is not found.

Note: This method raises a ValueError if the element is not in the deque, which can stop the code if not handled inside a try and except block.

Example 1: Finding elements by position

In this example, index() is used to find the position of elements in different scenarios:

from collections import deque

# Create a deque
dq = deque([1, 2, 3, 1, 4, 5, 1])

# Find the very first position of (4)
print("Very first position of (4):", dq.index(4))

# Find the position of (1) after index=0
start = 0 + 1  # Since the start parameter is inclusive, add 1 to skip index=0.
print("Position of (1) after index=0:", dq.index(1, 1))

# Find the position of (1) in a given window
start = 1
stop = 6
print("Position of (1) between index=1 inclusive and index=6 exclusive:", dq.index(1, 1, 6))

# Find the position of (10), which is not in the deque
try:
  print("Position of (10):", dq.index(10))
except ValueError as ve:
  print("Trying to find the index of a nonexistent element will cause an error.")
  print(ve)

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The output of this code is:

Very first position of (4): 4
Position of (1) after index=0: 3
Position of (1) between index=1 inclusive and index=6 exclusive: 3
Trying to find the index of a nonexistent element will cause an error.
10 is not in deque

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Codebyte Example: Finding elements by value range

In this example, index() finds the position of the element "apple" in different scenarios, showing its flexibility and use of parameters:

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