[Term Entry] Python deque: index() (Codecademy#7755)

content/python/concepts/deque/terms/index/index.md

@@ -0,0 +1,104 @@
+---
+Title: 'index'
+Description: 'Returns the position of the first occurrence of a specified element within the deque.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Algorithms'
+  - 'Collections'
+  - 'Data Structures'
+  - 'Deques'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/computer-science'  
+---
+
+The **`index()`** method in a Python [deque](https://www.codecademy.com/resources/docs/python/collections-module/deque) returns the position of the first occurrence of a specified element within the deque.
+
+## Syntax
+
+```pseudo
+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](https://www.codecademy.com/resources/docs/python/keywords/try) block.
+
+## Example 1: Finding elements by position
+
+In this example, `index()` is used to find the position of elements in different scenarios:
+
+```py
+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)
+```
+
+The output of this code is:
+
+```shell
+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 give you problems.
+10 is not in deque
+```
+
+## Example 2: 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:
+
+```py
+from collections import deque
+
+# Create a deque with some initial elements
+fruits = deque(["apple", "banana", "apple", "lemon", "apple", "tomato"])
+
+# Find the index for the first occurrence of "apple"
+first_occurrence_of_apple_index = fruits.index("apple")
+print("First found index for apple:", first_occurrence_of_apple_index)
+
+# Find the next occurrence of "apple" after the first occurrence
+print("Next occurrence:", fruits.index("apple", first_occurrence_of_apple_index + 1))
+
+# Find the index for "apple" between index=1 inclusive and index=4 exclusive
+print("Index for apple between (1) inclusive and (4) exclusive:", fruits.index("apple", 1, 4))
+```
+
+The output of this code is:
+
+```shell
+First found index for apple:  0
+Next occurrence:  2
+Index for apple, between (1) inclusive and (4) exclusive:  2
+```