index Examples

The general syntax for this methods is:

list_name.index(value)

index returns the index of the FIRST occurrence of value in the list. If the value is not in the list, Python throws an error.

Examples

letters = ['o', 'y', 'j', 'j', 'g', 'f', 'h', 'y', 'j', 'x']

print(letters.index('j'))
print(letters.index('nope!'))

Console Output

2
ValueError: 'nope!' is not in list

Finding All Index Values

Often, we want to return all of the index values for a given search. One way to accomplish this is by using a loop:

Example

letters = ['o', 'y', 'j', 'j', 'g', 'f', 'h', 'y', 'j', 'x']
index_values = []
search_value = 'j'

for index in range(len(letters)):
   if letters[index] == search_value:
      index_values.append(index)

print("{0} has indexes of {1} in the list.".format(search_value, index_values))

Console Output

j has indexes of [2, 3, 8] in the list.

Note

Returning all index values for a given search is such a common task that Python coders have found a short, elegant way to do it:

index_values = [index for index in range(len(list_name)) if list_name[index] == search_value]

This does the same thing as the for loop shown in the example above. (Take a close look at the code to find the for and if statements).

We will not analyze the syntax here, but if you are curious, you can find an explanation here.