Use items.index(target) to get the zero-based index of a value’s first occurrence in a Python list. To get every matching index, use enumerate() in a list comprehension. If the value is missing, list.index() raises ValueError.
Get the first matching index with list.index()
Call index() on the list and pass the value to find:
items = ["red", "blue", "red"]
target = "red"
first_index = items.index(target)
print(first_index) # 0The result is zero-based, so the first item is at index 0. Python’s official tutorial describes list.index(value) as returning the zero-based index of the first occurrence of the value.
Handle a value that might be absent
If no equal value is in the list, items.index(target) raises ValueError. When a missing value is an expected outcome, catch that exception:
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try:
position = items.index(target)
except ValueError:
position = NoneAlternatively, check membership before calling index():
if target in items:
position = items.index(target)
else:
position = NoneThe membership check is straightforward, but a successful lookup searches the list twice: once for in and again for index(). Catching ValueError avoids that repeated search.
Find every matching index
list.index() returns only the first position. To collect all positions, use enumerate() to pair each value with its index, then keep the indexes for values equal to the target:
items = ["red", "blue", "red"]
target = "red"
all_indexes = [i for i, value in enumerate(items) if value == target]
print(all_indexes) # [0, 2]If there are no matches, the comprehension returns an empty list, []. The Python tutorial documents enumerate() for retrieving a sequence’s position and corresponding value.
Limit the search with start and stop
You can pass optional bounds to index():
items.index(target, start, stop)The search covers the slice-like range beginning at start and ending before stop. The returned index is still measured from the beginning of the original list, not from start. To search for a later occurrence, start after the previous match. For finding an unknown number of matches, the enumerate() comprehension is generally clearer than repeatedly calling index().
Choose the method for the result you need
| Approach | What it returns | When no value matches |
|---|---|---|
items.index(target) |
The first matching index | Raises ValueError |
[i for i, value in enumerate(items) if value == target] |
A list of all matching indexes | Returns [] |
items.count(target) |
The number of matching values, not their positions | Returns 0 |
Use count() when you only need to know how many occurrences there are; use enumerate() when you need their locations. Python documents index(), count(), and the other list methods in its list reference.
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