DevEquiv

    PHP in_array() Equivalent in Python

    Python's `in` operator replaces PHP's in_array() for membership tests, but PHP's default loose comparison can produce true where Python's `in` (which always compares by equality and type) would say false.

    Requires review

    PHP source
    in_array()
    Closest Python API
    in

    Main limitation: PHP `in_array($needle, $haystack)` defaults to loose (`==`) comparison, so `in_array("abc", [0, 1, 2])` is `true` in older PHP behavior due to string-to-number coercion quirks; Python's `in` never coerces types this way — `"abc" in [0, 1, 2]` is always `False`.

    How to use each function

    Before comparing the two, here's how in_array() and in work on their own.

    PHP: in_array()

    in_array(mixed $needle, array $haystack, bool $strict = false): bool

    Checks whether a value exists anywhere in an array. By default it uses loose (==) comparison, which can produce surprising type-coercion matches; passing true as the third argument forces strict (===) comparison.

    Returns: true if the value is found, false otherwise.

    PHP 
    $roles = ["admin", "editor", "viewer"];
in_array("editor", $roles); // true
in_array("0", [0, 1, 2], true); // false (strict)

    Python: in

    value in iterable

    A built-in operator, not a function, that tests membership by equality across lists, tuples, sets, strings, and dict keys. Unlike PHP's default loose in_array(), Python's in never coerces types — it only matches values of an equal type and value.

    Returns: True if a matching element exists, False otherwise.

    Python 
    "editor" in ["admin", "editor", "viewer"]  # True

    Quick mapping

    PHP in_array()
    Closest Python API in

    How it differs

    • PHP in_array($needle, $haystack) defaults to loose (==) comparison, so in_array("abc", [0, 1, 2]) is true in older PHP behavior due to string-to-number coercion quirks; Python's in never coerces types this way — "abc" in [0, 1, 2] is always False.
    • PHP's third $strict argument (in_array($needle, $haystack, true)) forces type-and-value comparison, which then matches Python's in semantics much more closely — prefer strict mode when translating to avoid surprises.
    • Python's in works on any iterable (lists, tuples, sets, strings, dict keys) with the same syntax; PHP's in_array() is specifically for arrays, with str_contains()/strpos() used for strings instead.

    Examples

    Basic membership check

    PHP 
    in_array("b", ["a", "b", "c"]); // true
    Python 
    "b" in ["a", "b", "c"]  # True
    A direct, exact translation for same-type values.

    Strict comparison to avoid type coercion

    PHP 
    in_array("1", [0, 1, 2], true); // false (strict)
    Python 
    "1" in [0, 1, 2]  # False
    PHP's strict mode is required here to match Python's always-strict `in` — without `true` as the third argument, PHP's loose comparison could behave differently depending on version and values involved.

    Edge cases

    Edge case

    Always use PHP's strict mode (in_array($needle, $haystack, true)) when porting to Python's in, since Python has no loose-comparison equivalent to translate exactly — otherwise the behavior can silently diverge for mixed-type arrays.

    Edge case

    For frequent membership checks against a large collection, Python's in on a set is O(1) average case, versus O(n) for a list — consider converting to a set if performance matters, mirroring how PHP developers sometimes flip an array to use isset() on keys instead.

    References

    • PHP Manual — in_array — checked 2026-07-29
    • Python docs — Comparisons — the `in` operator (v3.x) — checked 2026-07-29

    Last verified 2026-07-29.