Reference · General

len

len(str | list | map | html | null) -> int

What it does

The size of a value: a string's characters, a list's items, a map's keys, and an html value's bytes. null has length 0, so a missing list or text counts as empty. x.len is the same as len(x).

Examples

print(len("hello"), len([1, 2, 3]), len({ a: 1, b: 2 }))print(len(""), len([]), len({}))

5 3 20 0 0

Edge cases

• Characters, not bytes: len("é") and len("😀") are 1.
• null is 0, not an error.
• A list counts its items only, not what is inside them: [[1, 2], [3]] has length 2.
• An html value's length is its bytes, as sent to the browser.
• Splitting the empty string gives one empty piece, so its length is 1, not 0.

print(len("é"), len("😀"), len("héllo"), len("a\nb"))print(len(null), len([[1, 2], [3]]))print(len(<b>hi</b>))print(len(split("", ",")))

1 1 5 30 291

Errors

A number, a boolean or a function has no length: that is a runtime error, not an error value. Convert a number with str first.

print(len(42))

line 1: `len` expects a str, list or map, got int

Chaining

print(123 | str | len)print("a,b,c" | split(",") | len)print(["ab", "", "c"] | filter((s) => len(s) > 0) | len)

332

See also

slice, split, count, str, contains

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