ValueError: not enough values to unpack

What this error means

You assigned an iterable to more names than it has items. The message even does the arithmetic for you: expected 3, got 1 means three names on the left, one item on the right.

Unpacking is a length check, not a conversion. year, month, day = "2026-10-11" fails with too many values to unpack (11 characters, 3 names); year, month, day = parts fails with this error whenever parts came out shorter than three.

Cause 1 — split() with a separator that is not in the string

The single most common source. When the separator is absent, split() does not fail — it returns a one-item list containing the whole string, and the unpacking blows up:

row = "2026/10/11"
year, month, day = row.split("-")   # split returns ['2026/10/11']

Traceback (most recent call last):
  File "demo.py", line 2, in <module>
    year, month, day = row.split("-")
    ^^^^^^^^^^^^^^^^
ValueError: not enough values to unpack (expected 3, got 1)

Print the intermediate value and the cause is obvious: print(row.split("-")) → ['2026/10/11']. The real data used /, or the column is empty, or the file has Windows line endings and the last field is '11\r'. Always inspect the list before unpacking it.

Cause 2 — a row that is genuinely short

CSV rows, user input, API payloads and database rows do not all have the same width. One truncated line in a 10,000-line file is enough:

with open("scores.csv", encoding="utf-8") as f:
    for lineno, line in enumerate(f, start=1):
        parts = line.strip().split(",")
        if len(parts) != 3:
            print(f"line {lineno} has {len(parts)} fields: {parts!r}")
            continue
        name, subject, score = parts

Cause 3 — a function that returned fewer values

A function with two return paths — one returning a tuple, one returning None or a single value — unpacks fine on the happy path and fails on the other:

def split_name(full):
    if " " in full:
        first, last = full.split(" ", 1)
        return first, last
    return full            # one value, not two

first, last = split_name("Asha")   # ValueError: not enough values to unpack

Four ways to fix it

• Guard the length — check len(parts) and skip, log or raise a message that names the offending line. Best for files and user input.
• Take what you need with star unpacking — first, *rest = parts always succeeds when there is at least one item; first, *_, last = parts needs at least two. Use *_ to discard a variable tail.
• Supply defaults while unpacking — a, b, c = (parts + [None, None, None])[:3] pads short rows instead of crashing. Explicit and easy to read.
• Use partition when you only need one split — head, sep, tail = text.partition(":") never raises and tells you in sep whether the separator was found at all.

parts = row.split("-")
year, month, day = (parts + [None, None])[:3]   # tolerant, always three names

How to debug it

1. Print the right-hand side first: parts = row.split('-'); print(len(parts), parts). The count and the repr tell you everything.
2. Read the numbers in the message — expected 3, got 1 means three names on the left, one item on the right.
3. Check for a stray \r from Windows files: open with newline="" in the csv module, or .strip() each line.
4. If it comes from a function call, read every return in that function — they must all return the same shape.
5. For CSV, use csv.reader instead of str.split(','): it handles quoted fields that contain commas, which silently change the field count.

Fix it interactively

Unpacking practice, free in the browser:

• Multiple return values easy
• Tuple unpacking with functions medium

Related messages worth knowing

• too many values to unpack (expected 2) — the mirror error — the iterable is longer than the names.
• ValueError: the parent guide — right type of object, wrong value inside it.
• TypeError: string indices must be integers — the next error in line when you unpack a string by accident.