CODEWITHSUNDEEP
python
Adebayo Yusuf
Adebayo Yusuf

Reputation: 21

ValueError: not enough values to unpack (expected 3, got 1) when using split()

I keep getting this error:

x, y, z = expression.split(" ") 
ValueError: not enough values to unpack (expected 3, got 1)

This is my code:

expression = input("Expression: ")
# Parse variables.
x, y, z = expression.split(" ")
new_x=float(x)
new_z=float(z)
#calculate
if y == "+":
    result = new_x + new_z
if y == "-":
    result = new_x - new_z
if y == "*":
    result = new_x * new_z
if y == "/":
    result= new_x / new_z
print(round(result, 1))

Upvotes: 1

Views: 3252

Answers (2)

Nathaniel Ford
Nathaniel Ford

Reputation: 21230

The issue is that the input does not have enough delimited fragments to split into three pieces. You can play with this in the REPL:

>>> x, y, z = "a b c".split(" ")
>>> x
'a'
>>> y
'b'
>>> z
'c'
>>> x, y, z = "a b".split(" ")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: not enough values to unpack (expected 3, got 2)
>>> x, y, z = "a".split(" ")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: not enough values to unpack (expected 3, got 1)

For your use case where you are accepting input, the best bet is to handle this specific exception.

valid_input = false
x, y, z = None, None, None
while not valid_input:
  try:
    expression = input("Expression: ")
    x, y, z = expression.split(" ")
    valid_input = true
  except ValueError:
    print("Invalid input provided. Be sure to provide input with exactly 2 spaces in it!")

...  # Continue with the rest of your code

Another way to do this is:

def input_expression(attempt: int = 0) -> [str, str, str]:
  if attempt > 3:
    raise Exception("Too many invalid attempts. Quitting.")
  try:
    expression = input("Expression: ")
    x, y, z = expression.split(" ")
    return x, y, z
  except ValueError:
    print("Invalid input provided. Be sure to provide input with exactly 2 spaces in it!")
    return input_expression(attempt + 1)

x, y, z = input_expression()
... # The rest of your code

Upvotes: 1

Ahmad
Ahmad

Reputation: 349

it means that expression.split(" ") returns only one value, but since you unpacked its value to three variables x,y,z, it should return three values. So the problem is actually with your input.

Upvotes: 1

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