Python valueerror: too many values to unpack (expected 2) Solution

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Python valueerror: too many values to unpack (expected 2) Solution
vinaykhatri

Vinay Khatri
Last updated on April 14, 2024

    Python valueerror: too many values to unpack (expected 2) is an unpacking error that occurs when we try to unpack fewer variables than the actual number of elements present in the iterator.

    In this Python guide, we will walk through this error and discuss why it is raised and how to solve it. We will also see some examples which will give you a broad idea of why this error occurs and how to debug it. So let's get started with the Problem itself.

    The Problem: valueerror: too many values to unpack (expected 2)

    The error statement is divided into parts

    1. valueerror
    2. too many values to unpack(expected 2)

    The valueerror in Python specifies that we are doing something wrong with assigning values to an object. And the statement too many values to unpack(expected 2) specifies the main error. It defines that the unpacking variables are less than the total number of iterators present in the iterator.

    Python unpacking is a technique to assign values of an iterable object to multiple elements using a single statement.

    Python unpacking Example

    # list
    greeting = ["Hi", "Hello", "Hey"]
    
    # python unpacking
    opt1, opt2, opt3 = greeting
    
    print("opt1:", opt1)
    print("opt2:", opt2)
    print("opt3:", opt3)

    Output

    opt1: Hi
    opt2: Hello
    opt3: Hey

    In our above example, we unpacked our greeting iterable(list) into 3 variables opt1 , opt2 and opt3 using the statement opt1, opt2, opt3 = greeting .

    If we analyze it, we can see that the number of variables to which we assigned the values is equal to the number of elements present in the list greeting . But if we reduce the number of variables only to 2, we would receive the error too many values to unpack(expected 2) .

    Example

    # list
    greeting = ["Hi", "Hello", "Hey"]
    
    # unpacking only two values
    opt1, opt2 = greeting
    
    print("opt1:", opt1)
    print("opt2:", opt2)

    Output

    Traceback (most recent call last):
    File "main.py", line 5, in <module>
    opt1, opt2 = greeting
    ValueError: too many values to unpack (expected 2)

    Break the Output

    We are receiving this error because the greeting list has 3 elements, but during unpacking, the statement at line 5 we are only unpacking 2 variables opt1 and opt2 , which is illegal. During iterable unpacking Python interpreter expect the n number of variables at the left side of the assignment operator, where n is the total number of elements present in the list.

    If the variables on the left side during iterable unpacking are greater than 1 and less than n, we receive the error ValueError: too many values to unpack (expected n) . The error message itself describes that the list has many elements to unpack, but we are specifying fewer variable names.

    Solutions

    There are two solutions to this problem.

    Solution 1 (unpack all values)

    The first solution is very straightforward. We just need to specify the equal number of variables on the left side of the assignment as the number of elements we have in the iterable.

    Example

    # list
    greeting = ["Hi", "Hello", "Hey"]
    
    # unpacking all the values
    opt1, opt2, opt3 = greeting
    
    print("opt1:", opt1)
    print("opt2:", opt2)
    print("opt3:", opt3)

    Output

    opt1: Hi
    opt2: Hello
    opt3: Hey

    Solution 2 (use *_ variable)

    It is also possible that an iterable has millions of elements, and you only wish to unpack the first two values. In that case, we can't use million variable names only to unpack the first two values. You could also say we can use Python slicing, but it will only be available for sets and dictionaries.

    So, in such cases, we can use the *_ variable name after the number of variables we want to unpack. The *_ variable represents a throw-away variable for the list. * the symbol represents multiple arguments, and the _ variable name represents a throwaway variable that we will not use in our program.

    Example

    # list
    greeting = ["Hi", "Hello", "Hey"]
    
    # unpacking only two values
    opt1, opt2, *_ = greeting
    
    print("opt1:", opt1)
    print("opt2:", opt2)

    Output

    opt1: Hi
    opt2: Hello

    Conclusion

    In this Python tutorial, we discussed the Python error valueerror: too many values to unpack (expected 2) and how to solve it. The 2 in the error message is the number of variables we are trying to unpack and it could be any number greater than 1 and less than n, where n is the total number of elements present in the iterable object.

    If you only want to unpack a limited number of elements from an iterable object there, you can use the *_ variable name, it will store all rest of the values of an iterable object in the throwaway list. If you are still getting the error in your Python program, please comment down your code, and we will try to debug it for you.

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