Python ValueError To many values to unpack

November 14, 2021

Iam struggling to understand why the first way works and the second throws error.
Suppose we have this array

interests =[(0,"Hadoop"),(0,"Big Data"),(0,"HBase"),(0,"Java"),(0,"Spark"),(0,"Storm"),(0,"Cassandra"),(1,"NoSQL",0),
            (1,"MongoDB"),(1,"Cassandra"),(1,"HBase"),(1,"Postgres"),(2,"Python"),(2,"scikit-learn"),(2,"scipy"),(2,"numpy"),
            (2,"statsmodels"),(2,"pandas"),(3,"R"),(3,"Python"),(3,"statistics"),(3,"regression"),(3,"probability"),
            (4,"machine learning"),(4,"regression"),(4,"decision trees"),(4,"libsvm"),(5,"Python"),(5,"R"),(5,"Java"),
            (5,"C++"),(5,"Haskell"),(5,"programming languages"),(6,"statistics"),(6,"probability"),(6,"mathematics"),
            (6,"theory"),(7,"machine learning"),(7,"scikit-learn"),(7,"Mahoot"),(7,"neural networks"),(8,"neural networks"),
            (8,"deep learning"),(8,"Big Data"),(8,"artificial intelligence"),(9,"Hadoop"),(9,"Java"),(9,"MapReduce"),
            (9,"Big Data")]

1)I want to iterate over the tuple-elements of this list like this.

for x, y in interests:
    print(x,y)

This works only for tuples with first element equals to 0 and then throws value error.
2)Below, this way works.

for interest in interests:
    print(interest[0],interest[1])

3)And lastly this way below also gives the same result with the first way.

for interest in interests:
    x,y = interest
    print(x,y)

I cant imagine how i can unpack correct the values

>Solution :

It’s only printing the first couple tuples(Until 0,"Cassandra") because the one right after it has 3 elements inside it – (1,"NoSQL",0), the for loop has only mentioned x,y (2)

You can use this instead –

interests =[(0,"Hadoop"),(0,"Big Data"),(0,"HBase"),(0,"Java"),(0,"Spark"),(0,"Storm"),(0,"Cassandra"),(1,"NoSQL",0),
            (1,"MongoDB"),(1,"Cassandra"),(1,"HBase"),(1,"Postgres"),(2,"Python"),(2,"scikit-learn"),(2,"scipy"),(2,"numpy"),
            (2,"statsmodels"),(2,"pandas"),(3,"R"),(3,"Python"),(3,"statistics"),(3,"regression"),(3,"probability"),
            (4,"machine learning"),(4,"regression"),(4,"decision trees"),(4,"libsvm"),(5,"Python"),(5,"R"),(5,"Java"),
            (5,"C++"),(5,"Haskell"),(5,"programming languages"),(6,"statistics"),(6,"probability"),(6,"mathematics"),
            (6,"theory"),(7,"machine learning"),(7,"scikit-learn"),(7,"Mahoot"),(7,"neural networks"),(8,"neural networks"),
            (8,"deep learning"),(8,"Big Data"),(8,"artificial intelligence"),(9,"Hadoop"),(9,"Java"),(9,"MapReduce"),
            (9,"Big Data")]
for x,y,*a in interests:
    print(x)
    print(y)