Possible reason 1: trying to create a jagged array
You may be creating an array from a list that isn’t shaped like a multi-dimensional array:
numpy.array([[1, 2], [2, 3, 4]]) # wrong!
numpy.array([[1, 2], [2, [3, 4]]]) # wrong!
In these examples, the argument to numpy.array contains sequences of different lengths. Those will yield this error message because the input list is not shaped like a “box” that can be turned into a multidimensional array.
Possible reason 2: providing elements of incompatible types
For example, providing a string as an element in an array of type float:
numpy.array([1.2, "abc"], dtype=float) # wrong!
If you really want to have a NumPy array containing both strings and floats, you could use the dtype object, which allows the array to hold arbitrary Python objects:
numpy.array([1.2, "abc"], dtype=object)