Converting to and from Python lists in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you convert a Python list to a NumPy array?

Use numpy.array() function. For example, np.array([1, 2, 3]) converts the list [1, 2, 3] to a NumPy array.

beginner

How do you convert a NumPy array back to a Python list?

Use the tolist() method of the NumPy array. For example, arr.tolist() converts the array arr to a Python list.

beginner

What is the difference between a Python list and a NumPy array?

A Python list can hold items of different types and is flexible but slower. A NumPy array holds items of the same type and is optimized for fast numerical operations.

intermediate

Can you convert a nested Python list to a NumPy array? How?

Yes, you can convert nested lists (lists of lists) to multi-dimensional NumPy arrays using np.array(). For example, np.array([[1, 2], [3, 4]]) creates a 2x2 array.

intermediate

What happens if you convert a NumPy array with mixed data types to a list?

The tolist() method converts the array elements to native Python types, preserving the structure. If the array has mixed types, the list will contain those types as Python objects.

Which function converts a Python list to a NumPy array?

A array.tolist()

B numpy.tolist()

C numpy.array()

D list()

The numpy.array() function converts a Python list to a NumPy array.

How do you convert a NumPy array named arr to a Python list?

A arr.tolist()

B arr.to_list()

C list(arr)

D numpy.list(arr)

Use the tolist() method: arr.tolist().

What type of data structure does np.array() create from a list?

A NumPy array

B Python list

C Dictionary

D Tuple

np.array() creates a NumPy array.

Can np.array() convert a nested list into a multi-dimensional array?

A Only for 1D lists

B No

C Only if the nested lists are the same length

D Yes

Yes, np.array() can convert nested lists into multi-dimensional arrays.

What does arr.tolist() return?

A A NumPy array

B A Python list

C A Python tuple

D A Python dictionary

arr.tolist() returns a Python list.

Explain how to convert a Python list to a NumPy array and back to a list.

Think about the functions and methods used for conversion.

Describe the difference between Python lists and NumPy arrays in terms of data type and performance.

Consider flexibility vs speed.