Convert Values to Lists in Python

Introduction

In Python, sometimes we need to convert a value into a list. However, if the value is already a list, we don't want to create a nested list. In this challenge, you will create a function that takes a value and returns it as a list, unless it is already a list or another iterable.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL python(("Python")) -.-> python/ControlFlowGroup(["Control Flow"]) python(("Python")) -.-> python/DataStructuresGroup(["Data Structures"]) python(("Python")) -.-> python/FunctionsGroup(["Functions"]) python(("Python")) -.-> python/PythonStandardLibraryGroup(["Python Standard Library"]) python(("Python")) -.-> python/BasicConceptsGroup(["Basic Concepts"]) python/BasicConceptsGroup -.-> python/variables_data_types("Variables and Data Types") python/BasicConceptsGroup -.-> python/comments("Comments") python/ControlFlowGroup -.-> python/conditional_statements("Conditional Statements") python/DataStructuresGroup -.-> python/lists("Lists") python/DataStructuresGroup -.-> python/tuples("Tuples") python/FunctionsGroup -.-> python/function_definition("Function Definition") python/FunctionsGroup -.-> python/build_in_functions("Build-in Functions") python/PythonStandardLibraryGroup -.-> python/data_collections("Data Collections") subgraph Lab Skills python/variables_data_types -.-> lab-13597{{"Cast to List"}} python/comments -.-> lab-13597{{"Cast to List"}} python/conditional_statements -.-> lab-13597{{"Cast to List"}} python/lists -.-> lab-13597{{"Cast to List"}} python/tuples -.-> lab-13597{{"Cast to List"}} python/function_definition -.-> lab-13597{{"Cast to List"}} python/build_in_functions -.-> lab-13597{{"Cast to List"}} python/data_collections -.-> lab-13597{{"Cast to List"}} end

Cast to List

Write a function cast_list(val) that takes a value as an argument and returns it as a list. If the value is already a list, return it as is. If the value is not a list but is iterable, return it as a list. If the value is not iterable, return it as a single-item list.

def cast_list(val):
  return list(val) if isinstance(val, (tuple, list, set, dict)) else [val]

cast_list('foo') ## ['foo']
cast_list([1]) ## [1]
cast_list(('foo', 'bar')) ## ['foo', 'bar']

Summary

In this challenge, you learned how to create a function that casts a value to a list if it is not already a list or another iterable. You used isinstance() to check if the value is iterable and returned it using list() or encapsulated it in a list accordingly.