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Python list()

The list() constructor returns a list in Python.

The syntax of list() is:

list([iterable])

list() Parameters

The list() constructor takes a single argument:

  • iterable (optional) - an object that could be a sequence (string, tuples) or collection (set, dictionary) or any iterator object

Return value from list()

The list() constructor returns a list.

  • If no parameters are passed, it returns an empty list
  • If iterable is passed as a parameter, it creates a list consisting of iterable's items.

Example 1: Create lists from string, tuple, and list

# empty list
print(list())

# vowel string
vowel_string = 'aeiou'
print(list(vowel_string))

# vowel tuple
vowel_tuple = ('a', 'e', 'i', 'o', 'u')
print(list(vowel_tuple))

# vowel list
vowel_list = ['a', 'e', 'i', 'o', 'u']
print(list(vowel_list))

Output

[]
['a', 'e', 'i', 'o', 'u']
['a', 'e', 'i', 'o', 'u']
['a', 'e', 'i', 'o', 'u']

Example 2: Create lists from set and dictionary

# vowel set
vowel_set = {'a', 'e', 'i', 'o', 'u'}
print(list(vowel_set))

# vowel dictionary
vowel_dictionary = {'a': 1, 'e': 2, 'i': 3, 'o':4, 'u':5}
print(list(vowel_dictionary))

Output

['a', 'o', 'u', 'e', 'i']
['o', 'e', 'a', 'u', 'i']

Note: In the case of dictionaries, the keys of the dictionary will be the items of the list. Also, the order of the elements will be random.


Example 3: Create a list from an iterator object

# objects of this class are iterators
class PowTwo:
    def __init__(self, max):
        self.max = max
    
    def __iter__(self):
        self.num = 0
        return self
        
    def __next__(self):
        if(self.num >= self.max):
            raise StopIteration
        result = 2 ** self.num
        self.num += 1
        return result

pow_two = PowTwo(5)
pow_two_iter = iter(pow_two)

print(list(pow_two_iter))

Output

[1, 2, 4, 8, 16]

Recommended Reading: Python List