## List

List is a changeable and ordered data type that allows it to be indexed and sliced. It can contain heterogeneous values such as integers, floats, strings, tuples, lists, and dictionaries but they are commonly used to store collections of homogeneous objects.

### Python program to check if a list is empty or not

1 2 3 4 5 6 7 |
empty_list = [] if empty_list: print("List is not empty") else: print("List is empty") #Output: List is empty |

- Python treats everything as an object and objects are always true in python. However, null values, None, 0, empty data types are observed as false in python.

### Python program to create a list of empty dictionaries

1 2 3 4 |
num = 8 #no of empty dictionaries in list list = [ {} for i in range(num)] #list comprehension print(list) #Output: [{}, {}, {}, {}, {}, {}, {}, {}] |

List comprehension is a compact method that defines a list and its contents at the same time. The basic syntax of list comprehension consists of a square bracket with an expression that is executed for each element along with for loop to iterate over each element.

**Read more on list comprehension:***http://betapython.com/list-comprehension-in-python-explained-with-examples/*

### Python program to find the sum of all the elements in a list

1 2 3 4 5 6 7 8 9 10 11 12 13 |
list = [11, 20, 4, 23, -9] #using loops sum = 0 for i in list: #iterating through each item in list sum = sum + i print(sum) #Output: 49 #using built-in sum() method sum = sum(list) print(sum) #Output: 49 |

- The sum() built-in method sums up all the numbers present in the list.

### Python program to find the average of all the numbers in a list

The average of all the numbers in a list can be simply calculated by using the sum() and len() function.

- The len() function returns the number of s in elements present in an object.

1 2 3 4 |
list = [7, 1, 16, 10, 12, 13] average = int(sum(list) / len(list)) print(average) #Output: 9 |

### Python program to find the second largest number in a list

1 2 3 4 5 6 7 8 9 10 11 12 |
list = [28, 77, 35, 52, 11] #using sort() built-in list method list.sort(reverse = True) #Sorting all the elements of a list in descending order print(list[1]) #Output: 52 #using set(), remove() and max() built-in methods list_set = set(list) list_set.remove(max(list_set)) # removing the largest element from the set print(max(list_set)) #Output: 52 |

- The sort() built-in list method rearranges the list in-place in a particular order (ascending, descending, etc.).
- The set() built-in method creates a set. A set is an unordered collection of immutable and unique elements in python.
**To read more:**http://betapython.com/set-data-type-in-python/

- The max() built-in method returns the element with the highest value in an iterable.

### Python program to get a random element from a list

The random module is used to generate random numbers in python. This module implements pseudo-random number generators for various distributions.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 |
import random list = [29, 1, 71, 12, 88, 6, 32, 58, 93, 67, 75, 43, 97, 24] #using random.choice() random_num = random.choice(list) print(random_num) #Output: 12 #using random.random() random_num = int(random.random() * len(list)) print(random_num,list[random_num]) #Output: 6 32 #Using random.randrange() random_num = random.randrange(len(list)) print(random_num,list[random_num]) #Output: 8 93 #Using random.randint() random_num = random.randint(0,len(list)-1) print(random_num,list[random_num]) #Output: 4 88 |

- The
**random.choice()**returns a randomly selected element from a non-empty sequence. - The
**random.random()**generates a random float number between 0.0 and 1.0. This random float number is then multiplied with the length of the list and typecasted to int to get an integer index value for the list. - The
**random.randrange()**generates a random number in a range specified in its argument. This generated random number is then used as an index of the list. - The
**random.randint()**generates a random integer between the specified integers. This generated random integer is then used as an index of the list.