Cara menggunakan list comprehension cubes python

Suppose, we want to separate the letters of the word

['h', 'u', 'm', 'a', 'n']

Example 1: Iterating through a string Using for Loop

h_letters = []

for letter in 'human':
    h_letters.append(letter)

print(h_letters)

When we run the program, the output will be:

['h', 'u', 'm', 'a', 'n']

However, Python has an easier way to solve this issue using List Comprehension. List comprehension is an elegant way to define and create lists based on existing lists.

Let’s see how the above program can be written using list comprehensions.

Example 2: Iterating through a string Using List Comprehension

h_letters = [ letter for letter in 'human' ]
print( h_letters)

When we run the program, the output will be:

['h', 'u', 'm', 'a', 'n']

In the above example, a new list is assigned to variable h_letters, and list contains the items of the iterable string 'human'. We call

['h', 'u', 'm', 'a', 'n']

Syntax of List Comprehension

[expression for item in list]

We can now identify where list comprehensions are used.

If you noticed,

['h', 'u', 'm', 'a', 'n']

You can do that using loops. However, not every loop can be rewritten as list comprehension. But as you learn and get comfortable with list comprehensions, you will find yourself replacing more and more loops with this elegant syntax.

List Comprehensions vs Lambda functions

List comprehensions aren’t the only way to work on lists. Various built-in functions and lambda functions can create and modify lists in less lines of code.

Example 3: Using Lambda functions inside List

letters = list(map(lambda x: x, 'human'))
print(letters)

When we run the program, the output will be

['h','u','m','a','n']

However, list comprehensions are usually more human readable than lambda functions. It is easier to understand what the programmer was trying to accomplish when list comprehensions are used.

Conditionals in List Comprehension

List comprehensions can utilize conditional statement to modify existing list (or other tuples). We will create list that uses mathematical operators, integers, and range().

Example 4: Using if with List Comprehension

number_list = [ x for x in range(20) if x % 2 == 0]
print(number_list)

When we run the above program, the output will be:

[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

The list ,number_list, will be populated by the items in range from 0-19 if the item's value is divisible by 2.

Example 5: Nested IF with List Comprehension

num_list = [y for y in range(100) if y % 2 == 0 if y % 5 == 0]
print(num_list)

When we run the above program, the output will be:

['h', 'u', 'm', 'a', 'n']

Here, list comprehension checks:

1. Is y divisible by 2 or not?
2. Is y divisible by 5 or not?

If y satisfies both conditions, y is appended to num_list.

Example 6: if...else With List Comprehension

['h', 'u', 'm', 'a', 'n']

When we run the above program, the output will be:

['h', 'u', 'm', 'a', 'n']

Here, list comprehension will check the 10 numbers from 0 to 9. If i is divisible by 2, then

h_letters = [ letter for letter in 'human' ]
print( h_letters)

h_letters = [ letter for letter in 'human' ]
print( h_letters)

Nested Loops in List Comprehension

Suppose, we need to compute the transpose of a matrix that requires nested for loop. Let’s see how it is done using normal for loop first.

Example 7: Transpose of Matrix using Nested Loops

['h', 'u', 'm', 'a', 'n']

Output

['h', 'u', 'm', 'a', 'n']

The above code use two for loops to find transpose of the matrix.

We can also perform nested iteration inside a list comprehension. In this section, we will find transpose of a matrix using nested loop inside list comprehension.

Example 8: Transpose of a Matrix using List Comprehension

['h', 'u', 'm', 'a', 'n']

When we run the above program, the output will be:

['h', 'u', 'm', 'a', 'n']

In above program, we have a variable matrix which have

h_letters = [ letter for letter in 'human' ]
print( h_letters)

h_letters = [ letter for letter in 'human' ]
print( h_letters)

**Note: The nested loops in list comprehension don’t work like normal nested loops. In the above program,

h_letters = [ letter for letter in 'human' ]
print( h_letters)

h_letters = [ letter for letter in 'human' ]
print( h_letters)

h_letters = [ letter for letter in 'human' ]
print( h_letters)