Python Slicing Working with examples

The concept of slicing in Python makes it very efficient to work with strings, lists, or tuples to extract a section from them with the help of range and indices.

Syntax:

sequence[start:end:step]

Let's try to understand each of the parameters here,

Parameter	Description	Default Value
start	Starting index of the slice (inclusive)	0
end	Ending index of the slice (exclusive)	Length of sequence
step	Step size between elements in the slice	1

Slicing with Strings Example:

Now let's start with a simple example of a string as a sequence.

sequence = "Let's try to learn sequences in Python!"

Slice	Result
'Let's'	Start: 0, End: 6, Step: 1
'sequences in Python!'	Start: 19, End: None, Step: 1
'to learn'	Start: 8, End: 16, Step: 1
'Let's try to learn sequences'	Start: 0, End: 23, Step: 1
'Python!'	Start: 25, End: None, Step: 1
'Let's in!'	Start: 0, End: 14, Step: 2
'!'	Start: -1, End: None, Step: 1
'Pytse ie'	Start: 26, End: 5, Step: -1

Once you get an understanding of how to slice what substring you are looking for, we can convert it into code.

Code:

sequence = "Let's try to learn sequences in Python!"

print(sequence[0:6])          # Result: "Let's"
print(sequence[19:])          # Result: "sequences in Python!"
print(sequence[8:16])         # Result: "to learn"
print(sequence[0:28])         # Result: "Let's try to learn sequences"
print(sequence[32:])          # Result: "Python!"
print(sequence[0:14:8])       # Result: "Ly"
print(sequence[-1:])          # Result: "!"
print(sequence[26:5:-1])      # Result: "ecneuqes nrael ot yrt"

Slicing with Lists Example:

Slice	Result
"Let's"	Start: 0, End: 6, Step: 1
"sequences in Python!"	Start: 19, End: None, Step: 1
"to learn"	Start: 8, End: 16, Step: 1
"Let's try to learn sequences"	Start: 0, End: 28, Step: 1
"Python!"	Start: 32, End: None, Step: 1
"Ly"	Start: 0, End: 14, Step: 8
"!"	Start: -1, End: None, Step: 1
"ecneuqes nrael ot yrt"	Start: 26, End: 5, Step: -1

Code:

list = [0.596, 0.105, 0.782, 0.421, 0.914, 0.290, 0.682, 0.813]

import random

decimal_numbers = [random.random() for _ in range(8)]
print(decimal_numbers)                    # Result: [0.596, 0.105, 0.782, 0.421, 0.914, 0.290, 0.682, 0.813]
print(decimal_numbers[0:])                # Result: [0.596, 0.105, 0.782, 0.421, 0.914, 0.290, 0.682, 0.813]
print(decimal_numbers[3:7])                # Result: [0.421, 0.914, 0.290, 0.682]
print(decimal_numbers[0:7:3])              # Result: [0.596, 0.782, 0.290]
print(decimal_numbers[-1::-1])             # Result: [0.813, 0.682, 0.290, 0.914, 0.421, 0.782, 0.105, 0.596]
print(decimal_numbers[-5:-1])              # Result: [0.105, 0.290, 0.682, 0.782]
print(decimal_numbers[3::2])               # Result: [0.421, 0.290, 0.105]
print(decimal_numbers[2:0:-1])             # Result: [0.682, 0.290, 0.421, 0.782]
print(decimal_numbers[4::-1])              # Result: [0.914, 0.421, 0.782, 0.105, 0.596]

Slicing with tuple Example:

cities = ('New York', 'Paris', 'London', 'Tokyo')

Slice	Result
('New York',)	Start: 0, End: 1, Step: 1
('Paris', 'London')	Start: 1, End: None, Step: 1
('Tokyo',)	Start: 2, End: 3, Step: 1
('New York', 'Paris', 'London', 'Tokyo')	Start: 0, End: None, Step: 1
('Tokyo', 'Paris')	Start: 2, End: None, Step: -1
()	Start: None, End: None, Step: None
('London', 'Paris', 'New York')	Start: -1, End: None, Step: -1
('Paris', 'London')	Start: 1, End: 3, Step: 1

Code:

cities = ('New York', 'Paris', 'London', 'Tokyo')

print(cities[0:1])                      # Result: ('New York',)
print(cities[1:])                       # Result: ('Paris', 'London', 'Tokyo')
print(cities[2:3])                      # Result: ('London',)
print(cities[0:])                       # Result: ('New York', 'Paris', 'London', 'Tokyo')
print(cities[3:1:-1])                   # Result: ('Tokyo', 'Paris')
print(cities[:])                        # Result: ('New York', 'Paris', 'London', 'Tokyo')
print(cities[-1:])                      # Result: ('Tokyo',)
print(cities[-2:-4:-1])                 # Result: ('London', 'Paris')

Some more examples:

Slice	Result	Description
sequence[:]	Entire sequence	Returns a new sequence that is a copy of the entire sequence.
sequence[::]	Entire sequence (equivalent to sequence[:])	Returns a new sequence that is a copy of the entire sequence.
sequence[::2]	Every second item	Returns a new sequence containing every second item.
sequence[1::2]	Every second item starting at index 1	Returns a new sequence containing every second item starting at index 1.
sequence[::-1]	Reversed sequence	Returns a new sequence with items in reverse order.
sequence[:5]	First five items	Returns a new sequence containing the first five items.
sequence[-5:]	Last five items	Returns a new sequence containing the last five items.
sequence[2:7]	Items from index 2 to 6	Returns a new sequence containing items from index 2 to 6.
sequence[1:-1]	Everything except the first and last items	Returns a new sequence excluding the first and last items.
sequence[::3]	Every third item	Returns a new sequence containing every third item.
sequence[:-2]	Everything except the last two items	Returns a new sequence excluding the last two items.
sequence[-3:-1]	Second-last and third-last items	Returns a new sequence containing the second-last and third-last items.
sequence[1:9:2]	Every second item from index 1 to 8	Returns a new sequence containing every second item from index 1 to 8.