Lists and Strings

 Splitting

str_var.split(separator)

Splits a string into a list at every specified separator. If no separator is specified, default separator is whitespace.

Code

1

2

3

nums = "1 2 3 4"

num_list = nums.split()

print(num_list)

PYTHON

Output

['1', '2', '3', '4']

Multiple WhiteSpaces

Multiple whitespaces are considered as single when splitting.

Code

1

2

3

nums = "1 2 3 4 "

num_list = nums.split()

print(num_list)

PYTHON

Output

['1', '2', '3', '4']

New line

\n

and tab space

\t

are also whitespace.

Code

1

2

3

nums = "1\n2\t3 4"

num_list = nums.split()

print(num_list)

PYTHON

Output

['1', '2', '3', '4']

Using Separator

Breaks up a string at the specified separator.

Example -1

Code

1

2

3

nums = "1,2,3,4"

num_list = nums.split(',')

print(num_list)

PYTHON

Output

['1', '2', '3', '4']

Example -2

Code

1

2

3

nums = "1,2,,3,4,"

num_list = nums.split(',')

print(num_list)

PYTHON

Output

['1', '2', '', '3', '4', '']

Space as Separator

Code

1

2

3

nums = "1 2 3 4 "

num_list = nums.split(" ")

print(num_list)

PYTHON

Output

['1', '', '2', '3', '4', '']

String as Separator

Example - 1

Code

1

2

3

string_a = "Python is a programming language"

list_a = string_a.split('a')

print(list_a)

PYTHON

Output

['Python is ', ' progr', 'mming l', 'ngu', 'ge']

Example - 2

1

2

3

string_a = "step-by-step execution of code"

list_a = string_a.split('step')

print(list_a)

PYTHON

Output

['', '-by-', ' execution of code']

Joining

str.join(sequence)

Takes all the items in a sequence of strings and joins them into one string.

Code

1

2

3

list_a = ['Python is ', ' progr', 'mming l', 'ngu', 'ge']

string_a = "a".join(list_a)

print(string_a)

PYTHON

Output

Python is a programming language

Joining Non String Values

Sequence should not contain any non-string values.

Code

1

2

3

list_a = list(range(4))

string_a = ",".join(list_a)

print(string_a)

PYTHON

Output

TypeError: sequence item 0: expected str instance, int found

Negative Indexing

Using a negative index returns the nth item from the end of list.

Last item in the list can be accessed with index

-1

Reversing a List

-1

for step will reverse the order of items in the list.

Code

1

2

3

list_a = [5, 4, 3, 2, 1]

list_b = list_a[::-1]

print(list_b)

PYTHON

Output

[1, 2, 3, 4, 5]

Accessing List Items

Example-1

Code

1

2

3

list_a = [5, 4, 3, 2, 1]

item = list_a[-1]

print(item)

PYTHON

Output

1

Example-2

Code

1

2

3

list_a = [5, 4, 3, 2, 1]

item = list_a[-4]

print(item)

PYTHON

Output

4

Slicing With Negative Index

You can also specify negative indices while slicing a List.

Code

1

2

3

list_a = [5, 4, 3, 2, 1]

list_b = list_a[-3:-1]

print(list_b)

PYTHON

Output

[3, 2]

Out of Bounds Index

While slicing, Index can go out of bounds.

Code

1

2

3

list_a = [5, 4, 3, 2, 1]

list_b = list_a[-6:-2]

print(list_b)

PYTHON

Output

[5, 4, 3]

Negative Step Size

variable[start:end:negative_step]

Negative Step determines the decrement between each index for slicing.

Start index should be greater than the end index in this case

• start > end

Negative Step Size Examples

Example - 1

Code

1

2

3

list_a = [5, 4, 3, 2, 1]

list_b = list_a[4:2:-1]

print(list_b)

PYTHON

Output

[1, 2]

Example - 2

Negative step requires the start to be greater than end.

Code

1

2

3

list_a = [5, 4, 3, 2, 1]

list_b = list_a[2:4:-1]

print(list_b)

PYTHON

Output

[]

Reversing a List

-1

for step will reverse the order of items in the list.

1

2

3

list_a = [5, 4, 3, 2, 1]

list_b = list_a[::-1]

print(list_b)

PYTHON

Output

[1, 2, 3, 4, 5]

Reversing a String

-1

for step will reverse the order of the characters.

Code

1

2

3

string_1 = "Program"

string_2 = string_1[::-1]

print(string_2)

PYTHON

Output

margorP

Negative Step Size - Strings

Code

1

2

3

string_1 = "Program"

string_2 = string_1[6:0:-2]

print(string_2)

PYTHON

Output

mro

Indexing & Slicing - Strings

Example - 1

Code

1

2

3

string_1 = "Program"

string_2 = string_1[-1]

print(string_2)

PYTHON

Output

m

Example - 2

Code

1

2

3

string_1 = "Program"

string_2 = string_1[-4:-1]

print(string_2)

PYTHON

Output

gra