Python More Built-in Functions

Concepts

Built-in Functions

• abs()
• all()
• any()
• reversed()
• enumerate()

List Methods

• copy()
• reverse()

1. Built-in Functions

1.1 Abs

Syntax:

abs(number)

The

abs()

function gives the absolute value (positive representation) of a number. For example, the absolute value of

-3

is

3

.

Example 1:

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num = -4

abs_value = abs(num)

print(abs_value)

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Output

4

Example 2:

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print(abs(5))

print(abs(-2.90))

print(abs(3 - 5))

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Output

5

2.9

2

1.2 All

Syntax:

all(sequence)

The

all()

function returns

True

if all the items in the sequence are true (or if the sequence is empty). Otherwise, it returns

False

.

For each item in a sequence, the

all()

function evaluates to false, for which the

bool()

function returns

False

. For example,

0

,

None

,

False

, etc.

Example 1:

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list_a = [True, True]

is_all_true = all(list_a)

print(is_all_true)

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Output

True

Example 2:

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set_a = {}

is_all_true = all(set_a)

print(is_all_true)

 

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Output

True

Example 3:

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is_true_in_list = all([1, 5, 0, 4])

is_true_in_set = all({True, "Teja", 7})

is_true_in_tuple = all(("", "hello", "world"))

print(is_true_in_list)

print(is_true_in_set)

print(is_true_in_tuple)

 

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Output

False

True

False

In the case of dictionaries, the

all()

function returns

True

if all the keys in the dictionary are true. Otherwise, it returns

False

.

Example 4:

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dict_a = {

"name": "Teja",

"age": 15

}

is_all_true = all(dict_a)

print(is_all_true)

 

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Output

True

Example 5:

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dict_a = {

0: "Hello",

1: "World"

}

is_all_true = all(dict_a)

print(is_all_true)

 

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Output

False

1.3 Any

Syntax:

any(sequence)

The

any()

function returns

True

if any of the items in the sequence is true. Otherwise, it returns

False

.

If the sequence is empty, it returns

False

.

For each item in a sequence, the

any()

function evaluates to false, for which the

bool()

function returns

False

. For example,

0

,

None

,

False

, etc.

Example 1:

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list_a = [True, False]

is_any_true = any(list_a)

print(is_any_true)

 

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Output

True

Example 2:

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set_a = {}

is_any_true = any(set_a)

print(is_any_true)

 

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Output

False

Example 3:

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is_true_in_list = any([0, 0, 2, 0])

is_true_in_set = any({"", None, 0})

is_true_in_tuple = any(("hello", "world"))

print(is_true_in_list)

print(is_true_in_set)

print(is_true_in_tuple)

 

PYTHON

Output

True

False

True

In the case of dictionaries, the

any()

function returns

True

if any of the keys in the dictionary is true. Otherwise, it returns

False

.

Example 4:

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dict_a = {

0: "Teja",

1: 15

}

is_any_true = any(dict_a)

print(is_any_true)

 

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Output

True

Example 5:

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dict_a = {

0: "hello",

False: "world"

}

is_any_true = any(dict_a)

print(is_any_true)

 

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Output

False

1.4 Reversed

Syntax:

reversed(sequence)

Here, the

sequence

does not include sets and dictionaries as they are unordered collections of items.

The

reversed()

function returns the reverse of a sequence.

Example 1:

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name = "Teja"

reversed_name = reversed(name)

print(list(reversed_name))

 

PYTHON

Output

['a', 'j', 'e', 'T']

Example 2:

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tuple_a = (1, 2, 3, 4)

list_a = ["A", "B", "C", "D"]

reversed_tuple = list(reversed(tuple_a))

reversed_list = list(reversed(list_a))

print(reversed_tuple)

print(reversed_list)

 

PYTHON

Output

[4, 3, 2, 1]

['D', 'C', 'B', 'A']

1.5 Enumerate

Syntax:

enumerate(sequence, start)

Here,

• sequence
  : is any sequence like a string, list, set, etc.
• start
  (Optional): it indicates the start point of the counter. Its default value is 
  0
  .

The

enumerate()

function adds a counter to each item in a sequence and returns a sequence containing tuples.

Example 1:

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name = "Teja"

enumerate_name = enumerate(name)

print(list(enumerate_name))

 

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Output

[(0, 'T'), (1, 'e'), (2, 'j'), (3, 'a')]

Example 2:

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set_a = {1, 2, 3, 4}

enumerate_set = list(enumerate(set_a, 10))

print(enumerate_set)

 

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Output

[(10, 1), (11, 2), (12, 3), (13, 4)]

Looping Over an Enumerate

We can use the

for

loop to iterate over an enumerate.

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names = ["Jack", "John", "James"]

for each_name in enumerate(names):

print(each_name)

 

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Output

(0, 'Jack')

(1, 'John')

(2, 'James')

We can unpack each tuple returned by the enumerate.

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names = ["Jack", "John", "James"]

for count, each_name in enumerate(names):

tuple_a = (count, each_name)

print(tuple_a)

 

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Output

(0, 'Jack')

(1, 'John')

(2, 'James')

2. List Methods

2.1 Copy

Syntax:

list.copy()

The

copy()

method returns a copy of the specified list. After copying, any changes made to the original list do not affect the items in the copied list.

Example 1:

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list_a = [1, 2, 3, 4]

list_b = list_a.copy()

print(list_b)

 

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Output

[1, 2, 3, 4]

Example 2:

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list_a = ["a", "b", "c"]

list_b = list_a

list_a[0] = "z"

print(list_b)

list_1 = ["a", "b", "c"]

list_2 = list_1.copy()

list_1[0] = "z"

print(list_2)

 

PYTHON

Output

['z', 'b', 'c']

['a', 'b', 'c']

In the above code, both the variables

list_a

and

list_b

will be referring to the same object. So, when an item in

list_a

is updated it affected

list_b

also.

Whereas, when we copy

list_1

using the

copy()

method, the variables

list_1

and

list_2

will refer to different objects. So, when an item in

list_1

is updated it does not affect

list_2

.

However, updating mutable objects will affect the values in the copied list also, as the reference is changed.

Example 3:

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list_a = ["a", "b", "c"]

list_b = [1, 2, 3, list_a]

list_c = list_b.copy()

list_a[0] = "z"

print(list_c)

 

PYTHON

Output

[1, 2, 3, ['z', 'b', 'c']]

2.2 Reverse

Syntax:

list.reverse()

The

reverse()

method reverses the items of the list. It doesn't return any value but updates the existing list.

Example 1:

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list_a = [1, 2, 3, 4]

list_a.reverse()

print(list_a)

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Output

[4, 3, 2, 1]

Example 2:

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list_a = ["apple", "mango", "banana"]

list_a.reverse()

print(list_a)

 

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Output

['banana', 'mango', 'apple']