Collection of Python data types

40. Collection of Python data types

1. Python data types

There are 8 common data types in Python:

[data type data]

1. String: str, characters enclosed in quotation marks.
2. Integer: int, a number without a decimal point.
3. Floating point number: float, a number with a decimal point.
4. Boolean type: bool, only 2 values ​​( True and False ).

[Data of container type]

5. List: list, use English square brackets [ ] to store one of python8 data types, or any number of them.
6. Tuple: tuple, use English parentheses ( ) to store one of python8 data types, or any of several.
7. Dictionary: dict, use English braces { } to store multiple pairs of data with corresponding relationships.
8. Set: set, use English braces { } to store unordered, non-repeated, and immutable data.

2. What is a set

set[set]: set, a group, a set.

A collection is an iterable, unordered container type of data that cannot contain duplicate elements.

3. Characteristics of collections

  1. Sets are represented by curly braces { }.

  2. The elements of a collection are unordered.

  3. The elements of a collection cannot be repeated.

  4. The elements of a collection can only be of immutable data types.

  5. Collections themselves are mutable data types.

[Kind tips]

The elements of a collection are immutable.

Collections themselves are mutable: that is, collection elements can be added, removed, and emptied.

4. The Syntax of Collections

The collection mainly consists of 3 parts:

  1. English braces { }
  2. elements of a collection
  3. Elements are separated by commas

5. Create a new empty collection

5.1 Use English braces { } to create an empty dictionary instead of an empty collection

Using English square brackets [ ] we can create an empty list.

Using English parentheses ( ) we can create an empty tuple.

Using curly braces { } we can create an empty dictionary.

[Kind tips]

Both dictionaries and collections are represented by English braces { }, but English braces { } can only create empty dictionaries but not empty collections.

# create an empty list
none_list = [ ]

# Create a new empty tuple
none_tuple = ( )

# create an empty dictionary
none_dict ={ }

# type function view data type
print(type(none_list))
print(type(none_tuple))
print(type(none_dict))

[Terminal output]

<class 'list'>
<class 'tuple'>
<class 'dict'>

none[nʌn]: none, none, default value.

5.2 Create an empty collection with the set function

# create an empty collection
none_set = set( )

# type function view data type
print(type(none_set))

[Terminal output]

<class 'set'>

[code analysis]

  1. none_set is my name for the empty set.

  2. = is an assignment symbol.

  3. set is the function name.

  4. The function name set is followed by an English parenthesis ( ).

6. Create a collection

There are usually 2 ways to create a non-empty collection:

Method 1: Add elements directly in English braces { }.

Method 2: Use the set function to convert the iterable object into a collection.

6.1 Create a collection whose elements are strings

# A collection whose elements are strings
set_1 = {'a','a','a','a'}

print('A collection whose elements are strings',set_1)

[Terminal output]

A collection whose elements are strings {'a'}

[code analysis]

The element types of the above collections are all strings.

Strings are immutable data types.

Although 4 character strings 'a' are added in the curly brackets { } when creating the set, the elements of the set cannot be repeated, so only 1 character string 'a' is reserved in the output result.

6.2 Create a set whose elements are integers

# set of integers
set_2 = {1, 3, 9, 9, 9, 9}

print('set of integers',set_2)

[Terminal output]

set of integers {1, 3, 9}

[code analysis]

The element types of the above collections are all integers.

Integers are immutable data types.

Although 6 integers are added in the curly brackets { } when creating the set, the elements of the set cannot be repeated, so only 1 integer 9 is reserved in the output result.

6.3 Create a collection whose elements are floating-point numbers

# A collection whose elements are floating-point numbers
set_3 = {0.5, 1.1, 1.1 ,1.1} 

print('A collection whose elements are floating-point numbers',set_3)

[Terminal output]

A collection whose elements are floating-point numbers {0.5, 1.1}

[code analysis]

The element types of the above collections are all floating point numbers.

Floating point numbers are immutable data types.

Although 4 floating-point numbers are added in the curly brackets { } when creating a collection, the elements of the collection cannot be repeated, so only 1 floating-point number 1.1 is reserved in the output result.

6.4 Create a set whose elements are tuples

# A collection whose elements are tuples
# The tuple is represented by ()
set_4 = {('Life is too short',  'I use Python'),('Life is too short',  'I use Python'),('Life is too short',  'I use Python')}

print('A collection whose elements are tuples',set_4)

[Terminal output]

A collection whose elements are tuples {('Life is too short', 'I use Python')}

[code analysis]

The element types of the above collections are tuples.

Tuples are immutable data types.

Although 3 identical tuples are added in the curly brackets { } when creating a collection, the elements of the collection cannot be repeated, so only 1 tuple is retained in the output result.

6.5 Creating collections whose elements are Boolean values

# A collection whose elements are Boolean values
# Boolean: True, False
set_5 = {True, False, True, False}

print('A collection whose elements are Boolean values',set_5)

[Terminal output]

A collection whose elements are Boolean values {False, True}

[code analysis]

The element types of the above collections are all boolean values.

Boolean values ​​are immutable data types.

Although 4 Boolean values ​​are added in the curly brackets { } when creating a collection, the elements of the collection cannot be repeated, so only 2 Boolean values ​​are reserved in the output result.

6.6 The elements of a collection cannot be lists

# collection whose elements are lists
# The list is represented by []
set_6 = {['Zhang San','Li Si','Zhang San']}

print('collection whose elements are lists',set_6)

[Terminal output]

TypeError: unhashable type: 'list'

[code analysis]

The elements of the collection are lists, and the list is a variable data type, and the program reports an error.

unhashable type: 'list': Unhashable type: 'list'.

6.7 The elements of a collection cannot be dictionaries

# A collection whose elements are dictionaries
# Dictionaries are also represented by {}
dict_1 = {
    'name':'Andy',
    'age':'20',
    'sex':'female'
}

set_7 = {dict_1}
print('A collection whose elements are dictionaries',set_7)

[Terminal output]

TypeError: unhashable type: 'dict'

[code analysis]

The elements of the collection are dictionaries, dictionaries are variable data types, and the program reports an error.

unhashable type: 'dict': Unhashable type: 'dict'.

6.8 The elements of a collection cannot be collections

# A collection whose elements are collections
# Sets are represented by {}
set_8 = {{'a','b'}}

print('A collection whose elements are collections',set_8)

[Terminal output]

TypeError: unhashable type: 'set'

The elements of the collection are collections, which are variable data types, and the program reports an error.
unhashable type: 'set': Unhashable type: 'set'.

6.9. Creating Collections Containing Multiple Data Types

# The elements of the collection contain multiple data types
set_9 = {'a','b',True, 2, 9.9 , 9.9 }

print('The elements are collections of various data',set_9)

[Terminal output]

The elements are collections of various data {True, 2, 'b', 9.9, 'a'}

[Kind tips]

The collection is unordered: the order of the collection elements output after clicking Run may be different from the order of the elements we created the collection.

6.10 Convert an iterable to a collection with the set function

This knowledge point is written in a separate section.

7. The elements of a collection can only be immutable data types

Immutable data types:

  1. string

  2. integer

  3. floating point number

  4. tuple

  5. Boolean type

Mutable data types:

  1. the list

  2. dictionary

  3. gather

8. Summary

Tags: Python programming language

Posted by BRAINDEATH on Thu, 01 Dec 2022 10:21:13 +1030