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
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Sets are represented by curly braces { }.
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The elements of a collection are unordered.
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The elements of a collection cannot be repeated.
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The elements of a collection can only be of immutable data types.
-
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:
- English braces { }
- elements of a collection
- 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]
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none_set is my name for the empty set.
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= is an assignment symbol.
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set is the function name.
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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:
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string
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integer
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floating point number
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tuple
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Boolean type
Mutable data types:
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the list
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dictionary
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gather
8. Summary
