PYTHON-FUNDAMENTALS: CONSTANTS, VARIABLES AND DATA TYPES

hi,everyody
I am kavin. I am going to write which I learnt I my class.

Variables

A variable in Python is a symbolic name that references or points to an object. Once a variable is assigned a value, it can be used to refer to that value throughout the program. Variables act as containers for storing data values.

How to name a variables

1.Start with a letter or an underscore.
2.Followed by letters, digits, or underscores.
3.Case-sensitive
4.Don’t use Python Keywords

Examples of Valid Variable Names:
my_variable
variable1
_hidden_variable
userName


Assigning Values to Variables

In Python, the assignment operator = is used to assign values to variables. The syntax is straightforward: variable_name = value.
eg:

<span>>>></span><span>name</span><span>=</span><span>"</span><span>kavin</span><span>"</span>
<span>>>></span><span>print</span><span>(</span><span>name</span><span>)</span>
<span>>>></span><span>kavin</span>
<span>>>></span><span>name</span><span>=</span><span>"</span><span>kavin</span><span>"</span>
<span>>>></span><span>print</span><span>(</span><span>name</span><span>)</span>

<span>>>></span><span>kavin</span>
>>>name="kavin"
>>>print(name)

>>>kavin

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Multiple Assignments

Python allows you to assign values to multiple variables in a single line. This can make your code more concise and readable.
eg:

<span>>>></span><span>a</span><span>,</span><span>b</span><span>,</span><span>c</span><span>=</span><span>1</span><span>,</span><span>2</span><span>,</span><span>3</span>
<span>>>></span><span>print</span><span>(</span><span>a</span><span>,</span><span>b</span><span>,</span><span>c</span><span>)</span>
<span>>>></span><span>a</span><span>,</span><span>b</span><span>,</span><span>c</span><span>=</span><span>1</span><span>,</span><span>2</span><span>,</span><span>3</span>
<span>>>></span><span>print</span><span>(</span><span>a</span><span>,</span><span>b</span><span>,</span><span>c</span><span>)</span>
>>>a,b,c=1,2,3
>>>print(a,b,c)

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Variable Types

Python is a dynamically typed language, which means you don’t need to declare the type of a variable when assigning a value to it. The type is inferred at runtime based on the assigned value.
eg:

<span>>>></span><span>my_variable</span><span>=</span><span>"</span><span>10</span><span>"</span>
<span>>>></span><span>my_variable</span> <span>is</span> <span>an</span> <span>integer</span>
<span>>>></span><span>my_variable</span><span>=</span><span>"</span><span>10</span><span>"</span>

<span>>>></span><span>my_variable</span> <span>is</span> <span>an</span> <span>integer</span>
>>>my_variable="10"

>>>my_variable is an integer

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You can check the type of a variable using the type() function.
eg:

<span>>>></span><span>type</span><span>(</span><span>"</span><span>hello</span><span>"</span><span>)</span>
<span>>>><</span><span>class</span><span>'</span><span>str</span><span>'</span><span>></span>
<span>>>></span><span>type</span><span>(</span><span>"</span><span>hello</span><span>"</span><span>)</span>

<span>>>><</span><span>class</span><span>'</span><span>str</span><span>'</span><span>></span>
>>>type("hello")

>>><class'str'>

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Constants

In Python, constants are variables whose values are not meant to change. By convention, constants are typically written in all uppercase letters with underscores separating words.
eg:

<span>>>></span><span>PI</span><span>=</span><span>22</span><span>/</span><span>7</span>
<span>>>></span><span>PI</span><span>=</span><span>22</span><span>/</span><span>7</span>
>>>PI=22/7

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Data Types

Data types are the different kinds of values that you can store and work with.

1.Numeric Types
*Integer (int): Whole numbers.

>>>value=23
>>>value=23
>>>value=23

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*Float (float): Decimal numbers.

>>>value=23.5
>>>value=23.5
>>>value=23.5

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*Complex (complex): Complex numbers.

>>>value=2+3j
>>>value=2+3j
>>>value=2+3j

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2. Text Type

String (str): Sequence of characters.
eg:

<span>>>></span><span>message</span><span>=</span><span>"</span><span>hello mac</span><span>"</span>
<span>>>></span><span>message</span><span>=</span><span>"</span><span>hello mac</span><span>"</span>
>>>message="hello mac"

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3. Boolean Type

Boolean (bool): Represents True or False.
eg:

<span>>>></span><span>my_project</span><span>=</span><span>True</span>
<span>>>></span><span>my_project</span><span>=</span><span>True</span>
>>>my_project=True

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4. None Type

NoneType: Represents the absence of a value
eg:

>>>result=none
>>>result=none
>>>result=none

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5. Sequence Types

*List (list): Ordered, mutable collection
eg:

<span>>>></span><span>fruits</span><span>=</span><span>[</span><span>apple</span><span>,</span><span>cherry</span><span>,</span><span>mango</span><span>]</span>
<span>>>></span><span>fruits</span><span>=</span><span>[</span><span>apple</span><span>,</span><span>cherry</span><span>,</span><span>mango</span><span>]</span>
>>>fruits=[apple,cherry,mango]

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*Tuple (tuple): Ordered, immutable collection.
eg:

<span>>>></span><span>coordinates</span><span>(</span><span>3</span><span>,</span><span>4</span><span>)</span>
<span>>>></span><span>coordinates</span><span>(</span><span>3</span><span>,</span><span>4</span><span>)</span>
>>>coordinates(3,4)

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*Range (range): Sequence of numbers.
eg:

<span>>>></span><span>number</span><span>=</span><span>range</span><span>(</span><span>1</span><span>,</span><span>10</span><span>)</span>
<span>>>></span><span>number</span><span>=</span><span>range</span><span>(</span><span>1</span><span>,</span><span>10</span><span>)</span>
>>>number=range(1,10)

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6. Mapping Type

Dictionary (dict): Unordered, mutable collection of key-value pairs.
eg:

<span>>>></span><span>person</span><span>=</span><span>{</span><span>"</span><span>name</span><span>"</span><span>:</span><span>"</span><span>kavin</span><span>"</span><span>,</span><span>"</span><span>url</span><span>"</span><span>:</span><span>"</span><span>https://www.kavin.com</span><span>"</span><span>}</span>
<span>>>></span><span>person</span><span>=</span><span>{</span><span>"</span><span>name</span><span>"</span><span>:</span><span>"</span><span>kavin</span><span>"</span><span>,</span><span>"</span><span>url</span><span>"</span><span>:</span><span>"</span><span>https://www.kavin.com</span><span>"</span><span>}</span>
>>>person={"name":"kavin","url":"https://www.kavin.com"}

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7.Set Type

Set (set): Unordered collection of unique elements.
Eg:

<span>>>></span><span>unique_number</span><span>=</span><span>{</span><span>2</span><span>,</span><span>3</span><span>,</span><span>4</span><span>}</span>
<span>>>></span><span>unique_number</span><span>=</span><span>{</span><span>2</span><span>,</span><span>3</span><span>,</span><span>4</span><span>}</span>
>>>unique_number={2,3,4}

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Frozenset (frozenset): Immutable set.
eg:

<span>>>></span><span>frozen_set</span><span>=</span><span>frozena</span><span>([</span><span>2</span><span>,</span><span>3</span><span>,</span><span>4</span><span>])</span>
<span>>>></span><span>frozen_set</span><span>=</span><span>frozena</span><span>([</span><span>2</span><span>,</span><span>3</span><span>,</span><span>4</span><span>])</span>
>>>frozen_set=frozena([2,3,4])

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Checking Data Type

Syntax: type(variable_name)
eg:

<span>>>></span><span>name</span><span>=</span><span>"</span><span>kavin</span><span>"</span>
<span>>>></span><span>print</span><span>(</span><span>type</span><span>(</span><span>name</span><span>))</span>
<span>>>></span> <span><</span><span>class</span><span>'</span><span>int</span><span>'</span><span>></span>
<span>>>></span><span>name</span><span>=</span><span>"</span><span>kavin</span><span>"</span>
<span>>>></span><span>print</span><span>(</span><span>type</span><span>(</span><span>name</span><span>))</span>

<span>>>></span> <span><</span><span>class</span><span>'</span><span>int</span><span>'</span><span>></span>
>>>name="kavin"
>>>print(type(name))

>>> <class'int'>

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this is the things which i learnt in the class of Variables, Constants and Data Types.
Thank You

原文链接：PYTHON-FUNDAMENTALS: CONSTANTS, VARIABLES AND DATA TYPES